GB2554876A

GB2554876A - Haptic device

Info

Publication number: GB2554876A
Application number: GB1617167.0A
Authority: GB
Inventors: Barrow Alastair; Alan Smith Thomas
Original assignee: Generic Robotics
Current assignee: Generic Robotics
Priority date: 2016-10-12
Filing date: 2016-10-12
Publication date: 2018-04-18
Anticipated expiration: 2036-10-12
Also published as: GB201617167D0; GB2554876B

Abstract

A robot arm for use in a haptic device comprises actuators A1-A4 mounted in fixed relation which drive an arrangement of two robot arms 126, 130 and 146, 150 that, in turn, support a tool 136. Joints 124, 144 couple the movement of the robot arms 126, 130 and 146, 150 to the actuators A1-A4 in different rotary directions to allow movement of the tool throughout a three dimensional workspace. By arranging the actuators "off board", a light, responsive haptic device is provided. The device preferably comprises a removable tool with a connector (402, 404 fig. 4) and interchangeable arms (146, 150 fig. 7), preferably facilitated by magnetic couplings (414, 416 fig. 4). Further preferably the couplings are provided with electrical connections (518, 520 fig. 5) to allow sensing and other signals to be conveyed through the robot arms, such as the output of force sensors or strain gauges (802, 804 fig. 8) mounted to the arms of the robot.

Description

(54) Title of the Invention: Haptic device

Abstract Title: A robot arm for use in a haptic device (57) A robot arm for use in a haptic device comprises actuators A1-A4 mounted in fixed relation which drive an arrangement of two robot arms 126, 130 and 146, 150 that, in turn, support a tool 136. Joints 124, 144 couple the movement of the robot arms 126, 130 and 146, 150 to the actuators A1-A4 in different rotary directions to allow movement of the tool throughout a three dimensional workspace. By arranging the actuators off board, a light, responsive haptic device is provided. The device preferably comprises a removable tool with a connector (402, 404 fig. 4) and interchangeable arms (146, 150 fig. 7), preferably facilitated by magnetic couplings (414, 416 fig. 4). Further preferably the couplings are provided with electrical connections (518, 520 fig. 5) to allow sensing and other signals to be conveyed through the robot arms, such as the output of force sensors or strain gauges (802, 804 fig.

8) mounted to the arms of the robot.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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FIG.

FIG. 7

HAPTIC DEVICE

The present invention relates to a haptic device, in particular a haptic device comprising a novel arrangement of robot arms. The invention further relates to a connector for connecting end-effectors to a haptic device, to an arrangement of robot arms that is user-modifiable, and to a force-sensing arrangement for use in a haptic device.

Haptic devices are known, for example, to train personnel in delicate mechanical tasks such as surgical procedures or dentistry. Haptic devices typically comprise an arrangement of robot arms connected to a user-device (end effector or tool) and to a number of motors/actuators so that movement of the user-device in free space is converted to rotations of the axles of the motors. The motors are further provided with position sensors and a processor converts the position of the userdevice (inferred from the sensor outputs) into drive signals for the motors. A user holding the user device can then be given the perception of different behaviours in response to applied force or movement to simulate a particular environment.

One difficulty with some arrangements of robot arms used in haptic applications is that motors are mounted on the joints of the robot arms. This makes the whole arrangement heavier and more unwieldy as well as necessitating larger motors at the base of the robot arms to provide extra torque to move the joint-mounted motors.

According to a first aspect of the present invention, there is provided a haptic device including three actuators secured in fixed relation and having a first elbowed arm and a second elbowed arm, each arm connected, in use, together at a distal point, the first arm being connected to a first actuator via a joint that conveys rotation between the arm and the actuator in one rotary direction, the second arm connected to a second actuator and a third actuator via a joint that conveys rotation between the arm and the second actuator in one rotary direction and that conveys rotation between the arm and the third actuator in another rotary direction.

By locating the actuators/motors together away from the user-engaging end of the device, the heavy actuators/motors are not borne on the robot arms with which the user engages, making the whole arrangement lighter and more responsive.

In a preferred embodiment, a fourth actuator is provided that additionally couples to the first robot arm to permit rotation in a different dimension to the first actuator.

Another difficulty is that of connecting tools or end-effectors to the distal ends of the robot arm or arms. Firm mechanical connections (and often electrical connections) need to be made between the robot arm and the tool so as to ensure that the user receives accurate feedback. Using screws, for example, takes time and has a risk that the tool will not be connected correctly.

According to a second aspect of the present invention there is provided a robot arm, for use in a haptic device, having a coupling for a tool, wherein the coupling for a tool comprises a magnetic coupling.

By providing a magnetic coupling, the tool or tools can be attached quickly, firmly and accurately. The coupling may comprise permanent magnet to permanent magnet, permanent magnet to magnetic material, electromagnet to permanent magnet or electromagnet to magnetic material.

In a preferred embodiment the coupling in the robot arm is also provided with one or more electrical connectors. Often the tool to be attached has a button or other electrical transducer to sense user input. This feature allows electrical signals to be transmitted to the controlling circuity at the other end of the robot arm(s). The particular tool which is attached may also be detected automatically by connecting it, via conductors in the robot arms, to the controlling circuitry.

In addition to coupling of tools or end-effectors, the magnetic couplings may be used to vary the performance of the device. Haptic devices are typically set up using a particular arrangement of robot arms which necessitates a trade-off between range of motion and applicable forces. Longer robot arms allow movement of the end-effector over a larger space but, because the motors provide a fixed amount of torque, the force applicable at the end-effector is reduced. The converse is true of shorter robot arms.

According to a third aspect of the present invention there is provided a robot arm, for use in a haptic device, having at least one interchangeable arm or member.

By allowing a user to swap the arrangement of robot arms, the best trade off between range of motion, shape of accessible workspace and applicable force for a particular application may be selected. The length of the arm is preferably read automatically, as for the interchangeable tools.

While any suitable couplings could be provided at the ends of the interchangeable arm, preferably, a coupling at each end of the interchangeable arm comprises a magnetic coupling.

Force sensing is a part of haptic devices, particularly so-called admittance type haptic devices but force sensors are typically bulky and expensive which impacts the usability of a haptic device.

According to a fourth aspect of the present invention, there is provided a robot arm for use in a haptic device, which robot arm includes at least one force sensor.

Preferably a pair of force sensors are provided, arranged to detect forces in different dimensions. Typically, the sensors will be arranged orthogonally around the arm or member but this is not essential.

In a preferred embodiment, the force sensor comprises a strain gauge.

By integrating the force sensors into the arms of the haptic device a significant saving in size and weight of the arrangement, particularly at the distal end of the robot arms where it is particularly critical. The force sensor is suitable for use with both admittance style devices and hybrid admittance/impedance haptic devices.

Brief description of the Figures

Figure 1 shows a three dimensional view of haptic device comprising a pantograph in accordance with a first embodiment of the present invention,

Figure 2 shows a three dimensional view of a part of the pantograph of Figure 1,

Figure 3 is similar to Figure 2, from a different angle,

Figures 4 and 5 show a connector, for use with a haptic device, in accordance with a second embodiment of the present invention,

Figures 6 and 7 show an arrangement of detachable robot arms provided with magnetic couplings in accordance with a third embodiment of the invention, and

Figure 8 shows an integrated force sensor, for use with a haptic device, in accordance with a fourth embodiment of the present invention.

Detailed description of the preferred Embodiments

Figures 1 to 3 show views of haptic device comprising a pantograph in accordance with a first embodiment of the present invention. One of the difficulties with known arrangements of robot arms used in haptic applications is that motors are mounted on the joints of the robot arms. This makes the whole arrangement heavier and more unwieldy as well as necessitating larger motors at the base of the robot arms to carry the extra weight. By contrast, the present embodiment moves the (heavy) motors “off-board” without sacrificing the range of movement or user experience of the haptic feedback.

Figure 1 shows a perspective view of a pantograph 100 including a tool or end-effector (shown here as a handle 136) connected via two single-jointed arms to a further arrangement of joints and four actuators/ motors. The tool is able to move throughout three-dimensional space . Due to the arrangement of the joints and arms attached to the motors, any movement of the tool will be translated into a rotational motion in one or more of the motors. Sensors (not shown) determine the position of the motors in known manner. By driving the motors appropriately, haptic feedback can be provided to a user holding the tool.

Four actuators Al, A2, A3, A4 are mounted in a fixed arrangement with Al and A2 mounted in the Y direction and A3, A4 mounted in the Z direction. An axle 120 of actuator A2 is connected to a member 122 and via some further members (to be described with reference to Figure 2) to a joint 124. The joint 124 is connected to an arm 126 and is arranged to convey rotation of that arm in the X-Y plane to the axle of the actuator A4. The joint is further arranged to convey rotation of the arm 126 in the plane X-Z to the axle 120 of actuator A2. The arm 126 is connected via a joint 128 to a further arm 130, the joint allowing free rotation around its axis but no appreciable movement in any other dimension. The arm 130 is connected to a joint 132 which in turn is connected to a joint 134 that is coupled to the tool 136. The arrangement described thus far comprises one robot arm.

A further robot arm and actuator arrangement is also provided which is effectively a mirror image of the first one. It comprises an actuator Al coupled via members to a joint 144 which is also connected to actuator A3. This joint is connected in turn to an arm 146, joint 148, arm 150, joint 152, joint 134 and tool 136. The joint 144 operates similarly to the joint 124 in that motion of the tool in the Z direction is translated into rotation of the axle of actuator Al and that rotation of the arm 146 in the X-Y plane is converted into rotation of the actuator A3.

Fore and aft motion of the tool (in the direction of the X axis in the figure) will open and close the elbows of the two arms which in turn will rotate the axles of the motors A3, A4 connected to the ends of those arms. Left-right movement (in the Y direction) will open the elbow of one of the arms while closing the elbow of the other, again producing rotary motion at the axles of the motors A3, A4. Up and down movement of the tool (in the Z direction) will rotate the axles of the motors Al, A2 while a twisting motion of the tool around the X axis will drive the axles of the motors Al, A2 in opposite directions.

Although not shown for clarity, the four motors are mounted to a frame which bears their weight. Using this arrangement, the forces generated by the motors are available to provide forces to the user, without torque being wasted just to support some other motors.

Figure 2 shows a portion of the arrangement shown in Figure 1 from approximately the angle shown by the arrow 200 in Figure 1. The shaft 240 of Actuator Al is connected to a short, solid member 242 which extends into member 220. Member 220 has a pair of rotational joints with two further members 222 and 224. These members in turn are connected via rotating joints to member 218, forming a parallelogram with member 220. When the axle of the actuator Al rotates, members 218 and 220 will remain parallel to each other, as will members 222 and 224. The purpose of the parallelogram is to convey rotary movement of the joint 144 (Figure 1) in the plane X-Z into rotary movement of the axle 240 of the actuator Al. In more detail, the joint 144 comprises a coupling 210 to arm 146, a coupling 212 to actuator A3 (only partially shown) and a coupling 214, 216 to the parallelogram. As stated above, the purpose of these members and joints is to convey motion of the arm 146 around the joint 144 into rotation of the axles of the actuators Al and A3.

To illustrate the functioning of the joint 144 in more detail, Figure 3 shows a closer view of the joint from approximately the direction of the arrow 300 shown in Figure 2. In particular, the coupling 210 is provided with a rotating axis 302 that permits rotation of arm 146 in the X-Z plane while coupling rotation of the arm 146 in the X-Y plane to actuator A3. A similar rotating axis is provided orthogonal to axis 302 to allow free movement of arm 146 in the X-Y plane while coupling rotation thereof in the X-Z plane, via the parallelogram, to actuator Al (partially shown). The joint 124 of the first robot arm operates in an analogous manner.

Driving of the motors in accordance with the sensed position of the tool and the desired behaviour of the apparatus will be known to those having ordinary skill in the art. There are effectively two steps:

the calculations to map from joint-space to world space and back to get position of the end point and correctly calculate the appropriate joint torques to create a desired resulting Cartesian force.

The tool 136 is connected to the pair of robot arms via a coupling 134 to allow different tools to be fitted as described further with reference to Figures 4 and 5. The joints of the pantograph are provided with couplings 132, 152, 210 as described further below to allow different length arms to be fitted for different applications.

In a variant, the two actuators A3 and A4 are mounted above one another (i.e. in line in the Z direction) with one having its coupling to the robot arm underneath it and the other having its coupling to the other robot arm above it. Thus, in plan view, the robot arms arrangement is diamond-shaped.

While the embodiment described is provided with four actuators Al - A4, it should be noted that one of actuators Al or A2 may be omitted. In this case, the coupling of the robot arms to the tool must be rigid (in other words, no torque can be applied or measured at the tool). Motion of the tool in the Z direction will then rotate the axle of only one actuator but the tool can still move throughout the 3 dimensional workspace with haptic feedback being applied.

Figures 4 and 5 illustrate the second embodiment of the present invention, which includes a connector for the end-effector or tool which the user of a haptic device holds. This connector may be used both with the haptic arrangement of the first embodiment and with other haptic devices, such as training devices.

Electrical connections are provided so that the tool can be provided with further sensors, switches or active devices. For example, the tool could be provided with a sensor to check whether a user is actually holding the tool. A switch may be provided to actually activate the tool - for example a tool simulating a dental drill will usually be provided with a three way switch for forwards/off/reverse operation. The controlling processor will need to be provided with the position of that switch. Alternatively or in addition, the tool may comprise a motor to provide the user with a sensation of vibration and/or torque when the tool is “on” and engaging something in the virtual environment. While the electrical connections provide a convenient connection for the outputs of sensors and the drive signals for a motor, they may be absent, i.e. the connector may be purely mechanical in some applications.

Figure 4 shows a perspective view of a male 402 and female 404 connector according to the second embodiment. The two parts are aligned for connection but separated slightly to permit a better view of the internal components of the connector. The male mechanical connector 402 comprises a female electrical connector and vice versa. A series of magnets 414, 416 are provided across the two parts of the connector to hold the male and female parts of the connector firmly together when the parts are engaged. When the parts are engaged, magnetic portions 414, 416 are preferably in contact to provide a stable mechanical connection. The male connector carries a protrusion 406 which engages with a slot 408 in the female connector when they are coupled together. This ensures both the correct mechanical orientation of the two parts while coupled and the correct alignment of the electrical connections.

On the female side, the magnet 416 comprises three ring-shaped magnets arranged axially with four electrical connectors (pins) 418 located within the ring and connected to a cable 412. Similarly, on the male side, three ring-shaped magnets 414 are arranged axially around a female connector which is coupled to a cable 410. Although the female connector is not visible, it will be understood that this will comprise four sockets for accepting the pins 418 when the two parts of the connector are attached.

Figure 5 shows three further views of the connector of Figure 4. In Figure 5(a) we have an elevation of the connector with the female part 404 and the male part 402 slightly separated. Figure 5(b) shows a three-dimensional view to better illustrate the anti-rotation feature provided by the protrusion 406 and the slot 408. Figure 5(c) is a cutaway elevation of the male and female connectors showing that the pins 418 are carried by a small PCB or Male connection board and the corresponding female connectors are carried by a Female connection board 520.

While the male mechanical connector is shown housing the female electrical connector and viceversa, a male mechanical connector could be provided with the male electrical connectors and similarly for the female connectors. The electrical connectors are preferably recessed within the mechanical connector to provide them with protection from damage. As shown, the connectors are preferably provided on small printed circuit boards (PCBs) mounted transversely across the connectors. The wires or cable from each connector can then be routed through the hollow arms of the tool or the Haptic device.

Four connectors are shown in Figures 4 and 5 which is compatible with a digital arrangement having two power lines and a serial bus conveying the data between the sensors and the control circuitry. This is particularly useful for analogue sensors - by performing the analogue-to-digital conversion close to the sensor, the effects of noise are minimised. Other arrangements, including analogue arrangements having different numbers of connectors could alternatively be used.

While a protrusion is provided on the male connector and a slot on the female connector to prevent rotation of the tool relative to the robot arm (and incorrect insertion of the electrical connectors) other known techniques, for example a flat on the circular surface could equally be used.

The bodies of the male and female connectors are provided with a magnetic coupling to enable quick coupling and decoupling of the connector while providing a strong connection when the connectors are fully engaged. Although the magnetic connection provides a very strong connection, since magnetic force drops quickly with distance, this provides both ease of connection and excellent strength.

Various combinations of magnets and magnetic materials can be used. On the tool side of the connector, a permanent magnet or magnetic material may be provided. On the other side a permanent magnet or electromagnet may be provided (in conjunction with either a magnet or magnetic material on the tool side) or a magnetic material may be provided (in conjunction with a permanent magnet on the tool side).

Figures 6 and 7 show the robot arm arrangement previously described using the principle of the second embodiment to extend to the design of the kinematic arrangement itself. The connectors between the joints and the arms of the robots use the magnetic principle as illustrated above. In Figure 6, the robot arm comprising arms 146, 150 and joint 148 is shown disconnected from the connectors 152 and 210. A different robot arm may then be substituted for a different purpose. For example, a shorter arm will provide more force feedback but a smaller workspace while a longer arm will provide the reverse. The control circuitry will, of course, have to be aware of the particular kinematic arrangement that is connected. This may be done by the user typing the information or selecting options from a user interface. Preferably, however the length and other characteristics of the arms and joints in the arrangement are conveyed to the control circuitry using the connectors are discussed above. Colour-coding may be used to ensure that the correct arms are used for a particular application.

Figure 7 shows a similar view to Figure 6 but without two of the actuators and one of the robot arms so that the disconnection of arm 146 from coupling 210 can be better appreciated.

Thus far in the described embodiments, the sensing of position is carried out by measuring the position of the motors and inferring the position of the end-effector from the motor positions. This is referred to as an impedance style control scheme. In other words, the motion input caused by the user is measured and mapped to a position in a virtual environment. The control algorithm then drives the motors (actuators) to increase the mechanical impedance of the system to match the internal representation of the virtual environment.

In an admittance control scheme, the system uses force sensors to measure forces applied to the system and the control scheme drives the motors/actuators to accelerate the mechanism to alter the mechanical impedance as defined by the internal representation of the virtual environment. The admittance technique requires a multi-axis force sensor having at least as many force axes as there are driven axes to detect the force applied. The drawback is that this sensor is not only typically large and expensive but it must be located at the distal end of the haptic device. This makes the whole arrangement heavier and bulkier which can reduce the usability or range of applications of the device.

Miniature force sensing and multi-axis force sensing are difficult to provide. In particular, one of the challenges in achieving stable control of a system like this is the distance between force sensor, actuator and position sensor introducing errors. In a third embodiment the force sensing function is moved to within the robot arms themselves which provides a space-effective solution. By sensing strain directly within the arms, fewer calculations may be required to determine the position or force applied to the end effector but this will depend upon the arrangement of the robot arms.

Figure 8 shows a close up view of a portion of Figure 1, approximately from the perspective shown by the arrow 800. The key thing to notice are two flats 802, 804 provided on the arm 126, which can conveniently be made by milling. Similar flats are cut into all four arms 126, 130, 146, 150 (Figure 1). The flats are made to provide a mounting surface for strain gauges (not shown) to detect the force applied to the arm. As is known, the strain gauges should be fixed (for example by bonding) securely to the arm in order to accurately measure the bending force applied to the arm. Since the flats 802 and 804 are arranged orthogonally around the arm, forces applied in two dimensions can be measured (some angular spacing is required to allow the controller to determine the bending force applied in two dimensions but the spacing need not be at 90 degrees). The force measurement is conveyed to the controller via the joints, such as those shown in Figures 4 and 5. Preferably the arm contains an analogue to digital converter (not shown) so that the signals are conveyed digitally to the controller.

A significant benefit to this arrangement is that the force sensing and actuation of the corresponding actuator (motor) can be performed on a per-actuator basis i.e. without having to translate the forces into a representation in the virtual environment and then back again. The calculations to allow for for inertia and friction are also simplified.

The robot arm in accordance with this fourth aspect of the invention may be further provided with interchangeable tools in accordance with the second aspect and/or selectable robot arms in accordance with the third aspect.

Although this arrangement is particularly suitable for an admittance control scheme, it is also applicable to hybrid schemes.

Claims

1. A haptic device including three actuators secured in fixed relation and having a first elbowed arm and a second elbowed arm, each arm connected, in use, together at a distal point, the first arm being connected to a first actuator via a joint that conveys rotation between the arm and the actuator in one rotary direction, the second arm connected to a second actuator and a third actuator via a joint that conveys rotation between the arm and the second actuator in one rotary direction and that conveys rotation between the arm and the third actuator in another rotary direction.

2. A haptic device as claimed in claim 1, further comprising a fourth actuator connected to the first arm via the joint which joint further conveys rotation between the arm and the fourth actuator in a further rotary direction to the first actuator.

3. A haptic device as claimed in claim 1 or claim 2, wherein the elbows of the first and second arms are arranged to rotate about axes that are parallel to one another.

4. A haptic device as claimed in any one of the claims 1 to 3, wherein the distal ends of the robot arms are provided with couplings and, in use, are joined by a tool that connects these couplings.

5. A haptic device as claimed in claim 4, wherein the couplings for a tool comprise magnetic couplings.

6. A haptic device as claimed in claim 5, wherein the coupling further comprises an electrical connection.

7. A haptic device as claimed in any one of the claims 1 to 6, further comprising force sensing means which force sensing means includes a force sensor integrated into at least one of the arms of the device.

8. A haptic device as claimed in claim 7, wherein the force sensor includes a strain gauge.

9. A robot arm, for use in a haptic device, having a coupling for a tool, wherein the coupling for a tool comprises a magnetic coupling.

10. A robot arm as claimed in claim 9, wherein the coupling further comprises an electrical connection.

11. A robot arm, for use in a haptic device, having at least one replaceable arm or member.

12. A robot arm as claimed in claim 11, wherein a coupling at each end of the replaceable arm comprises a magnetic coupling.

13. A robot arm as claimed in claim 12, wherein the coupling further comprises an electrical connection.

14. A robot arm as claimed in claim 12 or claim 13, further having a coupling for a tool, wherein the coupling for a tool comprises a magnetic coupling

15. A robot arm for use in a haptic device, which robot arm includes at least one force sensor.

16. A robot arm as claimed in claim 15, wherein a further force sensor is provided, arranged to sense a force in a different dimension.

17. A robot arm as claimed in claim 15 or claim 16, wherein the at least one force sensor is a strain gauge.

Intellectual

Property

Office

Mr Karl Whitfield

27 March 2017

GB1617167.0

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