Claims:We Claim:
1. A gearless spherical robot comprising:
a spherical hull having at least two hemispheres;
a yoke plate connected to the spherical hull;
at least two pendulums positioned on either side of a centre of the yoke plate, wherein each pendulum from the at least two pendulums comprises a square shaped upper section, a rectangular shaped middle section and a curve shaped lower section; and
a plurality of mounting brackets for connecting a plurality of electronic components of an electronic unit to the yoke plate, wherein each mounting bracket comprises at least a top portion and a bottom portion and encapsulates at least one electronic component of the electronic unit.

2. The gearless spherical robot as claimed in claim 1, wherein the plurality of electronic components of the electronic unit comprises:
at least two first servo motors mounted on the yoke plate for actuating rolling motion;
a programmable microcontroller mounted on the yoke plate to provide control signals for motion based actuations, wherein the programmable microcontroller is designed to transmit and receive data from a plurality of sensors connected to the electronic unit;
at least one navigational sensor mounted on the yoke plate for measuring position of the gearless spherical robot;
a Lithium Polymer battery mounted on the yoke plate for providing a power supply to the electronic unit;
a voltage regulator connected to the Lithium Polymer battery for providing constant power supply to the electronic unit; and
a radio frequency transceiver mounted on the yoke plate, configured to transmit and receive data from a computing device through a wireless communication system.

3. The gearless spherical robot as claimed in claim 2, the radio frequency transceiver is a Xbee wireless transceiver.

4. The gearless spherical robot as claimed in claim 2, the navigational sensor comprises at least one Global Positioning system (GPS) module.

5. The gearless spherical robot as claimed in claim 1, further comprises at least two second digital servo motors coupled with the at least two pendulums to provide steering motion.

6. The gearless spherical robot as claimed in claim 5, wherein each servo motor from the at least two second servo motor, independently controls the steering motion for each of the pendulums from the at least two pendulums.

, Description:TECHNICAL FIELD
[0001] The present invention relates to a gearless spherical robot and more particularly relates to a novel design with a yoke plate and pendulum assembly without gears. This novel design with the special shape of pendulums helps in reducing size of the robot and in rugged design.

BACKGROUND
[0002] Spherical robots have been developed recent years. Currently wheeled and legged robots are used for space explorations, security and surveillance tasks. Spherical robots have several advantages over conventional wheeled and legged robots including inner component protection, good dynamic stability, low rolling resistance and the ability to move in any direction. Spherical robots work in any harsh environments like snow, mud and even in water because of their outer sealed surface. These robots can be used for planetary surface explorations and security tasks. But the main difficulty arises upon modeling, stabilization and path following of the spherical robots.

[0003] Spherical robots can be divided into two major groups: shell drive type and pendulum type spherical robots. Shell drive type spherical robots comprise a drive mechanism that is supported by and moveable along the shell inner surface. Pendulum type spherical robots comprise a main axle connected diametrically to the shell and supporting a drive mechanism arranged to drive a ballast pendulum for rotation around the main axle. Shell drive type spherical robots are particularly sensitive to shocks. In harsh terrain or by force applied from the outside, the driving mechanism can be easily damaged. Pendulum type spherical robots are therefore considered more robust in structure especially when the pendulum is short and thus high center of mass is high.

[0004] Several methods have been developed for common designs of spherical robots. These designs include single wheel, internal weight, car and single pendulum as actuators, but these have many disadvantages. There are problems with stable steering and balancing control for the single wheel type spherical robots. In the car type spherical robots, difficulty arises in controlling the robot in case of non-contact between the inside of the outer shell and car wheel. In this car type design, achieving the desired maneuverability after a collision is difficult and hence it doesn’t guarantee recapitulate after collision.

[0005] Further, some other spherical robots are developed with one or two pendulums with a driving mechanism. Single pendulum designs require a geared assembly for providing actuation through the motor. But, the geared assembly prohibits its usage in rough environments. Moreover, single pendulum type lacks in omni-directional movement. In some other development methods, a counterweight with the driving mechanism acts as a pendulum assembly in a ball robot, but the counterweight assembly cannot take an entire 360 degrees of rotation. Further, fast steering is difficult in internal weight type spherical robots.

SUMMARY
[0006] In an aspect of the present invention, a gearless spherical robot comprising a spherical hull having at least two hemispheres; a yoke plate connected to the spherical hull; at least two pendulums positioned on either side of a centre of the yoke plate. Each pendulum comprises at least a square shaped upper section, a rectangular shaped middle section and curve shaped lower section. Further, the gearless spherical robot comprising a plurality of mounting brackets for connecting a plurality of electronic components of an electronic unit to the yoke plate. Each mounting bracket comprises at least a top portion and a bottom portion and encapsulates at least one electronic component of the electronic unit.

BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The detailed description is described with reference to the accompanying figures.

[0008] Figure 1, illustrates a gearless spherical robot according to the exemplary embodiment of the present invention.

[0009] Figure 2, illustrates a novel pendulum design according to the exemplary embodiment of the present invention.

[0010] Figure 3, illustrates the gearless spherical robot with an internal assembly consisting of an electronic unit according to the exemplary embodiment of the present invention.

[0011] Figure 4, illustrates a block diagram of electronic components of an electronic unit connected to the yoke plate.

[0012] Figure 5, illustrates a flow chart describing the procedure of executing input commands through the motors for motion control.

[0013] Figure 6, illustrates a top view of the gearless spherical robot with a wheel according to a further embodiment of the present invention.

DETAILED DESCRIPTION
[0014] In an exemplary embodiment of the present invention, a gearless spherical robot is disclosed. Referring to figure 1, there is shown the novel gearless spherical robot 100 comprising a spherical hull 101, a yoke plate 102, two pendulums 103 and a plurality of mounting brackets 104 for encapsulating various electronic components. Further, the gearless spherical robot comprises internal assembly with an electronic unit consisting of a plurality of electronic components connected to the yoke plate.

[0015] The yoke plate and pendulum based design is selected to support recovery after any collision. The novel shape of the pendulums is selected and the selected shape increases the ratio of moment of inertia of pendulum and the entire assembly. The novel shape of the pendulums further supports maneuverability of the robot design using pendulum motion.

[0016] The spherical hull comprising at least two hemispheres made up of an acrylic material. The hemispheres may be fabricated with the help of blow moulding process. It may be appreciated that dimensions of the hemispheres may be varied depending on the design requirements. In one implementation, the hemispheres may be formed with the dimensions of 190 mm inner diameter and 3 mm – 4 mm thickness. All the electronic and mechanical components are placed inside the spherical hull such that each and every component of the gearless spherical robot is moving while it is in operation. This design ultimately minimizes the size of entire robotic assembly, thus miniaturization may be possible with the described novel gearless spherical robot. A circular disc shaped yoke plate may be connected to the spherical hull. All mechanical and electronic components are directly or indirectly connected to the yoke plate. The yoke plate may be connected to the spherical hull with the help of the shaft of servo motors. The yoke plate may be fabricated on a 5 mm thick acrylic sheet using a laser cutting process.

[0017] In an exemplary embodiment of the present invention, the gearless spherical robot comprises of two pendulums made of mild steel material. The two pendulums may be positioned on either side of a centre of the yoke plate. The two pendulum assembly is primarily designed to avoid gears in rough environments and also to maintain the symmetry of the design. These pendulums may be driven by two continuous servo motors rotating about the horizontal axis and vertical axis. Such an assembly generates eccentric moment helps in left or right steering motion of the gearless spherical robot. The pendulums may be used for shifting the entire mass of the gearless spherical robot. Referring to figure 2, there is shown a novel pendulum design according to the exemplary embodiment of the invention. The novel pendulum has at least three sections comprising an upper section 201, a middle section 202 and a lower section 203 and weighs at least 193 grams. The upper section 201 may be formed in a square shape, the middle section 202 may be formed in a rectangular shape and the lower section 203 may be formed in a curved shape. Such shape of the pendulums is selected to increase the ratio of moment of inertia of pendulum and the entire assembly to allow movement in the direction of pendulum rotation axis.

[0018] The plurality of mounting brackets may be used to connect various mechanical and electronic components to the yoke plate. Each bracket consists of a top portion and a bottom portion for encapsulating the desired component. The brackets may be fabricated using Makerbot replicator on an acrylonitrile butadiene styrene (ABS) plastic material. The Makerbot replicator is a full featured desktop printer with a resolution of 0.1 mm. The acrylonitrile butadiene styrene (ABS) plastic material may be used as a filament having width of 1.75 mm/1.8 mm. In one embodiment of the present invention, three types of mounting brackets may be used for housing servo motors, digital servo motors and for batteries. It may be appreciated that the size and shape of mounting bracket may be varied depending on the size and shape of the housing component.

[0019] Referring to figure 3, there is shown the gearless spherical robot 300 with an internal assembly consisting of an electronic unit housed inside the two hemispheres 301a and 301b. As described in the above, the electronic unit comprises a plurality of electronic components. The plurality of electronic components may comprise a battery (not shown), two digital servomotors connected to pendulums 302, a voltage regulator (not shown), two yoke servo motors for rolling motion 303, a programmable microcontroller 304, a navigational sensor (not shown) and a radio frequency transceiver 305.

[0020] Referring to figure 4, there is shown a block diagram of electronic components of the electronic unit 400. The battery unit 401 shown may be lithium polymer (LiPo) battery and providing an output voltage of 7.4 V. The battery unit 401 may be connected to a charger 402 through a charging port (not shown) to receive its power supply. In one implementation of the present invention, the battery unit 401 may comprise at least two lithium polymer battery units with the capacity of 1300 mAh. An on/off switch 403 may be connected to the battery unit for providing the power supply to the remaining electronic components of the electronic unit. With the on/off switch and charging port, the gearless spherical robot provides an ease of operation without disconnecting from the spherical shell.

[0021] Two continuous rotation digital servomotors 405 may be mounted on the yoke plate and connected with each pendulum for actuating left and right steering motion. These servomotors may be operated in open loop control and may provide a precise position of the pendulum angle in the presence of the load. Each servomotor independently controls the steering motion for each of the pendulums from the at least two pendulums. These servomotors 405 may be connected to the on/off switch 403 to receive 7.4 V power supply from the battery unit. Two digital servomotors can rotate about the horizontal axis and vertical axis and generate an eccentric motion to roll linearly or to steer left/right. In one implementation of the present invention, Dynamixel Ax-12 type servomotors may be used for actuating steering motions. According to one implementation of the present invention, Dynamixel Ax-12 type servomotors may be used for pendulum motion. Data pins of these digital servomotors may be connected to a tri-state buffer of the electronic unit.

[0022] The voltage regulator 406 of the electronic unit may be connected to the battery unit through the switch for providing a regulated power supply to the servomotors and to the remaining electronic components. The voltage regulator 406 outputs a constant voltage of 5 V from the 7.4 V battery unit. Further, the programmable microcontroller may be mounted on the yoke plate for controlling the robotic motions. The programmable microcontroller 407 is connected to two servomotors, two digital servo motors and to a radio frequency transceiver. Such connections enable the programmable microcontroller to control all the actuations, transmitting/ receiving of data from/to a plurality of sensors connected to the electronic unit. The programmable microcontroller as an autonomous controller may be used in an autonomous control of the gearless spherical robot. In one implementation of the present invention, the programmable microcontroller 407 may be an Arduino Uno Micro-controller. The Arduino Uno Micro-controller may be chosen because of its small size for the described design. This controller may comprise an embedded Atmega32 microprocessor.

[0023] Two servo motors 408 may be mounted on the yoke plate (not shown) and connected to the programmable microcontroller 407 for actuating forward and backward rolling motion for the gearless spherical robot. These servo motors are generally called as yoke servomotors. The servo motors are chosen in the novel design because of its high torque and relatively low mass as compared to DC stepper motors providing the same torque. In one implementation of the present invention, a HS - 225MG type continuous servo motor from Hitec may be used as yoke servomotors. Complete 360 degrees rotation on these servo motors may be achieved by shorting the internal potentiometer of the servo motors.

[0024] Further, the radio frequency transceiver 409 may be mounted on the yoke plate for providing wireless communications and data transfer between the electronic components. The radio frequency transceiver 409 of the gearless spherical robot may be configured to transmit and receive data from a computing device through a wireless communication system. The computing device may be any suitable portable device not only limited to a computer, mobile device, tablet, palmtop, laptop, Smartphone. The wireless communication system may be any suitable wireless communication methods not only limited to Wi-Fi, WiMAX, ZigBee, mobile communications or any suitable short range communication methods such as Bluetooth. In one implementation, the radio frequency transceiver may be a Xbee transceiver. The Xbee transceiver may comprise transmitter and receiver pins connected to the software serial pins of the Arduino Uno Micro-controller. Further, the navigational sensor 410 may also be connected to the serial pins of the Arduino Uno Micro-controller. The navigational sensor 410 may be a global positioning system (GPS) sensor. The Arduino may be serially receiving longitude and latitude data from the GPS sensor. The electronic unit further may comprise a tri-state buffer 411 connected to the Arduino Uno Micro-controller 407 and the voltage regulator 406. In the present embodiment of the invention, an integrated chip (IC) of tri-state buffer may be used. The tri-state buffer IC receives the power supply from the voltage regulator.

[0025] In one embodiment of the present invention, the gearless spherical robot can be controlled either by a remote control or an autonomous controller. During control mode, the gearless spherical robot follows the input commands such as move straight, move left and move right. Referring to figure 5, there is shown a flow chart 500 describing the procedure of executing input commands through the motors for motion control. If the command is to move straight, the autonomous controller or a user (through a remote control device) selects a forward rolling velocity (Vs) at step 501. Similarly a left turning velocity (Vl) and a right turning velocity (Vr) may be selected for move left at step 502 and move right commands at step 503 respectively. The appropriate Pulse width Modulation (PWM) signal for the selected command may be provided to the yoke servomotors through the programmable microcontroller. At step 504, a look-up table may be prepared by calibrating the yoke servomotors and measuring the rolling velocity for a given calibrated duty cycle of PWM signal. The PWM voltage corresponding to forward rolling velocity (PWMs) may be obtained using the look-up table. Similarly, PWM voltages for left rolling velocity (PWMl) and for right rolling velocity (PWMr) may also be obtained using the look-up table. Vmax shown is the maximum possible velocity of the gearless spherical robot and PWMmax is the corresponding PWM voltage. Further, the obtained PWM voltages may be provided to the yoke servomotors for the desired commands through the PWM pins of the programmable microcontroller at step 505.

[0026] Turning motion with the desired angle may be achieved by actuating the two pendulums connected to yoke plate to an angle. Higher pendulum angle provides more curvature path of the turning direction. If the turning direction is left, commands provide a left turning with a turning angle Ol at step 506. Similarly, if the turning direction is right the commands provide a right turning with a turning angle Or at step 507. The turning direction mainly depends on the direction of rotation of the two pendulums. Hence, a system model may be developed to obtain a relationship between the turning velocity and pendulum angle. A look-up table for providing a relation between a turning angle and pendulum angle may be prepared using a graphical method at step 508. Using the relationship between pendulum angle and the PWM voltage of digital servomotors connected to the pendulums, the duty cycle of PWM for digital servomotors for the corresponding pendulum angle may also be computed at step 509. Further, the obtained PWM voltages may be provided to the digital servomotors connected to the pendulums through the PWM pins of the programmable microcontroller at step 510.

[0027] Referring to figure 6, there is shown a top view of the gearless spherical robot 600 with a wheel 601 according to a further embodiment of the present invention. The wheel may be fitted on the outside body of the spherical hull. This wheel design may facilitate a single point of contact with the environment. Such wheel design may be used in applications in cleaning and searching tasks.

[0028] The gearless spherical robot according to the present invention can be used in autonomous, semi-autonomous and remote –controlled modes. The autonomous mode is possible by obtaining location feedback from the GPS sensors interfaced with the programmable microcontroller board. Only one physical point of contact with the environment supports its use in rough environments. The charging port and its wiring are placed inside the spherical hull such that the battery unit can be charged without removing them from the gearless spherical robot. The entire electronic and mechanical assembly is covered inside the spherical hull facilitating protection against dust, humidity, mud and other environmental factors. Further, the use of low end embedded microprocessor avoids the overheating.

[0029] Although the invention has been disclosed in the context of certain aspects and embodiments, it will be understood by those skilled in the art that the present invention extends beyond the specific embodiments to alternative embodiments and/or uses of the invention and obvious implementations and equivalents thereof. Thus, it is intended that the scope of the present invention disclosed herein should not be limited by the disclosed aspects and embodiments above.