DESC:RELATED PATENT APPLICATION(S):
This application claims the priority to and benefit of Indian Provisional Patent Application No. 202341055758 filed on August 21, 2023; the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the technical field of assistive technologies which are used to enhance the functioning and independence of an individual. Particularly, the invention relates to a customizable and responsive sit/stand assistance device to assist during all phases of stand-to-sit and sit-to-stand maneuvers.

BACKGROUND OF THE INVENTION

At present, the sit-to-stand maneuver of an individual involves the combined action of a forward rotation, rise, and balance. Normal sit-to-stand maneuver has four stages. The first, called flexion-momentum, involves the forward rotation of the torso, to generate momentum. The second stage, called balancing, is characterized by the forward rotation of the tibial segment of the leg concerning the foot, ending at maximum ankle dorsiflexion. The first two stages help lift the body’s center of mass to initiate rise. The third stage, called extension or the rising stage, comprises the synchronized rotation about the ankle, knee, and hip, ending with the body’s erection to a full-upright position. The fourth stage is that of stabilization to a position of standing.

STS (sit to stand/stand to sit) is among the most important markers of functional independence in humans. The ability to perform this function decreases in certain individuals, due to various reasons ranging from old age, disorders such as muscular dystrophy, reduced bone density, arthritis, etc. There exist a few assistive devices that are designed to aid in such cases. Exoskeletons are suitable for cases that require prolonged assistance and rehabilitation but are tedious to wear and remove. Lift chairs such as those provided by Pride Mobility, Golden Technologies, and Mega Motion among others are specialized furniture replacements that can help users to sit down and stand up but are bulky and expensive.

Compact alternatives do exist, which are small enough to externally append onto existing furniture but fail to aid in the final stages of sit-to-stand (and early stages of stand-to-sit). Moreover, most existing solutions require electrical power to perform their function as a result they cannot be used in places where the power supply is interrupted due to safety concerns, relying on batteries also comes with its own set of uncertainties and therefore is limited by accessibility. Furthermore, none of these systems provide customizability of the trajectory and force profile to fit the requirements of a user. A few passive systems that utilize spring-loaded or cable-driven lifts are used in hospitals and palliative care centers, but they require a skilled care provider to operate.

Some of the existing prior arts disclosing the assistive mechanism are given below:

US Patent No. US10874565B2 discloses a patient assisting system including a frame having a sling assembly attachment point and a lifting arm which is movable relative to the frame, and which includes a receptacle. When the sling assembly is attached to the attachment point and extends through the receptacle, a portion of the sling travels through the receptacle as the lifting arm moves relative to the frame. Another embodiment includes exactly one four bar linkage comprised of a frame having an attachment point for a sling assembly, a lifting arm having a receptacle, a lower cross arm and an upper cross arm. The lifting arm is adapted to be movable between a person seated position and a person-standing position. The receptacle is located along the lifting arm so that motion of the lifting arm causes the receptacle to move along a curved path having a concave side which is person-facing.

US Patent No. US7540045B2 discloses an apparatus for assisting a person to stand. The apparatus comprises a mobile support structure, a pulley system, a counterbalance weight and a harness. The counterbalancing weight is coupled to the pulley system and the harness, which is coupled to the person being assisted in standing. The apparatus may also comprise a leg brace, a handle and wheel assemblies.

However, the existing prior arts discloses lift chair or assisting devices which are bulky and expensive due to lot of components forming a complex structure. Compact alternatives are available, which are small enough to externally append onto existing furniture but fail to aid in the final stages of sit-to-stand (and early stages of stand-to-sit. Further, the prior arts require electrical power to perform their function as a result they cannot be used in places where the power supply is interrupted. Furthermore, none of these systems provide customizability of the trajectory and force profile to fit the requirements of a user.

Therefore, there is a need to develop a customizable and responsive mechanism for a chair to assist during all phases of stand-to-sit and sit-to-stand maneuvers. There is a need of mechanism which is a compact mechanical solution that can be seamlessly integrated with ordinary seating furniture such as chairs or sofas. It can assist users up to the final stage of standing, without needing another human’s assistance and it can be customized to fit the user’s requirements.

Limitations of known art:
1. Dependence on electrical power: Existing solutions that comprise the state of the art are powered by electrical connections or battery packs. This limits the usage time, deployment environments (given the availability of electrical connection points and safety risks associated).
2. Customizability: While electronically enabled solutions that exist account for differences in user requirements through active sensing, passive solutions have to rely on physical adjustments prior to usage. The extent of these customizations is limited to force characteristics.
3. Retrofit ability: The existing solutions are either packed along with chairs/sofas or sold as add on’s to place above existing chairs/sofas and not allowed for integration with market available seating furniture with a minimal footprint.
4. STS Motion Trajectory: Most existing solutions attempt to account for the required force characteristics of sit to stand (or vice versa) as is available in biomechanical literature, only a few account for the path profile that is followed by the user – and these are bulky and need to be used, stored and maintained as separate appliances altogether.
5. Mechanical Classification of intent: When the activity starts, the mechanism needs to be activated explicitly, i.e., with a switch or with a knob in the case with the state of the art.

The present invention provides a customizable and responsive mechanism for a chair. In particular, the present invention is a passive assistive medical device that is designed to support all the phases of sit-to-stand and stand-to-sit maneuvers without relying on electrical actuators, electronic sensing, or control mechanisms, thereby enhancing the functioning and independence of an individual who has the reduced ability to perform STS (sit to stand/stand to sit). The chair consists of open-circular cross-section shells that bend and twist to provide customized torque-angle characteristics with negative stiffness and bi-stability features and a gas spring (3) that help to support the individual in all phases of STS. The passive chair incorporates mechanical programmable smartness, enabling it to assess the user's intent as estimated from the characteristic dynamics of STS (sit to stand/stand to sit) motion. This capability allows the chair to respond intelligently and adaptively based on the user's movements and intentions. The chair is highly customizable to meet the specific user's requirements. It achieves this by allowing adjustable mechanical dimensions, accommodating individual needs. Additionally, it can adapt to different users’ requirements within the same configured setting, providing a range of torque profiles and trajectories to cater to varying preferences and demands. The mechanism can be easily integrated with seating furniture both in public and private settings such as chairs, sofas, and commodes.

OBJECTS OF THE INVENTION:

A primary object of the present invention is to provide a customizable and responsive sit-to-stand (STS) and back-to-sit (BTS) assistance device.

Another object of the present invention is to provide a customizable and responsive mechanism for a chair/sofa or commode to assist during all phases of stand-to-sit (STS) and sit-to-stand (STS) maneuvers.

Another object of the present invention is to provide an sit-to-stand (STS) and back-to-sit (BTS) assistance device having a mechanical solution that assists with sitting down and standing up without the need for electrical actuation or electronic sensing or control.

Another object of the present invention is to provide a customizable mechanism that can adapt to different users' requirements within the same configured setting, providing a range of torque profiles and trajectories to cater to varying preferences and demands.

Another object of the present invention is to provide assistive medical devices which are used to enhance the functioning and independence of an individual and to enable individuals to maintain or improve their well-being and quality of life by providing support, assistance, or compensation for specific impairments.

Another object of the present invention is to provide device with assistive mechanism which is responsive with its capability to gauge the user intent, as estimated from the characteristic dynamics of STS motion.

Another object of the invention is to provide the customizable and responsive sit-to-stand (STS) and back-to-sit (BTS) assistance device consists of open-circular cross-section shells that bend and twist to achieve customized torque-angle characteristics with negative stiffness and bi-stability features and a gas spring (3) that help to support the individual in all phases of STS.

Another object of the present invention is to provide an easy-to-use, passive, purely mechanical actuator design of an assisting device that offers significant advantages wherein the lack of electrical power enables wider usability of the device, in environments with increased levels of moisture such as washrooms or open-air settings such as bus stations and other public spaces.

Another object of the present invention is to provide a device with assistive mechanism which is a compact mechanical solution that can be seamlessly integrated with seating furniture both in public and private settings such as chairs, sofas, and commodes.

Another object of the present invention is to provide an assistive device that can assist users up to the final stage of standing, without needing another human’s assistance and it can be customized to fit the user’s requirements.

Yet another object of the present invention is to provide a responsive device, where responsiveness is achieved by the sequence of two-degree-of-freedom (2-DoF) linkage, torque-and-trajectory-customizable, and comprehensively assistive solution to the problem of sit-to-stand and stand-to-sit (STS).

SUMMARY OF THE INVENTION:
The primary aspect of the present invention is to provide a customizable and responsive sit-to-stand (STS) and back-to-sit (BTS) assistance device comprising:
a) a sequence of two-degree of freedom (2-DOF) system;
b) a compliant hinge (2);
c) a pneumatic strut (3);
d) a pair of cams mounted on top of the compliant hinge (2) as a holding means which allows a provision for tunable torque profiles; and
e) a means for holding the device rigidly at the ends, even with minimal footprint;
wherein, the unique mechanism of compliant hinge (2) and gas spring of 2-DOF system supports all the four phases of sit-to-stand or back-to-sit maneuvers, and during all body-extension and stabilization phases.

In one aspect of the present invention discloses a sequence of two-degree of freedom (2-DOF) system is enabled by passive mechanical actuators.

In one aspect of the present invention discloses a 2-DOF system allows responsiveness and is provided with a typical trajectory linkage mounted as floating atop of compliant hinge

In one aspect of the present invention discloses a compliant hinge (2) of 2-DOF system having open-circular cross-section shells, bend and twist to provide customized torque-angle characteristics with negative stiffness and bi-stability features, thereby the device is customizable within a range of torque profiles and trajectories.

In one aspect of the present invention discloses a 2-DOF system is provided with a typical trajectory linkage mounted as floating atop of compliant hinge that is further separated into a four bar linkage and a slider crank mechanism, with the crank and slider segments of the latter extended from the coupler and rocker segments of the former respectively, and is responsible for the characteristic trajectory with in-situ adjustment.

Another aspect of the present invention discloses the compliant hinge is an optimized weight and assembly with open-circular cross-section shells which allows tunable torque profiles with replacement of a cam components.

Another aspect of the present invention discloses a pneumatic strut (gas spring) (3) is a passive provision for segment adjustments which permits the gas spring linage to hinge at an appropriate distance from the common rotation joint to offer different torque profiles serve same geometric configuration for multiple users.

Another aspect of the present invention discloses a pneumatic strut is independently connected to four bars between the compliant hinge and rocker.
Yet another aspect of the present invention discloses device is mechanically programmable for recording altered responsiveness, where the extent and nature responsiveness of the device is carried out by changing the cam profile and the dimensions of the gas spring mounting location based on recognition of user’s intent, or behavior or movements or attempt, by estimating characteristic dynamics of sit to stand or back to sit motion.
Another aspect of the present invention discloses a pair of cams are replaceable to account specific torque profile requirement of the user.

Another aspect of the present invention discloses a device is operated passively without any supportive electrical actuators, electronic sensing or control mechanisms.

Another aspect of the present invention discloses a device further comprising an adjustable frame (1).

Another aspect of the present invention discloses a device can be made of metals and non-metallic (plastic) materials or combinations thereof.

Another aspect of the present invention discloses mechanical actuators of device are compliant hinge (2) and a pneumatic strut (gas spring) (3), which can be optionally replaced with power-assisted mechanisms such as supportive electrical or electronic actuators, or control mechanisms.

Another aspect of the present invention discloses a device can be retrofitted with available seating furniture with a minimal footprint, both in private (commode) and public seating (chair/sofa).

BRIEF DESCRIPTION OF THE DRAWINGS
The drawings described herein are intended to provide a further understanding of the invention and are intended to be a part of the invention. However, the drawings as shown are representative and non-limiting the scope of the invention. In the drawings:

Figure 1a & 1b: Illustrates lateral views of sit-to-stand (STS) and back-to-sit (BTS) assistance device (100).

Figure 2: Illustrates a top view of device.

Figure 3: Illustrates is the Four Phases of stand-to-sit motion, 1) Flexion-momentum, 2) Balancing, 3) Extension, and 4) Stabilization.

Figure 4: Illustrates the schematic diagram of the mechanism showing the passive mechanical actuators, compliant hinge (2), and gas spring (3).

Figure 5: Illustrates the kinematic representation of the mechanism illustrating the linkages in the mechanism, seat segment (S1S2), seat-crank (O2R), slider-crank linkage (RS1S2), gas spring linkage (O2L1L2), seat slider (RS2).

Figure 6a & 6b: Illustrates the side views of the computer aided design (CAD) model of device illustrating the provision provided in the mechanism for adjustable segment length.

Figure 7: Illustrates the schematic lifting path of device.

Figure 8: Illustrates the provision provided in the mechanism to vary the lower segment (O2L1) length within the same mechanism.

Figures 9: Illustrates the means of holding of device.

Figure 10: Illustrates the effective torque envelope as experienced by the seat crank segment (O2R) by varying the length of segment (O2L1).

Figure 11: Illustrates the envelope of path trajectories for various values of spring constant (K2) plotted for the midpoint of the seat segment S1S2 (s = S1S2/2).

Figure 12: Illustrates the envelope of path trajectories for various values of damping coefficient (c) plotted for the midpoint of the seat segment S1S2 (s = S1S2/2).

Figure 13: Illustrates the plot of Electromyography (EMG) data collected from the Preliminary testing of the prototype from the sitting posture to standing by a healthy volunteer with EMG sensors showing diminished muscle effort with assistance.

DESCRIPTION OF THE INVENTION

The main embodiment of the invention relates to a customizable and responsive sit-to-stand (STS) and back-to-sit (BTS) assistance device comprising:
i) a sequence of two-degree of freedom (2-DOF) system;
ii) a compliant hinge (2);
iii) a pneumatic strut (3);
iv) a pair of cams mounted on top of the compliant hinge (2) as a holding means which allows a provision for tunable torque profiles; and
v) a means for holding the device rigidly at the ends, even with minimal footprint;
wherein, the unique mechanism of compliant hinge (2) and gas spring of 2-DOF system supports all the four phases of sit-to-stand or back-to-sit maneuvers, and during all body-extension and stabilization phases.

Accordingly, the present invention discloses the device has a sequence of two-degree of freedom (2-DOF) system is enabled by passive mechanical actuators.

Accordingly, the present invention discloses the device with 2-DOF system allows responsiveness and is provided with a typical trajectory linkage mounted as floating atop of compliant hinge.

Accordingly, the present invention discloses the compliant hinge (2) of 2-DOF system having open-circular cross-section shells, bend and twist to provide customized torque-angle characteristics with negative stiffness and bi-stability features, thereby the device is customizable within a range of torque profiles and trajectories.

Accordingly, the present invention discloses the 2-DOF system is provided with a typical trajectory linkage mounted as floating atop of compliant hinge that is further separated into a four bar linkage and a slider crank mechanism, with the crank and slider segments of the latter extended from the coupler and rocker segments of the former respectively, and is responsible for the characteristic trajectory with in-situ adjustment.

Accordingly, the present invention discloses a compliant hinge is an optimized weight and assembly with open-circular cross-section shells which allows tunable torque profiles with replacement of a cam components.

Accordingly, the present invention discloses pneumatic strut (gas spring) (3) is a passive provision for segment adjustments which permits the gas spring linage to hinge at an appropriate distance from the common rotation joint to offer different torque profiles serve same geometric configuration for multiple users.

Accordingly, the present invention discloses device the pneumatic strut is independently connected to four bars between the compliant hinge and rocker.

Accordingly, the present invention discloses device is mechanically programmable for recording altered responsiveness, where the extent and nature responsiveness of the device is carried out by changing the cam profile and the dimensions of the gas spring mounting location based on recognition of user’s intent, or behavior or movements or attempt, by estimating characteristic dynamics of sit to stand or back to sit motion.

Accordingly, the present invention discloses the pair of cams are replaceable to account specific torque profile requirement of the user.

Accordingly, the present invention discloses the device is operated passively without any supportive electrical actuators, electronic sensing or control mechanisms.

Accordingly, the present invention discloses the device further comprising an adjustable frame (1).

Accordingly, the present invention discloses the device can be made of metals and non-metallic (plastic) materials or combinations thereof.

Accordingly, the present invention discloses the mechanical actuators of device are compliant hinge (2) and a pneumatic strut (gas spring) (3), which can be optionally replaced with power-assisted mechanisms such as supportive electrical or electronic actuators, or control mechanisms.

Accordingly, the present invention discloses the device can be retrofitted with available seating furniture with a minimal footprint, both in private (commode) and public seating (chair/sofa).

A mechanical system designed to assist individuals with the actions of sitting down and standing up from chairs, particularly for those with diminished ability due to age, illness, injury, or other conditions. This mechanism operates without the need for an external power source such as electricity or batteries, and it does not require active control components like motors, sensors, or microprocessors. This make it suitable for use in environments where electrical power is unavailable, unreliable, or unsafe, such as remote locations or moisture-prone areas like bathrooms, parks, or outdoor settings.

The mechanism is intelligently designed to be passively responsive, adjusting to the user’s specific needs based on their weight, height, and other biomechanical factors. It can also interpret the user’s intentions by analyzing the dynamics of their movement when transitioning from STS (Sit-To-Stand) and BTS (Back-To-Sit). The design is customizable to individual requirements through adjustable mechanical parameters, and once set, its 2-degree-of-freedom (2 - DOF) structure can accommodate a variety of users within a range of torque profiles and movement paths.

The system is engineered to provide support throughout all four phases of sit-to-stand and stand-to-sit motions, addressing a gap in existing assistive devices that often fail to offer adequate support during the body-extension and stabilization phases of the sit-to-stand maneuver. The apparatus features a serial 2 – DOF system driven by passive mechanical actuators. The first actuator is a compliant hinge (2), made from open section shells that flex and twists to deliver customized torque-angle characteristics, including negative stiffness and bi – stability. The second actuator is pneumatic strut or gas spring (3), though alternative actuators – whether passive, active, mechanical, or electrical – can be integrated to achieve the desired motion. Additionally, the mechanism is designed to be retrofittable, meaning it can be easily installed onto any suitable seating furniture due to its minimal mounting requirements.

STS (sit to stand/stand to sit) is among the most important markers of functional independence in humans. The ability to perform this function decreases in certain individuals, due to various reasons ranging from old age, disorders such as muscular dystrophy, reduced bone density, arthritis, etc. There exist a few assistive devices that are designed to aid in such cases. Exoskeletons are suitable for cases that require prolonged assistance and rehabilitation but are tedious to wear and remove. Lift chairs such as those provided by Pride Mobility, Golden Technologies, and Mega Motion among others are specialized furniture replacements that can help users sit down and stand up but are bulky and expensive.

Compact alternatives do exist, which are small enough to externally append onto existing furniture but fail to aid in the final stages of sit-to-stand (and early stages of stand-to-sit). Moreover, most existing solutions require electrical power to perform their function as a result they cannot be used in places where the power supply is interrupted due to safety concerns, relying on batteries also comes with its own set of uncertainties and therefore is limited by accessibility. Furthermore, none of these systems provide customizability of the trajectory and force profile to fit the requirements of a user. A few passive systems that utilize spring-loaded or cable-driven lifts are used in hospitals and palliative care centers, but they require a skilled care provider to operate.

Accordingly, the present invention provides a customizable and responsive mechanism for a chair to assist during all phases of stand-to-sit and sit-to-stand maneuvers. In particular, the present invention provides an easy-to-use, passive, purely mechanical design that offers significant advantages. For example, the lack of electrical power enables wider usability of the device, in environments with increased levels of moisture such as washrooms or open-air settings such as bus stations and other public spaces. Waterproofing of electrical components would become a necessity – regulatory in certain cases – to ensure safe usage, as opposed to a mechanical solution which would not require any environment-related function and safety requirements. The mechanism is a compact mechanical solution that can be seamlessly integrated with seating furniture both in public and private settings such as chairs, sofas, and commodes. It can assist users up to the final stage of standing, without needing another human’s assistance. Furthermore, it can be customized to fit the user’s requirements.

More particularly, the present invention provides an assistive mechanism, which is a mechanical solution that assists with sitting down and standing up. The same has been achieved without the need for electrical actuation or electronic sensing or control. The passive design is capable of mechanically programmable smartness to gauge the user’s intent, as estimated from characteristic dynamics of STS (sit to stand/stand to sit) motion. The design is customizable to the specific user’s requirements by configuring adjustable mechanical dimensions but also adjusts to different users’ requirements (while in the same configured setting) within a range of torque profiles and trajectories. The mechanism is designed such that it provides the necessary support in all the phases of sit-to-stand and stand-to-sit maneuvers unlike most of the existing assistive devices which do not provide support during the body-extension and stabilization phases of sit-to-stand maneuver.

The apparatus consists of a serial two-degree-of-freedom (2 - DOF) system enabled by passive mechanical actuators – the first, a compliant hinge (2) developed from open section shells that bend and twist to provide customized torque-angle characteristics with negative stiffness and bi-stability features, and the second, a pneumatic strut. The lack of electrical energy in the system allows for deployment in otherwise regulated environments such as washrooms, given their moisture content. However, the design may further incorporate as replacements alternate actuators – passive/active, mechanical/electrical – to enable the configured motion.

The primary aspect of the present invention is to provide a customizable and responsive mechanism for a chair to assist during all phases of stand-to-sit and sit-to-stand manoeuvre.

In one aspect of the present invention, the invention provides a customizable and responsive mechanism to be fitted in devices such as chairs, sofas and commodes which is used to enhance the functioning and independence of an individual. These devices along with the responsive mechanism enable individuals to maintain or improve their well-being and quality of life by providing support, assistance, or compensation for specific impairments.

Figures 1-2 shows the prototype images of responsive mechanism (100) and the same fitted into a chair frame (200) respectively. In particular, Figure 1 shows only the fabricated mechanism (100) to be fitted in devices to assist during all phases of stand-to-sit and sit-to-stand manoeuvre. Figure 2 shows the mechanism (100) of the present invention fitted into a chair frame (200).

Figure 3 shows four phases of stand-to-sit (STS) motion. The sit-to-stand manoeuvre of an individual involves the combined action of a forward rotation, rise, and balance, as particularly shown in Figure 3. Normal sit-to-stand manoeuvre has four stages. As shown in Figure 3, the first phase 1, called flexion-momentum, involves the forward rotation of the torso, to generate momentum. The second stage 2, called balancing, is characterized by the forward rotation of the tibial segment of the leg concerning the foot, ending at maximum ankle dorsiflexion, as shown in Figure 3. The first two stages help lift the body’s centre of mass to initiate rise. As shown in Figure 3, the third stage 3, called extension or the rising stage, comprises the synchronized rotation about the ankle, knee, and hip, ending with the body’s erection to a full-upright position. The fourth stage 4 is that of stabilization to a position of standing as shown in Figure 3.

Figure 4 shows the schematic diagram of the mechanism. In particular, the mechanism as shown in Figure 4 shows the passive mechanical actuators, frame (1), compliant hinge (2), gas spring (3), revolute joint (4), seat (5) and slider joint (6). Further, Figure 5 shows the kinematic representation of the mechanism illustrating the linkages in the mechanism, seat segment (S1S2), seat-crank (O2R), slider-crank linkage (RS1S2), gas spring linkage (O2L1L2), seat slider (RS2).

The present invention provides a responsive two-degree-of-freedom (2-DoF) linkage to provide a mechanically actuated, torque-and-trajectory-customizable, and comprehensively assistive solution to the problem of sit-to-stand and stand-to-sit (STS) motion, as schematically shown in Figure 4. The mechanism contains a linkage that is responsible for the characteristic trajectory, mounted as floating atop a compliant hinge (2). The linkage can further be separated into a 4-bar linkage and a slider crank mechanism, with the crank and slider segments of the latter extended from the coupler and rocker segments of the former, respectively. The four-bar is independently connected with a passive, but responsive pneumatic member coupled between the base segment as rigidly attached to a compliant hinge (2) and the rocker, shown in Figure 4.

The compliant hinge (2) is a weight and assembly optimized which allows for tunable torque profiles with the replacement of a cam component. The gas-spring member (3) can be hinged at appropriate distances from the common rotation joint to provide different torque profiles, peaking at required effective torque values. Furthermore, each of the revolute joints (4) can be adjusted along the lengths of their adjacent segments to provide an appropriate envelope of end-effector (i.e., the seat trajectories). These provisions to adjust torque and trajectory allow for mass customization towards maximizing mechanical efficacy and consequently minimizing the effort required to be put in by the user.

Given the 2-DoF nature of the mechanism, the same geometric configuration can lead to varying responses in terms of force and trajectory. This allows different users to concurrently use the mechanism given a fixed configuration of segment lengths, with varying levels of assistance. This proves beneficial in a deployment environment with limited access to repeated adjustments. Taking advantage of the characteristic dynamics of the first phase of sit-to-stand, wherein the torso moves forward thus moving the effective center of pressure (CoP, as shown in Figure 4) forward, the stiffness profiles of the compliant hinge (2) and pneumatic member can be adjusted to achieve sequential activation of the 2-DoF. This provides the ability to roughly characterize the motion of the user into ‘seated’, ‘moving arbitrarily’, and ‘moving with the intent to stand up’ – therefore enabling a responsive device without the use of active sensing.

When the user sits on the seat link (S1S2), the resultant response is felt as a transmitted combination of the responses of the compliant hinge (2) and gas spring (3), each of which can be adjusted to the user. During STS, the initial few degrees of travel as initiated by the user determine the manner of this response in the remaining cycle. This can be considered as a recognition of intent, whereby the dynamics of a user’s behaviour when attempting to sit down or stand up can be classified distinctly from that of their otherwise arbitrary movements. The minimized footprint of the mounting allows for easy attachment to various pieces of furniture, such as chairs or sofas, enabling seamless integration with a wide range of such amenities in both private and public settings.

Fig. 5 is the side view of the CAD model of the mechanism illustrating the provision provided in the mechanism for adjustable segment length. This allows for the adjustment of the revolute joints along the length of their adjacent segments which helps to achieve an appropriate envelope of end-effector (seat) trajectories. Also, the gas-spring member can be hinged at the appropriate distances from the common rotation joint which offers different torque profiles. These provisions to adjust torque and trajectory allow for mass customization towards maximizing mechanical efficacy and consequently minimizing the effort required to be put in by the user.
Fig. 6 visualizes the difference in paths traversed by the hip joint of the user when sitting down and standing up from an ordinary chair (first image), from a merely-pivoting assistive chair (second image), and the mechanism (third image). It can be observed that the while the existing products only function partly within a range of travel, they also move along simple rotational trajectories. However, naturally performed sit-to-stand and stand-to-sit maneuvers are characterized by complex and varying path trajectories. The same can be accounted for by the mechanism, ensuring continued assistance to the user into the later phases of sit-to-stand (and earlier phases of stand-to-sit).

Fig. 7 is the kinematic representation of the mechanism illustrating the linkages in the mechanism, seat segment (S1S2), seat-crank (O_2 R), slider-crank linkage (RS1S2), gas spring linage (O_2 L_1 L_2), seat slider (RS_2).

Fig. 8 shows the provision provided in the mechanism to vary the lower segment (O_2 L_1 ) length within the same mechanism. The mechanism is kinetoelastically constrained by the forces generated by the gas spring and the compliant hinge mechanism. The resultant trajectory is dependent on the stiffnesses of each, and more specifically, changes its behaviour based on the instantaneous ratios of their values. The length of segment O_2 L_1 can be adjusted (as shown in the figure) to achieve varying torque profiles.

Fig. 9 shows the effective torque envelope as experienced by the seat crank segment (O_2 R) by varying the length of segment O_2 L_1.

Fig. 10 is the envelope of path trajectories for various values of spring constant (K2) plotted for the midpoint of the seat segment S1S2 (s = S1S2/2).

Fig. 11 is the envelope of path trajectories for various values of damping coefficient (c) plotted for the midpoint of the seat segment S1S2 (s = S1S2/2).
Fig. 12(a), 12(b), and 12(c) show the stages of the mechanism visualized by a user’s sit-to-stand activity.

Fig. 13 is the plot of EMG data collected from the Preliminary testing of the prototype from the sitting posture to standing by a healthy volunteer with EMG sensors showing diminished muscle effort with assistance. This implies a reduction of effort on the subject’s part, in standing up from a chair given that they are assisted by the presented mechanism

The side view of the computer aided design (CAD) model of the mechanism illustrating the provision provided in the mechanism for adjustable segment length. This provision in the mechanism allows for the adjustment of the revolute joints (4) along the length of their adjacent segments which helps to achieve an appropriate envelope of end- effector (seat) trajectories. Also, the gas-spring member (3) can be hinged at the appropriate distances from the common rotation joint which offers different torque profiles. These provisions to adjust torque and trajectory allow for mass customization towards maximizing mechanical efficacy and consequently minimizing the effort required to be put in by the user.

The visualization of the difference in paths traversed by the hip joint of the user when sitting down and standing up from an ordinary chair (first image (a)), from a merely pivoting assistive chair (second image (b)), and the mechanism (third image (c)). It can be observed that while the existing products only function partly within a range of travel, they also move along simple rotational trajectories. However, naturally performed sit-to-stand and stand-to-sit maneuvers are characterized by complex and varying path trajectories. The same can be accounted for by the mechanism, ensuring continued assistance to the user into the later phases of sit-to-stand (and earlier phases of stand-to-sit).

Figure 8 shows the provision provided in the mechanism to vary the lower segment (O2L1) length within the same mechanism. The mechanism is kineto-elastically constrained by the forces generated by the gas spring (3) and the compliant hinge (2) mechanism. The resultant trajectory is dependent on the stiffnesses of each, and more specifically, changes its behaviour based on the instantaneous ratios of their values. The length of segment O2L1 can be adjusted (as shown in the figure 5) to achieve varying torque profiles.

Figures 9(a), 9(b), and 9(c) show the stages of the mechanism visualized by a user’s sit-to-stand activity.

Figure 10 shows the effective torque envelope as experienced by the seat crank segment (O2R) by varying the length of segment (O2L1). Figure 11 shows the envelope of path trajectories for various values of spring constant (K2) plotted for the midpoint of the seat segment S1S2 (s = S1S2/2). Figure 12 shows the envelope of path trajectories for various values of damping coefficient (c) plotted for the midpoint of the seat segment S1S2 (s = S1S2/2).

Figure 13 shows the plot of Electromyography (EMG) data collected from the Preliminary testing of the prototype from the sitting posture to standing by a healthy volunteer with EMG sensors showing diminished muscle effort with assistance. This implies a reduction of effort on the subject’s part, in standing up from a chair given that they are assisted by the presented mechanism.

Given the unique nature of human bodies, people tend to differ in their STS behavior. These differences can be accounted for by collecting a few information parameters such as biomechanical dimensions (weight, height), physiological conditions (disorders, discomforts, diseases, age) etc. in order to ascertain the best fit of the force and path trajectories of their sitting and standing motions.

While most existing solutions attempt to account for the required force characteristics of sit to stand (or vice versa) as is available in biomechanical literature, only a few account for the path profile that is followed by the user – and these are bulky and need to be used, stored and maintained as separate appliances altogether. This invention not only accounts for the natural profiles traced by the users’ center of masses but distinctly allows for adjustment of the same for different users – while being integrated seamlessly into existing furniture. This is achieved either as a preset adjustment to the available dimensional options during assembly or as DIY adjustments on the user’s end. Further, in the same configuration, the relative lack of rigidity given the 2-degree-of-freedom nature of the mechanism allows for in situ adjustment within a range.

A coupled slider crank and four-bar linkage floating atop a compliant hinge (2) –This mechanical setup allows for kineto-elastically linked but distinct degrees of freedom, which further allows for an extent of ‘smartness’ implemented in the device – mechanically itself. The resultant behavior of the mechanism allows for intent classification. While sitting, there is no force exerted on the user. Once stood up completely, there is no force exerted on the user. However, during this activity of going from the former to the latter, forces are applied by the requirements of STS dynamics, which are available in the literature and can be adjusted according to the user’s inputs. When the activity starts, need not to be activated explicitly, i.e., with a switch or with a knob (as is the case with the state-of-the-art. In the present invention, the user needs only to intend to stand up (or sit down and initiate the same activity naturally (in their body and the mechanism responds by assisting them along the configured trajectory – reducing the effort all along (measurable as MC – metabolic cost reduction).

The present invention provides a customizable and responsive mechanism for a chair to assist during all phases of stand-to-sit and sit-to-stand. In particular, the present invention introduces a user-friendly, passive, and entirely mechanical design, offering notable advantages. For instance, the absence of electrical power expands the device’s applicability, making it suitable for environments with heightened moisture levels like washrooms, or outdoor locations such as bus stations and public spaces. Unlike electrical alternatives that demand waterproofing to meet safety regulations, the mechanical approach eliminates this need, simplifying function and safety considerations. This compact mechanism seamlessly integrates with various seating furniture, both in public and private contexts such as chairs, sofas, and commodes. It provides assistance until the final stage of standing without external aid and can be tailored to individual user preferences.

Market avenues for this product can be broadly categorized into two sets: mass customizable deployments and median adjusted deployments. The first set focuses on a customer base of private individuals – to whose requirements the torque profile can be adjusted upon feedback from a pre-delivery interaction session. This involves gauging of the specific customer’s body characteristics and relevant physiological information to optimize the chair to suit them best (via data collected from predefined test paradigms and interviews during the pre-delivery interaction). The second set extends this facility to community spaces – both public and private (for instance, waiting areas/rooms/lounges at hospitals/banks/stations/airports, office spaces, parks, etc.). This is achieved by applying statistical medians of the subject population expected at the specific community space, to the torque characteristics and other ergonomic requirements of the chair. With the present invention, the following are implementable:

(a) Improved cataloguing of torque and trajectory characteristics for more specific use cases (examples, for specific disorders such as muscular dystrophy).
(b) Prognostic paradigms for predicting disorders via corollaries of developed STS profiles – allowing for non-invasive early indication of certain physiological conditions.

The product relies on a mechanism that foregoes the requirement of continuous or stored electrical power, thereby allowing versatility of deployable environments – for example, both urban and rural, etc. Furthermore, the product enables increased functional independence of individuals with reduced abilities to perform basic human functions.

APPLICATION AND/OR ADVANTAGES

1. Dependence on electrical power: The mechanism of present invention is completely a mechanical design that operates passively without the need for electrical actuators, electronic sensing, or control mechanisms.

2. Customizability: The present invention allows for adjustable torque as well as motion characteristics while also allowing for a range of in-situ adjustment to different users in the same configured settings. People have unique ways of sitting down and standing up, by regarding which, this invention provides a near seamless assistive experience.

3. Retrofit ability: The present invention allows for integration with market available seating furniture with a minimal footprint. This implies that the invention carries the best of both ends – seamless integration with the seating experience as if it were designed as inbuilt, as well as a wide range of furniture options. People have been making chairs for a long time, we hold the expertise in enhancing their experience with an add-on. The present invention’s inherent retrofit ability allows us to extend this expertise to any and all chairs/sofas.

4. STS Motion Trajectory: The present invention not only accounts for the natural profiles traced by the users’ center of masses, but distinctly allows for adjustment of the same for different users – while being integrated seamlessly into existing furniture. This is achieved either as a preset adjustment to the available dimensional options during assembly, or as DIY adjustments on the user’s end. Further, in the same configuration, the relative lack of rigidity given the 2 degree of freedom nature of the mechanism allows for in situ adjustment within a range.

5. Mechanical Classification of intent: The mechanical setup allows for kineto-elastically linked but distinct degrees of freedom, which further allows for an extent of ‘smartness’ implemented in the device – mechanically itself. The resultant behavior of the mechanism allows for intent classification. While sitting, there is no force exerted on the user. Once stood up completely, there is no force exerted on the user. However, during this activity of going from the former to the latter, forces are applied in accordance with the requirements of STS dynamics, which are available in literature and can be adjusted according to the user’s inputs. When the activity starts, need not to be activated explicitly, i.e., with a switch or with a knob (as is the case with the state of the art). In this invention, the user needs only to intend to stand up (or sit down) and initiate the same activity naturally (in their body) and the mechanism responds by assisting them along the configured trajectory – reducing the effort all along (measurable as MCR – metabolic cost reduction).

6. The mechanism is capable of mechanically programmable smartness to gauge the user’s intent, as estimated from characteristic dynamics of STS (sit to stand/stand to sit) motion, this ability of recognition of intent, whereby the dynamics of a user’s behavior when attempting to sit down or stand up and classifying it distinctly from that of their otherwise arbitrary movements makes it responsive in nature.

7. The mechanism design is customizable to the specific user’s requirements by configuring adjustable mechanical dimensions, but also adjusts to different users’ requirements (while in the same configured setting) within a range of torque profiles and trajectories.

8. The mechanism is customizable to adjust for user profiles in terms of both the torque response and path (end-effector trajectory), can be achieved both individually as well as combined, contributing to a more precise way of assisting the user in all phases of sit-to-stand and stand-to-seat maneuvers.

9. In mechanism of the present invention, the cams are replaceable to account for the specific torque profile requirement of the user whereby allowing for personalization with tunable torque profiles.

10. The mechanism allows for integration with market-available seating furniture with a minimal footprint both in private (commode and public settings (chair/sofa).

11. The mechanism is characterized by its flexibility in terms of material choices for the components, the materials encompass not only metals and non-metallic (plastic) substances but also their potential combinations.

12. The use of power-assisted mechanisms with the aid of electrical actuators, electronic sensing, or control mechanisms are obvious extensions and covered here and elsewhere.

,CLAIMS:1. A customizable and responsive sit-to-stand (STS) and back-to-sit (BTS) assistance device comprising:
i) a sequence of two-degree of freedom (2-DOF) system;
ii) a compliant hinge (2);
iii) a pneumatic strut (3);
iv) a pair of cams mounted on top of the compliant hinge (2) as a holding means which allows a provision for tunable torque profiles; and
v) a means for holding the device rigidly at the ends, even with minimal footprint;
wherein, the unique mechanism of compliant hinge (2) and gas spring of 2-DOF system supports all the four phases of sit-to-stand or back-to-sit maneuvers, and during all body-extension and stabilization phases.

2. The device as claimed in claim 1, wherein sequence of two-degree of freedom (2-DOF) system is enabled by passive mechanical actuators.

3. The device as claimed in claim 1, wherein 2-DOF system allows responsiveness and is provided with a typical trajectory linkage mounted as floating atop of compliant hinge.

4. The device as claimed in claim 1, wherein the compliant hinge (2) of 2-DOF system having open-circular cross-section shells, bend and twist to provide customized torque-angle characteristics with negative stiffness and bi-stability features, thereby the device is customizable within a range of torque profiles and trajectories.

5. The device as claimed in claim 1, wherein the 2-DOF system is provided with a typical trajectory linkage mounted as floating atop of compliant hinge that is further separated into a four-bar linkage and a slider crank mechanism, with the crank and slider segments of the latter extended from the coupler and rocker segments of the former respectively, and is responsible for the characteristic trajectory with in-situ adjustment.

6. The device as claimed in claim 1, wherein the compliant hinge is an optimized weight and assembly with open-circular cross-section shells which allows tunable torque profiles with replacement of a cam components.

7. The device as claimed in claim 1, wherein a pneumatic strut (gas spring) (3) is a passive provision for segment adjustments which permits the gas spring linage to hinge at an appropriate distance from the common rotation joint to offer different torque profiles serve same geometric configuration for multiple users.

8. The device as claimed in claim 7, wherein the pneumatic strut is independently connected to four bars between the compliant hinge and rocker.

9. The device as claimed in claim 1, wherein the device is mechanically programmable for recording altered responsiveness, where the extent and nature responsiveness of the device is carried out by changing the cam profile and the dimensions of the gas spring mounting location based on recognition of user’s intent, or behavior or movements or attempt, by estimating characteristic dynamics of sit to stand or back to sit motion.

10. The device as claimed in claim 1, wherein the pair of cams are replaceable to account specific torque profile requirement of the user.

11. The device as claimed in claim 1, wherein the device is operated passively without any supportive electrical actuators, electronic sensing, or control mechanisms.

12. The device as claimed in claim 1, wherein the device further comprising an adjustable frame (1).

13. The device as claimed in claim 1, wherein the device can be made of metals and non-metallic (plastic) materials or combinations thereof.

14. The device as claimed in claim 2, wherein the mechanical actuators of device are compliant hinge (2) and a pneumatic strut (gas spring) (3), which can be optionally replaced with power-assisted mechanisms such as supportive electrical or electronic actuators, or control mechanisms.

15. The device as claimed in claim 1, wherein the device can be retrofitted with available seating furniture with a minimal footprint, both in private (commode) and public seating (chair/sofa).