Description:HAPTIC DEVICE FOR 6DOF PARALLEL MANIPULATION

FIELD OF THE PRESENT DISCLOSURE
[0001] The present disclosure relates to a haptic device. More particularly, the disclosure pertains to a haptic device comprising a 6-6 Stewart platform operating as a 6DoF (degree-of-freedom) parallel manipulator which offers higher precision, stability, and responsiveness over conventional haptic devices. Further, the present disclosure provides a system incorporating such haptic device and a method for implementing the said system.

BACKGROUND
[0002] Haptic devices, also referred to as 3D touch devices, utilize technology that can create an experience of touch by applying forces, vibrations, or motions to the user, and also receive such forces and motions from the user. Earlier where human-computer interactions were limited to mere visual or auditory feedback; with haptic devices, users can now feel what they see or control, providing a more immersive and interactive experience. Particularly in robotics and computer interfaces, the haptic devices play a major role for replicating and augmenting human sense of touch. However, haptic devices have some challenges, with primary concern being precision. The human sense of touch is very sensitive, capable of detecting minute differences in pressure. Replicating or creating a sensation that feels authentic requires precise calibration and fine-tuning. Size and scalability pose another challenge. While it might be feasible to have a large haptic setup in a controlled environment (like a research lab), commercial and home applications require devices that are compact without compromising on their efficiency and effectiveness.
[0003] Traditional haptic devices often relied on basic vibration mechanisms to convey feedback. More advanced systems, especially in specialized fields like telesurgery, utilized complex mechanical setups. These often included gloves or armatures equipped with an array of motors and sensors. Such systems could provide more detailed feedback, such as the resistance felt during a surgical procedure, but are often bulky, expensive, and require extensive training. Even with advanced mechanisms, replicating the intricacies of touch with absolute precision remains a challenge. Moreover, high-precision haptic systems, given their complexity, are often expensive, limiting their accessibility to niche applications.
[0004] Stewart Platform, specifically 6-6 Stewart Platform, has been extensively used in robotics. This mechanism, known for its six degrees of freedom (DoF), i.e., translational movements along X, Y, and Z axes and rotational movements around these axes, found its application extensively in flight simulators, precision machinery, and, more importantly, haptic devices. Haptic devices utilizing the 6-Stewart platform consist of a top plate and a bottom plate, connected by six extensible legs. Such structure enables these devices to render real-world tactile sensations in a digital or remote-controlled environment. However, conventional 6-Stewart platform designs often have limited workspaces due to the geometrical and mechanical constraints inherent in their design. This limitation restricts the range of motion and is particularly problematic for applications that require extensive freedom of movement. Further, such conventional platforms might offer a limited range of haptic sensations, potentially reducing the range of applications they can be used for.
[0005] In light of the limitations of conventional haptic systems utilizing the 6-Stewart platform, the present disclosure aims to provide a haptic device that offers high precision, stability, and responsiveness, leveraging a 6-6 Stewart platform configuration.

SUMMARY
[0006] In an aspect, a haptic device is disclosed. Herein, the haptic device is adapted to be operated as a 6DoF (degree-of-freedom) parallel manipulator. The haptic device comprises a base platform and a mobile platform. The haptic device further comprises a set of rotary actuators arranged at the base platform and provided with a revolute joint. The haptic device further comprises a plurality of legs flexibly connecting the mobile platform to the base platform, with each one of the plurality of legs comprising a crank coupled to the revolute joint of one of the set of rotary actuators and a first spherical joint, and a link coupled to the first spherical joint and a second spherical joint positioned at the mobile platform. Two proximate legs of the plurality of legs at the base platform diverge at the mobile platform.
[0007] In one or more embodiments, each one of the sets of rotary actuators comprises at least one motor, such that the motors placed within the base platform are organized in pairs, with axes of adjacent motors in each of the pairs being coincident.
[0008] In one or more embodiments, the set of rotary actuators comprises at least six rotary actuators, and wherein the motors are organized in three groups, and wherein the axes of the three groups are oriented 120 degrees apart from each other.
[0009] In one or more embodiments, the motor is a brushless direct-current (BLDC) motor configured to generate high torque at low rotations per minute (RPM).
[0010] In one or more embodiments, each one of the set of rotary actuators is attached to a spring for gravity balancing of the base platform.
[0011] In one or more embodiments, the base platform forms a hexagon inscribed in a circle with a diameter in a range of 230 mm to 250 mm and the mobile platform forms a hexagon inscribed in a circle with a diameter in a range of 110 mm to 140 mm.
[0012] In one or more embodiments, the link in each one of the plurality of legs has a length in a range of 160 mm to 200 mm and the crank in each one of the plurality of legs has a length in a range of 40 mm to 60 mm.
[0013] In one or more embodiments, each of the first spherical joints and each of the second spherical joints is a ball and socket type joint having a cone angle limited to a range of 48 degrees to 62 degrees.
[0014] In one or more embodiments, the haptic device further comprises a stopper associated with the revolute joint of each one of the set of rotary actuators to restrict motion range thereof.
[0015] In one or more embodiments, the haptic device further comprises a manipulandum positioned on the mobile platform, wherein the manipulandum comprises a user interface mechanism configured to capture user interactions, and generate control signals to govern the set of rotary actuators based on the user interactions.
[0016] In one or more embodiments, the haptic device further comprises an encoder associated with each one of the set of rotary actuators, and wherein the encoder is configured to detect a rotational position of the corresponding one of the set of rotary actuators.
[0017] In one or more embodiments, the haptic device further comprises a first Inertial Measurement Unit (IMU) located on the base platform and a second IMU located on the mobile platform, and wherein the first and second IMUs are configured to measure angular readings corresponding to relative positioning of the mobile platform with respect to the base platform resulting from user interactions.
[0018] In one or more embodiments, the mobile platform further comprises a damping arrangement based on a Stewart structure, and wherein the damping arrangement comprises a first plate and a second plate interconnected by a set of flexure units, and each one of the set of flexure units comprising a linear leaf-spring based flexure sandwiched between two notch joints, allowing a longitudinal rotational twist about axis of corresponding one of the set of flexure units, to reject high-frequency, low-amplitude disturbances.
[0019] In another aspect, a system is disclosed. The system comprises a haptic device. The haptic device comprises a base platform and a mobile platform. The haptic device further comprises a set of rotary actuators arranged at the base platform and provided with a revolute joint. The haptic device further comprises a plurality of legs flexibly connecting the mobile platform to the base platform, with each one of the plurality of legs comprising a crank coupled to the revolute joint of one of the set of rotary actuators and a first spherical joint, and a link coupled to the first spherical joint and a second spherical joint positioned at the mobile platform. Two proximate legs of the plurality of legs at the base platform diverge at the mobile platform. The system further comprises a controller configured to translate the user interactions as control instructions for a robotic device. Herein, the robotic device comprises a set of end-effectors adapted to replicate user movements based on the control instructions, and transmit haptic feedback signals corresponding to encountered resistances by the set of end-effectors to the controller. Further, herein, the controller is configured to govern the set of rotary actuators based on the haptic feedback signals, enabling a bi-directional communication between the user and the robotic device.
[0020] In yet another aspect, a method is disclosed. The method comprises providing a haptic device comprising: a base platform; a mobile platform; a set of rotary actuators arranged at the base platform, each actuator having a revolute joint; a plurality of legs connecting the mobile platform to the base platform, wherein each leg comprises a crank connected to the revolute joint of an associated rotary actuator and a first spherical joint, and a link coupled between the first spherical joint and a second spherical joint located at the mobile platform; and a manipulandum on the mobile platform, configured to capture user interactions. The method further comprises capturing, via the manipulandum, user interactions with the haptic device. The method further comprises translating the captured user interactions into control instructions for a robotic device. The method further comprises receiving haptic feedback signals corresponding to encountered resistances by a set of end-effectors of the robotic device while replicating user movements based on the control instructions. The method further comprises governing the set of rotary actuators based on the haptic feedback signals, enabling a bi-directional communication between the user and the robotic device.
[0021] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE FIGURES
[0022] For a more complete understanding of example embodiments of the present disclosure, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:
[0023] FIG. 1A illustrates a diagrammatic view representation of a haptic device, in accordance with one or more embodiments of the present disclosure;
[0024] FIG. 1B illustrates another diagrammatic view representation of the haptic device, in accordance with one or more embodiments of the present disclosure;
[0025] FIG. 1C illustrates yet another diagrammatic view representation of the haptic device, in accordance with one or more embodiments of the present disclosure;
[0026] FIG. 1D illustrates a diagrammatic view representation of the haptic device with a cover removed to show inner components thereof, in accordance with one or more embodiments of the present disclosure;
[0027] FIG. 1E illustrates a section view representation of the haptic device depicting the inner components thereof, in accordance with one or more embodiments of the present disclosure;
[0028] FIG. 1F illustrates a detailed diagrammatic view representation of a revolute joint of the haptic device, in accordance with one or more embodiments of the present disclosure;
[0029] FIG. 1G illustrates a detailed diagrammatic view representation of a manipulandum of the haptic device, in accordance with one or more embodiments of the present disclosure;
[0030] FIG. 1H illustrates a diagrammatic view representation of a damping arrangement incorporated in a mobile platform of the haptic device, in accordance with one or more embodiments of the present disclosure;
[0031] FIG. 1I illustrates another diagrammatic view representation of the damping arrangement, in accordance with one or more embodiments of the present disclosure;
[0032] FIG. 1J illustrates a diagrammatic view representation of a flexure unit of the damping arrangement, in accordance with one or more embodiments of the present disclosure;
[0033] FIG. 1K illustrates a section view representation of the flexure unit, in accordance with one or more embodiments of the present disclosure;
[0034] FIG. 2 illustrates a block diagram representation of a system incorporating the haptic device to control a robotic device, in accordance with one or more embodiments of the present disclosure;
[0035] FIG. 3 illustrates a circuit diagram of the system incorporating the haptic device, in accordance with one or more embodiments of the present disclosure;
[0036] FIG. 4 illustrates a flow diagram representation of a method of implementation of the haptic device, in accordance with one or more embodiments of the present disclosure; and
[0037] FIG. 5 illustrates a depiction of an exemplary implementation of the haptic device, in accordance with one or more embodiments of the present disclosure.

DETAILED DESCRIPTION
[0038] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure is not limited to these specific details.
[0039] Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. The appearance of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not for other embodiments.
[0040] Furthermore, in the following detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present disclosure.
[0041] Embodiments described herein may be discussed in the general context of computer-executable instructions residing on some form of computer-readable storage medium, such as program modules, executed by one or more computers or other devices. By way of example, and not limitation, computer-readable storage media may comprise non-transitory computer-readable storage media and communication media; non-transitory computer-readable media include all computer-readable media except for a transitory, propagating signal. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or distributed as desired in various embodiments.
[0042] Some portions of the detailed description that follows are presented and discussed in terms of a process or method. Although steps and sequencing thereof are disclosed in figures herein describing the operations of such process or method, such steps and sequencing are exemplary. Embodiments are well suited to performing various other steps or variations of the steps recited in the flowchart of the figure herein, and in a sequence other than that depicted and described herein.
[0043] Some portions of the detailed descriptions that follow are presented in terms of procedures, logic blocks, processing, and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. In the present application, a procedure, logic block, process, or the like, is conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those utilizing physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as transactions, bits, values, elements, symbols, characters, samples, pixels, or the like.
[0044] Referring now to FIGS. 1A-1E, in combination, illustrated are diagrammatic representations of a haptic device (as represented by reference numeral 100), in accordance with one or more embodiments of the present disclosure. The haptic device 100 represents a development in tactile feedback systems, integrating accurate engineering with practical design. Each component of the haptic device 100 is optimized for performance and contributes to the overall efficiency. The design strategy of the haptic device 100 ensures its responsiveness and accuracy to user inputs, providing an immediate feedback loop. The primary function of the haptic device 100 is to accurately mimic tactile sensations. This capability allows users to interact with digital interfaces or entities in a realistic manner. The design of the haptic device 100 of the present disclosure supports various applications without requiring significant modifications. The versatility of the haptic device 100 is evident in its wide range of applications, from virtual reality to teleoperation.
[0045] The haptic device 100 embodies a design configuration adapted to be operated as a 6DoF (degree-of-freedom) parallel manipulator. The haptic device 100 includes a base platform 102, a mobile platform 104, a set of rotary actuators 106, and a plurality of legs 108. Herein, the base platform 102 acts as a foundation of the haptic device 100, which remains stationary and serves as the anchoring point for the entire assembly. The mobile platform 104 is located directly above the base platform 102. The base platform 102 is constructed to offer a balance between rigidity and weight, ensuring consistent performance and stability during operation of the haptic device 100. The mobile platform 104 serves as the primary interface for user interaction. The mobile platform 104 is designed to move and adjust in multiple directions, capturing user interactions and translating them into corresponding haptic feedback. The mobile platform 104 is constructed to ensure fluid movement, minimizing friction and resistance, thus offering an intuitive user experience. The base platform 102 has the rotary actuators 106 integrated therewith. Further, the plurality of legs 108 flexibly connects the mobile platform 104 to the base platform 102.
[0046] The haptic device 100 converts intricate user movements into precise remote commands, allowing for intuitive interaction with remote or virtual environments. In the present disclosure, the integration and organization of rotary actuators 106 allow for the motion and feedback capabilities of the haptic device 100. The specific configuration of the present haptic device 100 overcomes limitations encountered in conventional haptic devices, primarily those related to issues of singularity and constraint. In conventional setups, singularity refers to configurations where the mechanism loses its ability to move in specific directions, thereby leading to a loss of control and precision. This is typically a concern in parallel manipulators like the 6-Stewart platform where specific alignments can lead to locked or undefined states, affecting the real-time responsiveness and accuracy of the device. The present haptic device 100 bypasses such singularities, maintaining consistent control and feedback across all degrees of freedom, ensuring that the user interactions are seamlessly translated without the risk of encountering locked states or loss of movement in any direction.
[0047] In particular, herein, each of the rotary actuators 106 is accompanied by a revolute joint (as represented by reference numeral 110), allowing for precise rotational movement. FIG. 1F illustrates a portion of the haptic device 100 detailing the rotary actuator 106 thereof. As better seen in FIG. 1E and FIG. 1F, the revolute joint 110 is implemented in the form of a cap placed over each of the rotary actuators 106. Further, each leg in the plurality of legs 108 integrates a crank 112, directly linked to the revolute joint 110 of one of the rotary actuators 106, and a first spherical joint 114. Furthermore, a link 116 connects the first spherical joint 114 to a second spherical joint 118 located on the mobile platform 104. The haptic device 100 incorporates the first spherical joints 114 and the second spherical joints 118 to facilitate the dynamic movements of the mobile platform 104. These spherical joints 114, 118 together with the revolute joint 110 makes the haptic device 100 to function as an RSS (Revolute-Spherical-Spherical) spatial serial manipulator. Notably, two adjacent legs of the plurality of legs 108 starting from the base platform 102 have a diverging configuration when they connect to the mobile platform 104. That is, as seen from FIGS. 1A-1C, two adjacent legs of the plurality of legs 108 that are proximate to each other at the base platform 102 diverge as they extend and connect to the mobile platform 104. This unique diverging design ensures a broader range of motion and enhanced stability for the mobile platform. The collective integration of these components, i.e., the base platform 102, the mobile platform 104, the rotary actuators 106, and the plurality of legs 108, constitutes a Stewart platform, functioning as a parallel manipulator.
[0048] More specifically, the set of rotary actuators 106 includes at least six individual rotary actuators. In the present embodiments, the haptic device 100 is shown to have six rotary actuators 106 for all implementations. Each of these actuators 106 is designed to convert electrical energy into rotational motion, allowing the haptic device 100 to achieve the desired movements and provide the necessary tactile feedback. The inclusion of six rotary actuators 106 ensures that the haptic device 100 can achieve a comprehensive range of motion across multiple axes. By distributing the motion responsibilities across these six actuators 106, the haptic device 100 can ensure more precise and controlled movements, especially when complex or simultaneous motions are required. Furthermore, the strategic design and placement of these six rotary actuators 106 on the base platform 102 ensures an even distribution of forces and allows for coordinated actions between them, as required for maintaining the stability of the mobile platform 104, especially during dynamic interactions. With such arrangement, the haptic device 100 constitutes a 6-6 Stewart platform, functioning as a 6DoF (degree of freedom) parallel manipulator.
[0049] In the present implementations, within the haptic device 100, each of the set of rotary actuators 106 incorporates a motor 120. These motors 120 serve as the primary drivers, converting electrical signals into the mechanical rotational motion for providing tactile feedback to the user, in the haptic device 100. Also, the arrangement of these motors 120 on the base platform 102 follows a systematic paired configuration. Specifically, the motors 120 are organized into pairs, resulting in adjacent motors within each pair sharing a coincident axis. This coincident axis configuration implies that the rotational axes of the two motors 120 in each pair align with one another. Such a paired and coincident axis arrangement ensures a compact and efficient design, maximizing the use of space on the base platform 102. Further, this configuration aligns the axes of adjacent motors 120 so that the haptic device 100 can achieve synchronized and harmonized movements for precise and smooth haptic feedback. This alignment also minimizes any potential mechanical interferences or conflicts that could arise from asynchronous motor operations.
[0050] As discussed, the haptic device 100 incorporates at least six rotary actuators 106 with the motors 120 being organized into pairs, consequently the six motors 120 associated with the set of rotary actuators 106 are organized into three distinct groups. This means that the motors 120 in the haptic device 100 is divided into pairs of two, with each pair functioning in tandem for specific operations. Herein, the axes of each of these three groups are oriented at an angle of 120 degrees relative to each other. Such a 120-degree separation between the axes of the motor groups ensures a uniform distribution of the motors 120 around the base platform 102. This equidistant angular separation facilitates a wider range of motion, allowing the haptic device 100 to achieve comprehensive three-dimensional movements without mechanical obstructions. Further, the 120-degree orientation ensures balanced force distribution across the base platform 102, for maintaining the stability and precision of the haptic device 100 during operation. This configuration also aids in minimizing potential mechanical interferences between the motor pairs, ensuring synchronized and harmonized movements essential for accurate haptic feedback.
[0051] In the present configuration, the specified motor 120 used in each of the rotary actuators 106 is a brushless direct-current (BLDC) motor. The BLDC motor 120 is distinct from traditional brushed motors due to the absence of brushes, leading to reduced wear and tear, longer lifespan, and increased efficiency. The use of the BLDC motor 120 in the haptic device 100 is due to its ability to generate high torque even at low rotations per minute (RPM). This capability is important for operations of the haptic device 100, especially in applications that require precise and controlled movements. The high torque ensures that the haptic device 100 can exert significant force or resistance with minimal rotational speed, allowing for smoother and more responsive tactile feedback. That is, it ensures that the haptic device 100 can provide strong and consistent haptic feedback even under conditions that demand slow and deliberate movements. Further, the use of BLDC motor 120 enhances efficiency of the haptic device 100 since high torque at low RPMs often translates to lower energy consumption, leading to prolonged operational times and reduced power requirements. In the present implementations, the BLDC motor 120 is configured to produce approximately 0.6 N-m of nominal torque at about 240 rpm.
[0052] In the present configuration, the rotary actuators 106 are direct-driven BLDC motors 120 with multiple poles. Multiple poles in the motor design contribute to smoother torque production and increased efficiency. Additionally, the winding of these motors is executed in a specialized manner. This specific winding technique is designed to generate high torque values even at low rotations per minute (RPM). The specialized winding and high inductance offer advantages in terms of torque production. Herein, considerations are made to ensure that the resultant back EMF does not adversely impact performance of the haptic device 100.
[0053] In an embodiment, each one of the set of rotary actuators 106 is attached to a spring 122 (as visible in FIG. 1E) for gravity balancing of the base platform 102. As used herein, gravity balancing refers to the mechanism where the gravitational forces acting on the haptic device 100 are counteracted, ensuring that the base platform 102 remains stable and maintains its orientation irrespective of the movements of the mobile platform 104 or any external interactions. Specifically, when the mobile platform 104 moves (for example, due to user interactions), gravitational forces tend to shift the equilibrium of the base platform 102. However, with the springs 122 attached to each of the rotary actuators 106, these gravitational forces are counterbalanced. The springs 122, based on their elasticity and tension, exert an opposing force that nullifies the effect of gravity, thus stabilizing the base platform 102.
[0054] In an embodiment, the base platform 102 forms a hexagon inscribed in a circle with a diameter in a range of 230 mm to 250 mm (specifically, in an example configuration, 243 mm) and the mobile platform 104 forms a hexagon inscribed in a circle with a diameter in a range of 110 mm to 140 mm (specifically, in an example configuration, 150 mm). This choice of a hexagon is driven by engineering considerations, especially with its inherent properties allowing to accommodate the motor groups placed at required orientation in the present configuration of the haptic device 100. For the base platform 102, a hexagon, with its six equal sides and angles, provides uniformity in structural design to provide an even distribution of mechanical stresses and forces, enhancing its stability during operations. This hexagonal base platform 102 is further characterized by being inscribed within a circle having a specific diameter, approximately 243 mm. This particular diameter has been chosen to strike a balance between providing a substantial operational workspace for the rotary actuators and other components while ensuring the haptic device 100 remains compact and efficient in terms of space utilization. For the mobile platform 104, the hexagonal shape ensures that any force or interaction applied thereto is uniformly distributed, enhancing its adaptability to various movements and interactions. The mobile platform 104 has its hexagon shape inscribed within a circle of a smaller diameter, approximately 130 mm. This reduced size, compared to the base platform 102 facilitates rapid and precise movements, and thus better responsiveness to user inputs by the mobile platform 104.
[0055] Further, in an embodiment, the link 116 in each one of the plurality of legs 108 has a length in a range of 160 mm to 200 mm (specifically, in an example configuration, 183 mm) and the crank 112 in each one of the plurality of legs 108 has a length in a range of 40 mm to 60 mm (specifically, in an example configuration, 53 mm). These components, with their specified lengths, play vital roles in ensuring the effective operation of and accurate tactile feedback in the haptic device 100. As discussed, the link 116 serves as a connecting element between the first and second spherical joints 114, 118 for the transmission of motions and forces therebetween, and thus allowing the mobile platform to achieve its desired range of movements. The specified length of the link 116 is chosen to provide optimal distance between the two spherical joints 114, 118, ensuring that the haptic device 100 can achieve a broad range of motion without mechanical restrictions. Furthermore, this specific length of the link 116 ensures stability and prevents overextension of the corresponding leg 108, which could compromise accuracy of operations of the haptic device 100. Similarly, the specified length of the crank 112 ensures that the rotary motion from the rotary actuators 106 is translated effectively, allowing for precise and controlled movements of the mobile platform 104. Moreover, this specific length ensures that the crank 112 does not interfere with other components, allowing for smooth operation and reducing potential mechanical conflicts.
[0056] Also, in an embodiment, each of the first spherical joints 114 and each of the second spherical joints 118 is a ball and socket type joint having a cone angle limited to a range of 48 degrees to 62 degrees (specifically, in an example configuration, 52 degrees). As discussed, the spherical joints 114, 118 allow for multi-directional rotational movement, ensuring that the mobile platform 104 can achieve precise and varied movements in response to user interactions or feedback requirements, and thus granting the haptic device 100 a comprehensive range of motion. While the spherical joints 114, 118 offer significant flexibility, there is a restriction placed on their range of motion. Specifically, the cone angle, which denotes the maximum angle of rotation or tilt the spherical joints 114, 118 can achieve from its central position, is limited to approximately 52 degrees. Such a restriction ensures that the spherical joints 114, 118 do not overextend or rotate beyond mechanical limits, and the haptic device 100 can maintain precise control over its movements, ensuring accurate tactile feedback.
[0057] It may be appreciated that the above given dimensions and values are exemplary only and shall not be construed as limited to the present disclosure in any manner. It may also be understood that the given dimensions and values are for a given exemplary configuration (variation) of the haptic device 100; and in other configurations (variations) of the haptic device 100 (like scaled-up or scaled down versions), these dimensions and/or values may proportionately be increased or decreased as per requirements.
[0058] In some embodiments, the haptic device 100 includes a stopper 124 associated with the revolute joint 110 of each one of the set of rotary actuators 106 to restrict motion range thereof. As may be understood, the revolute joints 110, by its very nature, allow for rotational motion around a single axis. However, without any constraints, the revolute joints 110 could potentially rotate beyond desired mechanical limits, leading to mechanical strain, wear, or even damage to the haptic device. The primary purpose of the stopper 124 is to regulate and restrict the range of motion of the revolute joint 110, ensuring controlled and safe operation of the haptic device 100. The stopper 124 is strategically positioned to come into contact with a part of the revolute joint 110 once it reaches its predefined motion limit. When the revolute joint 110 rotates to this limit, the stopper 124 acts as a physical barrier, preventing any further rotation. Additionally, the stopper 124 provides an added safety mechanism where there might be forceful user interactions. As may be seen, in the present configurations, the stopper 124 is implemented in the form of a barrier for the revolute joint 110. However, it may be appreciated that the stopper 124 may be implemented in other suitable forms without departing from the spirit and the scope of the present disclosure.
[0059] Further, as illustrated, the haptic device 100 includes a manipulandum 126 positioned on the mobile platform 104. FIG. 1G illustrates a diagrammatic view of the manipulandum 126, in accordance with one or more embodiments of the present disclosure. The manipulandum 126 includes a user interface mechanism (not shown) configured to capture user interactions, and generate control signals to govern the set of rotary actuators 106 based on the user interactions. The manipulandum 126 serves as a primary point of interaction between the user and the present haptic device 100, functioning both as an input and feedback mechanism. The manipulandum 126 is configured to capture and interpret user interactions, such as pushes, pulls, twists, or any other form of tactile engagement. Depending on its design, the manipulandum 126 could be shaped or textured in a specific way to facilitate intuitive interactions, or it might incorporate additional features like buttons or touch-sensitive surfaces. Once the manipulandum 126 captures these user interactions, it processes them to generate corresponding control signals. These control signals are in the form of instructions that control how the set of rotary actuators 106 within the haptic device 100 should respond. For instance, if a user pushes the manipulandum 126 in a particular direction, the generated control signal might command specific rotary actuator(s) 106 to move, translating that push into a corresponding movement of the mobile platform 104.
[0060] The real-time conversion of user interactions into control signals ensures that the haptic device 100 can provide immediate feedback. For example, in a virtual reality application, if the user, via the manipulandum 126, interacts with a virtual object, the haptic device 100 can immediately provide tactile feedback corresponding to that interaction, such as resistance or vibration. Moreover, the capability of the manipulandum 126 to generate control signals based on user interactions ensures that the haptic device 100 can operate in a wide range of applications. Whether it's simulating the feel of a surgical instrument in a medical training simulation or providing feedback in a virtual gaming environment, the manipulandum 126 enables the haptic device 100 to cater to diverse tactile feedback requirements.
[0061] Furthermore, the haptic device 100 includes an encoder (not shown) associated with each one of the set of rotary actuators 106. Herein, the encoder is configured to detect a rotational position of the corresponding one of the set of rotary actuators 106. Such functioning of the encoder to detect and measure the rotational position of the rotary actuator 106 to which it is associated may be contemplated. As the rotary actuator 106 moves, be it due to user interactions or system commands, the encoder continuously tracks this motion. By doing so, the encoder provides real-time data on the angular position, speed, and direction of rotation of the rotary actuator 106. Such feedback from the encoder allows for dynamic adjustments. If any discrepancies arise between the desired and actual positions of the rotary actuator 106, the encoder data can be used to make immediate corrections, ensuring that the haptic device 100 remains responsive and accurate in its feedback.
[0062] Furthermore, the haptic device 100 also includes a first Inertial Measurement Unit (IMU) (not shown) located on the base platform 102 and a second IMU (not shown) located on the mobile platform 104. Herein, the first and second IMUs are configured to measure angular readings corresponding to relative positioning of the mobile platform 104 with respect to the base platform 102 resulting from user interactions. In the haptic device 100, the inclusion of IMUs further enhances its capability to provide precise and responsive tactile feedback. An IMU is an electronic device that measures and reports specific physical parameters, particularly angular velocity and linear acceleration, using a combination of accelerometers and gyroscopes, and sometimes magnetometers. In the context of the haptic device 100, the primary role of these IMUs is to capture angular readings. The first IMU, located on the base platform 102, provides a stable reference point. On the other hand, the second IMU on the mobile platform 104 continuously monitors its movements and changes in orientation resulting from user interactions or system commands. By comparing the data from both IMUs, the haptic device 100 can accurately determine the relative positioning and orientation of the mobile platform 104 with respect to the base platform 102. This ability to measure relative positioning is crucial for the operation of the haptic device 100. For instance, if a user tilts the manipulandum 126, the mobile platform 104 will correspondingly move. The second IMU captures this movement, and by comparing it with the reference data from the first IMU, the haptic device 100 can determine the exact nature and magnitude of the movement. This information can then be used to provide accurate tactile feedback or to generate control signals for other connected systems or simulations.
[0063] Also, as illustrated, the base platform 102 incorporates a user-centric design element in the form of strategically placed ON/OFF buttons 128. These buttons 128 are specifically designated for controlling the operational state of the rotary actuators 106 in the haptic device 100. Their primary function is to provide users with a direct and tactile means to switch the motors 120 on or off.
[0064] It may be noted that the haptic device 100 may suffer from high-frequency, low-amplitude disturbances, which can arise from various sources, such as minor vibrations in the environment, user inputs, or even inherent in the system's operation. These disturbances, while often minute, can adversely affect performance of the haptic device 100 and the quality of tactile feedback.
[0065] As better illustrated in FIG. 1E, the mobile platform 104 further includes a damping arrangement (as represented by reference numeral 130) based on a Stewart structure. The damping arrangement 130 is specifically engineered to address and mitigate high-frequency, low-amplitude disturbances, ensuring smooth operation and enhancing the user experience. FIGS. 1H and 1I illustrate detailed views of the damping arrangement 130, in accordance with one or more embodiments of the present disclosure. As illustrated, the damping arrangement 130 includes a first plate 132 and a second plate 134. It may be contemplated that the first plate 132 and the second plate 134 together forms the structure for the mobile platform 104. Herein, the first plate 132 and the second plate 134 are interconnected by a set of flexure units (generally represented by reference numeral 136). In the present configuration, the set of flexure units 136 includes six flexure units 136 arranged as the Stewart structure (like a rosette of six flexure entities). It may be understood that, as used herein, the flexure units 136 are components that allow for limited movement or flexibility between the interconnected elements. In the context of the damping arrangement 130, the flexure units 136 play a role in providing the desired damping characteristics. Further, by leveraging the Stewart structure-based design for arrangement of the flexure unit 136 in the damping arrangement 130, the haptic device 100 effectively neutralizes high-frequency, low-amplitude disturbances.
[0066] FIG. 1J illustrates a diagrammatic view of the flexure unit 136, in accordance with one or more embodiments of the present disclosure. Further, FIG. 1K illustrates a section view of the flexure unit 136, in accordance with one or more embodiments of the present disclosure. As shown in combination of FIGS. 1J and 1K, the flexure unit 136 includes a linear leaf-spring based flexure 140 (“flexure 140”) sandwiched between two notch joints 142, 144. The linear leaf-spring based flexure 140 is a thin, elongated component made of a flexible yet resilient material, and is designed to exhibit specific deformation characteristics when subjected to forces or disturbances. Due to its linear and leaf-like shape, this flexure 140 can undergo bending and twisting, allowing it to absorb and dissipate energy effectively. The notch joints 142, 144 have a recess or notch-like design to anchor the flexure 140 securely while permitting specific movements. These notch joints 142, 144 ensure that the flexure remains aligned and is allowed to move only in predetermined ways. This arrangement allows for a longitudinal rotational twist about the axis of the flexure unit 136. In simpler terms, when a disturbance impacts the damping arrangement, the flexure can not only bend but also twist along its length; and, in turn, provides the damping arrangement 130 having the rosette of six flexure units 136 arranged in a Stewart structure, with ability to reject high-frequency, low-amplitude disturbances in the haptic device 100.
[0067] It may be understood that the damping capability of the flexure units 136 is attributed to the intrinsic friction between the layers of the flexures 140, due to the leaf-based configuration. In some examples, the damping properties of the flexure units 136 may further be enhanced by filling the mobile platform 104 with a viscous medium. The presence of this viscous medium creates additional resistance to the movement of the flexures 140, further absorbing disturbance energy. Furthermore, the viscosity of the viscous medium can be varied to fine-tune the damping properties as per the design configuration and/or specific application requirements of the haptic device 100.
[0068] Referring now to FIG. 2, illustrated is a block diagram representation of a system 200 incorporating the haptic device 100 to control a robotic device 10, in accordance with one or more embodiments of the present disclosure. As shown, the system 200 includes a controller 210 working in conjunction with the haptic device 100 to control the robotic device 10. Specifically, the controller 210 is configured to translate the user interactions as control instructions for the robotic device 10. Herein, the robotic device 10 may include a set of end-effectors (not shown) adapted to replicate user movements based on the control instructions, and transmit haptic feedback signals corresponding to encountered resistances by the set of end-effectors to the controller 210. The controller 210, in turn, is configured to govern the set of rotary actuators 106 based on the haptic feedback signals, enabling a bi-directional communication between the user and the robotic device 10. It may be contemplated that, for this purpose, the haptic device 100 has exposed APIs to cater to communication with the controller 210 and/or the robotic device 10.
[0069] In a non-limiting configuration, the controller 210 may be integrated within the haptic device 100, as shown in FIG. 1E. In the said illustrated configuration, the controller 210 is shown to be disposed inside the base platform 102; however, it may be contemplated that the controller 210 may be located at some other location inside or even outside (exterior) of the haptic device 100 without any limitations. In an example, the controller 210, as used herein, is a BeagleBone® Blue controller as known in the art. In other examples, other types of controllers, such as Raspberry Pi, ODROID, etc. may be used. Such details for the controller 210 may be contemplated by a person skilled in the art and thus have not been discussed herein for brevity of the present disclosure.
[0070] More specifically, the controller 210 serves as an intermediately unit, translating the tactile interactions captured by the haptic device 100 into actionable commands for the robotic device 10. When a user interacts with the haptic device 100, it captures the details of the user interaction, from the force exerted to the direction of movement. Specifically, as the user interacts with the mobile platform 104 of the haptic device 100, any movement is directly converted to velocity of the mobile platform 104. The encoders, in the haptic device 100, are able to estimate the desired velocity the user wants to give to the robotic device 10 at the remote end. This data is then transmitted to the controller 210. The controller 210, equipped with specialized algorithms and logic, processes this data, interpreting the user interactions and generates specific commands tailored for the robotic device 10. These commands, based on the user interactions with the haptic device 100, instruct the robotic device 10 on actions it needs to undertake. Thereby, the robotic device 10 mirrors the user interactions as captured by the haptic device 100.
[0071] It may be appreciated that as the robotic device 10 manoeuvres within its environment, it might encounter various physical stimuli. These stimuli generate force-torque signals based on interactions of the robotic device 10, whether it's touching a solid object or responding to an external force. The controller 210 captures these force-torque signals and transmits them back to the haptic device 100 in the form of, for example, force component. The haptic device 100 converts these into a specific torque value. Once determined, this torque value is used to govern the rotary actuators 106 in the haptic device 100, creating a restrictive sensation, to provide a feedback force to the user at the manipulandum 126 which is consistent with the environmental interactions of the robotic device 100.
[0072] Thus, the system 200 of the present disclosure provides a synergy ensuring that user-robot interactions are intuitive, responsive, and immersive, bridging the gap between the user interactions at the haptic device 100 and actions of the robotic device 10.
[0073] Referring to FIG. 3, illustrated is a circuit diagram (as represented by reference numeral 300) of the system 200 incorporating the haptic device 100, in accordance with one or more embodiments of the present disclosure. The haptic device 100 primarily draws its energy from a power supply 302. In a nom-limiting embodiment, the power supply 302 may be a 120W, 24V @5A AC/DC adapter. This adapter is specifically chosen to ensure a steady and consistent 12V input supply, offering the necessary power to drive intricate mechanisms and electronic components of the haptic device 100. Further, a resettable fuse 304 made of polymeric PTC, rated at 24V and having a trip current of 6A, serves as a protective barrier against overcurrent situations. In the event of any unexpected current surge, the resettable fuse 304 will temporarily break the circuit, safeguarding the haptic device 100 from potential damage. Further, an overvoltage protection device 306 is incorporated into the haptic device 100 to ensure that even if an adapter delivers a voltage exceeding the specifications, the haptic device 100 remains shielded. Specifically, the overvoltage protection device 306 can handle voltages up to 110% of the rated voltage, providing a substantial safety margin. A circuit monitor 308 is utilized by the haptic device 100 to continuously monitor current, voltage, and power values. This constant surveillance ensures that the haptic device 100 operates within its specified parameters and can instantly respond to any anomalies. Further, a buck converter 310 in the form of DC/DC step down converter is employed which is tailored for the controller 220, to provide a rated voltage and current (such as, 12V, 1A). Further, the orientation and movement feedback mechanisms for the haptic device 100 are provided by the integrated IMUs (as represented by reference numeral 320A-D). Two pairs of IMUs, namely a first pair of IMU-1 320A and IMU-2 320B, and a second pair of IMU-3 320C and IMU-4 320D, are strategically placed on the haptic device 100, with the first pair being oriented at 90 degrees to each other on the base platform 102, while the second pair has a similar orientation on the mobile platform 104. This configuration ensures comprehensive and accurate capture of angular movements and positions of the haptic device 100.
[0074] Referring to FIG. 4, illustrated is a flow diagram representation of a method (as represented by reference numeral 400) of implementation of the haptic device 100, in accordance with one or more embodiments of the present disclosure. The present method 400 focuses on facilitating an intricate co-ordination between the user and the robotic device 10 using the haptic device 100. By establishing this bi-directional communication, the method 400 ensures an immersive and intuitive human-robot interaction experience. At step 402, the method 400 includes providing the haptic device 100 (as discussed in the preceding paragraphs). At step 404, the method 400 includes capturing, via the manipulandum 126, the user interactions with the haptic device 100. At step 406, the method 400 includes translating the captured user interactions into control instructions for the robotic device 10. At step 408, the method 400 includes receiving haptic feedback signals corresponding to encountered resistances by the set of end-effectors of the robotic device 10 while replicating user movements based on the control instructions. At step 410, the method 400 includes governing the set of rotary actuators 106 based on the haptic feedback signals, enabling a bi-directional communication between the user and the robotic device 10.
[0075] By solving the issues of singularity and constraint, the haptic device (100) with its refined arrangement of rotary actuators (106) opens-up possibilities for diverse applications, ranging from medical simulations to advanced gaming, where the traditional systems were impeded by their inherent limitations. The haptic device 100 of the present disclosure may have many applications:
Virtual Reality Game Engine Integration:
The haptic device 100 is capable of providing an actuation rate of at least 1000 Hz, enabling it to faithfully replicate interactions within a virtual environment, particularly within a game loop. Consider a scenario where a virtual object makes contact with a wall in a game setting. This collision would naturally result in a restriction or force exerted by the wall on the object. The haptic device 100, through its manipulandum 126, can simulate this force, allowing users to physically experience the virtual interaction. This can be used for training simulations, where tactile feedback can greatly enhance the learning experience.
Telerobotics:
The haptic device 100 finds many applications in telerobotics, specifically in the remote control of collaborative robots (Cobots). FIG. 5 illustrates a depiction of an exemplary implementation of the haptic device 100 in one of such scenarios, in accordance with one or more embodiments of the present disclosure. For instance, during a surgical procedure, a surgeon can utilize the haptic device 100 to guide a robotic arm. The haptic device 100 offers the surgeon a tangible sense of touch, mirroring the real-time interactions of the robot with its environment. Furthermore, the haptic device 100 proves invaluable in scenarios that pose risks to human safety. Operations like bomb disposal or drone manoeuvring can be executed remotely, with the haptic device 100 ensuring that the operator remains in a safe zone while still experiencing a realistic sense of touch.
Healthcare:
In the medical sector, the haptic device 100 addresses several complex challenges. The haptic device 100 offers clinicians, especially surgeons, a tangible sensation when they engage in rehabilitation procedures. This tactile feedback can be crucial in delicate operations where precision and responsiveness are paramount.
Research and Development:
For professionals working in research and development, especially those focusing on 3D environments, the haptic device 100 allows them to physically feel virtual objects, enhancing their understanding and interaction with these environments. This tactile interface can significantly boost the efficacy of their research endeavours.
Scientific Visualization:
The haptic device 100 stands out as a 3D input apparatus, especially in the field of scientific visualization. Through the haptic device 100, forces can be introduced, enabling users to gain a more profound and tangible understanding of scientific data. This becomes particularly useful in scenarios where visual data needs to be complemented with tactile feedback, ensuring a more comprehensive data interpretation process.
[0076] The haptic device 100 of the present disclosure provides a significant leap forward in tactile feedback systems. The haptic device 100, with its integration of sophisticated mechanical structures, ensures a high degree of fidelity in capturing and replicating user interactions. The haptic device 100 enhances user engagement, ensures safety, and offers a level of interaction that is both intuitive and immersive. By enabling users to physically feel and interact with virtual or distant environments, the haptic device 100 provides the potential of integrating human touch with technological advancements.
[0077] The foregoing descriptions of specific embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiment was chosen and described in order to best explain the principles of the present disclosure and its practical application, to thereby enable others skilled in the art to best utilize the present disclosure and various embodiments with various modifications as are suited to the particular use contemplated. , Claims:WE CLAIM:
What is claimed is:
1. A haptic device adapted to be operated as a 6DoF (degree-of-freedom) parallel manipulator, the haptic device comprising:
a base platform;
a mobile platform;
a set of rotary actuators arranged at the base platform and provided with a revolute joint; and
a plurality of legs flexibly connecting the mobile platform to the base platform, with each one of the plurality of legs comprising a crank coupled to the revolute joint of one of the set of rotary actuators and a first spherical joint, and a link coupled to the first spherical joint and a second spherical joint positioned at the mobile platform, wherein two proximate legs of the plurality of legs at the base platform diverge at the mobile platform.

2. The haptic device as claimed in claim 1, wherein each one of the sets of rotary actuators comprises at least one motor, such that the motors within the base platform are organized in pairs, with axes of adjacent motors in each of the pairs being coincident.

3. The haptic device as claimed in claim 2, wherein the set of rotary actuators comprises six rotary actuators, and wherein the motors are organized in three groups, and wherein the axes of the three groups are oriented 120 degrees apart from each other.

4. The haptic device as claimed in claim 2, wherein the motor is a brushless direct-current (BLDC) motor configured to generate high torque at low rotations per minute (RPM).

5. The haptic device as claimed in claim 1, wherein each one of the set of rotary actuators is attached to a spring for gravity balancing of the base platform.

6. The haptic device as claimed in claim 1, wherein the base platform forms a hexagon inscribed in a circle with a diameter in a range of 230 mm to 250 mm and the mobile platform forms a hexagon inscribed in a circle with a diameter in a range of 110 mm to 140 mm.

7. The haptic device as claimed in claim 1, wherein the link in each one of the plurality of legs has a length in a range of 160 mm to 200 mm and the crank in each one of the plurality of legs has a length in a range of 40 mm to 60 mm.

8. The haptic device as claimed in claim 1, wherein each of the first spherical joints and each of the second spherical joints is a ball and socket type joint having a cone angle limited to a range of 48 degrees to 62 degrees.

9. The haptic device as claimed in claim 1 further comprising a stopper associated with the revolute joint of each one of the set of rotary actuators to restrict motion range thereof.

10. The haptic device as claimed in claim 1 further comprising a manipulandum positioned on the mobile platform, wherein the manipulandum comprises a user interface mechanism configured to capture user interactions, and generate control signals to govern the set of rotary actuators based on the user interactions.

11. The haptic device as claimed in claim 1 further comprising an encoder associated with each one of the set of rotary actuators, and wherein the encoder is configured to detect a rotational position of the corresponding one of the set of rotary actuators.

12. The haptic device as claimed in claim 1 further comprising a first Inertial Measurement Unit (IMU) located on the base platform and a second IMU located on the mobile platform, and wherein the first and second IMUs are configured to measure angular readings corresponding to relative positioning of the mobile platform with respect to the base platform resulting from user interactions.

13. The haptic device as claimed in claim 1, wherein the mobile platform further comprises a damping arrangement based on a Stewart structure, and wherein the damping arrangement comprises a first plate and a second plate interconnected by a set of flexure units, and each one of the set of flexure units comprising a linear leaf-spring based flexure sandwiched between two notch joints, allowing a longitudinal rotational twist about axis of corresponding one of the set of flexure units, to reject high-frequency, low-amplitude disturbances.

14. A system comprising:
a haptic device comprising:
a base platform;
a mobile platform;
a set of rotary actuators arranged at the base platform and provided with a revolute joint;
a plurality of legs flexibly connecting the mobile platform to the base platform, with each one of the plurality of legs comprising a crank coupled to the revolute joint of one of the set of rotary actuators and a first spherical joint, and a link coupled to the first spherical joint and a second spherical joint positioned at the mobile platform, wherein two proximate legs of the plurality of legs at the base platform diverge at the mobile platform;
a manipulandum positioned on the mobile platform, wherein the manipulandum comprises a user interface mechanism configured to capture user interactions; and
a controller configured to translate the user interactions as control instructions for a robotic device,
wherein the robotic device comprises a set of end-effectors adapted to replicate user movements based on the control instructions, and transmit haptic feedback signals corresponding to encountered resistances by the set of end-effectors to the controller, and
wherein the controller is configured to govern the set of rotary actuators based on the haptic feedback signals, enabling a bi-directional communication between the user and the robotic device.

15. A method comprising:
providing a haptic device comprising: a base platform; a mobile platform; a set of rotary actuators arranged at the base platform, each actuator having a revolute joint; a plurality of legs connecting the mobile platform to the base platform, wherein each leg comprises a crank connected to the revolute joint of an associated rotary actuator and a first spherical joint, and a link coupled between the first spherical joint and a second spherical joint located at the mobile platform; and a manipulandum on the mobile platform, configured to capture user interactions;
capturing, via the manipulandum, user interactions with the haptic device;
translating the captured user interactions into control instructions for a robotic device;
receiving haptic feedback signals corresponding to encountered resistances by a set of end-effectors of the robotic device while replicating user movements based on the control instructions; and
governing the set of rotary actuators based on the haptic feedback signals, enabling a bi-directional communication between the user and the robotic device.