Method of Controlling Mechanical Impedance of Robot, Control System and Robot

Abstract

A method of controlling a robot, the method including obtaining, by means of a proximity sensor on the robot, a distance value indicative of a distance between an object and the robot; obtaining, by means of a thermal sensor on the robot, a temperature value indicative of a temperature of the object; and controlling the robot to reduce its mechanical impedance if the distance value is smaller than a distance threshold value and the temperature value is higher than a temperature threshold value. A control system for controlling a robot, and a robot including the control system, are also provided.

Claims

1. A method of controlling a robot, the method comprising: obtaining, by a proximity sensor on the robot a distance value indicative of a distance between an object and the robot; obtaining, by a thermal sensor on the robot, a temperature value indicative of a temperature of the object; and controlling the robot to reduce its mechanical impedance if the distance value is smaller than a distance threshold value and the temperature value is higher than a temperature threshold value.

2. The method according to claim 1, wherein the reduction comprises reducing the mechanical impedance more for a smaller distance value than for a larger distance value.

3. The method according to claim 1, further comprising modifying a movement strategy of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

4. The method according to claim 1, further comprising limiting a speed of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

5. The method according to claim 1, further comprising increasing a smoothness of motion of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

6. The method according to claim 1, wherein the robot comprises a manipulator, and wherein the reduction of the mechanical impedance includes reducing a mechanical impedance of the manipulator.

7. The method according to claim 1, wherein the robot is a mobile robot.

8. A control system for controlling a robot, the control system comprising at least one data processing device and at least one memory having a computer program stored thereon, the computer program including a program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform the steps of: obtaining, from a proximity sensor on the robot, a distance value indicative of a distance between an object and the robot; obtaining, from a thermal sensor on the robot a temperature value indicative of a temperature of the object; and controlling the robot to reduce its mechanical impedance if the distance value is smaller than a distance threshold value and the temperature value is higher than a temperature threshold value.

9. The control system according to claim 8, wherein the reduction comprises reducing the mechanical impedance more for a smaller distance value than for a larger distance value.

10. The control system according to claim 8, wherein the computer program comprises program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform the step of: modifying a movement strategy of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

11. The control system according to wherein the computer program comprises program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform the step of: limiting a speed of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

12. The control system according to claim 8, wherein the computer program comprises program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform the step of: increasing a smoothness of motion of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

13. The control system according to claim 8, wherein the reduction of the mechanical impedance includes reducing a mechanical impedance of the manipulator.

14. A robot comprising: a control system including at least one data processing device and at least one memory having a computer program stored thereon, the computer program including a program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform the steps of: obtaining, from a proximity sensor on the robot, a distance value indicative of a distance between an object and the robot; obtaining, from a thermal sensor on the robot, a temperature value indicative of a temperature of the object; and controlling the robot to reduce its mechanical impedance if the distance value is smaller than a distance threshold value and the temperature value is higher than a temperature threshold value, and the proximity sensor provided on the robot, and the thermal sensor, provided on the robot.

15. The robot according to claim 14, wherein the robot is a mobile robot.

16. The method according to claim 2, further comprising modifying a movement strategy of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

17. The method according to claim 2, further comprising limiting a speed of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

18. The method according to claim 2, further comprising increasing a smoothness of motion of the robot if the distance value is smaller than the distance threshold value and the temperature value is higher than the temperature threshold value.

19. The method according to claim 2, wherein the robot comprises a manipulator, and wherein the reduction of the mechanical impedance includes reducing a mechanical impedance of the manipulator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further details, advantages and aspects of the present disclosure will become apparent from the following description taken in conjunction with the drawings, wherein:

[0045] FIG. 1: schematically represents a side view of a stationary robot, a human and an inanimate object;

[0046] FIG. 2: schematically represents a top view of a mobile robot, a human and an inanimate object; and

[0047] FIG. 3: schematically represents a top view of a further mobile robot, a human and an inanimate object.

DETAILED DESCRIPTION

[0048] In the following, a method of controlling a robot, a control system for controlling a robot, and a robot comprising a control system, will be described. The same or similar reference numerals will be used to denote the same or similar structural features.

[0049] FIG. 1 schematically represents a side view of a stationary robot 10a, a human 12a and an inanimate object 12b. The robot 10a comprises a manipulator 14 and a stationary base 16a.

[0050] The manipulator 14 is movable relative to the base 16a. The manipulator 14 comprises a plurality of links and a plurality of joints. The manipulator 14 may be programmable to move in three or more axes, such as in six or seven axes. The manipulator 14 comprises a servo motor in each joint.

[0051] The robot 10a further comprises a control system 18. The control system 18 comprises a data processing device 20 and a memory 22. The memory 22 has a computer program stored thereon. The computer program comprises program code which, when executed by the data processing device 20 causes the data processing device 20 to perform, or command performance of, various steps as described herein. As shown in FIG. 1, the manipulator 14 executes a trajectory 24 according to a robot program implemented in the control system 18. The robot program comprises a reactive planner for controlling the robot 10a, e.g. based on model predictive control (MPC).

[0052] The control system 18 can control the mechanical impedance of the manipulator 14 by controlling a positional gain and a speed gain of one or more the servo motors. In this case, the positional gain corresponds to a spring constant and the speed gain corresponds to a damping factor.

[0053] The inanimate object 12b of this example is an automated guided vehicle, AGV, carrying items for a process involving the robot 10a. As shown in FIG. 1, the robot 10a works in an unstructured environment where both the human 12a and the inanimate object 12b may come into immediate proximity of the robot 10a.

[0054] The robot 10a further comprises one or more proximity sensors 26 and one or more thermal sensors 28. Although only one proximity sensor 26 and only one thermal sensor 28 are illustrated, the robot 10a may comprise a plurality of proximity sensors 26 and a plurality of thermal sensors 28, e.g. one pair of a proximity sensor 26 and a thermal sensor 28 on each link of the manipulator 14. One or more proximity sensors 26 and one or more thermal sensors 28 may also be provided on the base 16a.

[0055] Each proximity sensor 26 and each thermal sensor 28 is in signal communication with the control system 18. Each proximity sensor 26 outputs a distance value and each thermal sensor 28 outputs a temperature value. In this example, each proximity sensor 26 is a low-cost time-of-flight sensor and each thermal sensor 28 is a low-cost infrared array sensor.

[0056] As shown in FIG. 1, the human 12a is proximate to the robot 10a. The human 12a is here positioned at a distance 30 from the robot 10a. The proximity sensor 26 thereby provides a distance value indicative of a distance to the human 12a and the thermal sensor 28 thereby provides a temperature value indicative of a temperature of the human 12a.

[0057] The control system 18 compares the distance value with a distance threshold value. The distance threshold value may for example be 3 meters. The control system 18 further compares the temperature value with a temperature threshold value. The temperature threshold value may for example be 30 C.

[0058] In case the distance value is smaller than the distance threshold value, the control system 18 concludes that a human 12a or an inanimate object 12b is close to the robot 10a. In case the temperature value is larger than the temperature threshold value, the control system 18 concludes that a human 12a, and not an inanimate object 12b, is detected. Conversely, in case the temperature value is smaller than the temperature threshold value, the control system 18 concludes that an inanimate object 12b, and not a human 12a, is detected. The thermal sensors 28 thus enable a human 12a to be distinguished from an inanimate object 12b.

[0059] Even though the proximity sensors 26 and the thermal sensors 28 are low-cost sensors, the detection of a proximate human 12a can be made in a reliable manner. In fact, the simplicity of the proximity sensors 26 and the thermal sensors 28 makes the processing of the respective distance values and temperature values to be made quickly, e.g. at a high frequency. This further improves the reliability of the detection of an object and the categorization of the object as a human 12a or as an inanimate object 12b. Moreover, in this example the method does not react differently to different body parts of the human 12a. The complexity of the method can thereby be further reduced, and the reliability of the method can thereby be further increased.

[0060] The robot 10a may further comprise one or more vision sensors 32. Also, the one or more vision sensors 32 may be in signal communication with the control system 18. Each vision sensor 32 may for example be a stereo camera or a time-of-flight camera, such as an RGB-D camera. The vision sensors 32 may be used for long-distance monitoring to increase the reliability of the detection and categorization of the object as a human 12a or an inanimate object 12b. To this end, the temperature value output from the thermal sensors 28 and the distance value output from the proximity sensors 26 may be combined with a vision output from each of the vision sensors 32.

[0061] When no object is in the vicinity of the robot 10a, e.g. when the distance value to any detected object is larger than the distance threshold value, the manipulator 14 is motion controlled with a high mechanical impedance. In the motion control, the stiffness may be infinite. Should the human 12a get in the path of the manipulator 14 when executing the trajectory 24 during such motion control, the human 12a might be injured.

[0062] In case a human 12a is in proximity to the object, i.e. when the distance value is smaller than the distance threshold value and the temperature value is larger than the temperature threshold value, the control system 18 controls the robot 10a to reduce its mechanical impedance.

[0063] In this example, the mechanical impedance of the entire manipulator 14 is gradually reduced as the human 12a comes closer to the robot 10a. The mechanical impedance of the robot 10a is here changed via a software control algorithm of the robot program such that a stiffness of an impedance control of the manipulator 14 is reduced to successively lower the mechanical impedance of the manipulator 14. The control of the manipulator 14 may gradually or immediately change from motion control regime with high stiffness to a human-robot interaction mode with lower stiffness, such that a compliant behavior is obtained, when a human 12a approaches the robot 10a.

[0064] When the mechanical impedance is reduced, the manipulator 14 will be more compliant such that the human 12a cannot be injured by the manipulator 14, should the manipulator 14 contact the human 12a. The real safety of the human 12a is thereby increased. The reduced mechanical impedance of the manipulator 14 also increases the perceived safety in case the human 12a touches the manipulator 14 and feels its compliance.

[0065] In addition to a reduced mechanical impedance, a movement strategy by the reactive planner may optionally be different depending on whether a human 12a is in proximity to the robot 10a, or whether an inanimate object 12b is in proximity to the robot 10a or no object is in proximity to the robot 10a. When a human 12a is in proximity to the robot 10a, the manipulator 14 can be controlled to avoid contact with the human 12a, but with relatively low speeds and relatively high smoothness of motion, e.g. with limited acceleration. The manipulator 14 thereby moves slow and without jerky movements. This different behavior of the robot 10a further increases the perceived safety and the human 12a will not be scared.

[0066] When an inanimate object 12b is detected in proximity to the robot 10a, i.e. when the distance value is smaller than the distance threshold value and the temperature value is smaller than the temperature threshold value, the movement strategy of the robot 10a is not modified in this example. Thus, the manipulator 14 is controlled to avoid contact with the inanimate object 12b, but without reducing the mechanical impedance, with relatively high speeds and without imposing additional limitations on acceleration. Such movement strategies are previously known.

[0067] FIG. 2 schematically represents a top view of a mobile robot 10b, a human 12a and an inanimate object 12b. Mainly differences with respect to FIG. 1 will be described. The robot 10b comprises two manipulators 14 and may be a service robot. Each manipulator 14 is of the same or similar type as in FIG. 1. Each manipulator 14 comprises one or more proximity sensors 26 and one or more thermal sensors 28. The robot 10b may be referred to as a mobile manipulator.

[0068] The robot 10b comprises a movable base 16b having a traction arrangement 34. The base 16b may be an automated guided vehicle, AGV. The traction arrangement 34 is configured to drive the robot 10b over a surface, such as a floor. The traction arrangement 34 of this example comprises a plurality of driven wheels 36. A servo motor is provided for each driven wheel 36. The mechanical impedance of the traction arrangement 34 can be controlled by controlling a positional gain and a speed gain of one or more the servo motors for the driven wheels 36. In this case, the positional gain corresponds to a spring constant and the speed gain corresponds to a damping factor.

[0069] The manipulators 14 of the robot 10b are controlled in the same way as the manipulator 14 of the robot 10a when a human 12a is in proximity to the robot 10b, when an inanimate object 12b is in proximity to the robot 10b and when no object is in proximity to the robot 10b. Thus, the mechanical impedance of the manipulators 14 are reduced when a human 12a is in proximity to the robot 10b. However, in case a human 12a comes into proximity of the robot 10b, also the mechanical impedance of the traction arrangement 34 is reduced. The mechanical impedance of the entire robot 10b is thereby reduced. In case the manipulators 14 are stationary with respect to the base 16b when the base 16b moves, the human 12a can feel the resiliency of the traction arrangement 34 if contacting the robot 10b.

[0070] When a human 12a is in proximity to the robot 10b, also the traction arrangement 34 can be controlled in order to avoid contact between the robot 10b and the human 12a, but with relatively low speeds and relatively high smoothness of motion, e.g. with limited acceleration. Also, the base 16b thereby moves slow and without jerky movements. This different behavior of the traction arrangement 34 further increases the perceived safety and the human 12a will not be scared.

[0071] When an inanimate object 12b is detected in proximity to the robot 10b, i.e. when the distance value is smaller than the distance threshold value and the temperature value is smaller than the temperature threshold value, the movement strategy of the manipulators 14 and the traction arrangement 34 is not modified. Thus, the robot 10b is controlled to avoid contact with the inanimate object 12b, but without reducing its mechanical impedance, with relatively high speeds and without imposing additional limitations on acceleration.

[0072] FIG. 3 schematically represents a top view of a further mobile robot 10c, a human 12a and an inanimate object 12b. Mainly differences with respect to FIG. 2 will be described. The robot 10c in FIG. 3 differs from the robot 10b in FIG. 2 in that the robot 10c in FIG. 3 does not comprise any manipulator. When the mechanical impedance of the robot 10c is reduced, the mechanical impedance of the traction arrangement 34 is reduced.

[0073] While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.