Telerobotic system

• US 5,266,875 A
• Filed: 05/23/1991
• Issued: 11/30/1993
• Est. Priority Date: 05/23/1991
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Niemeyer, Gunter D., Slotine, Jean-Jacques E.
• Primary Examiner(s): Ip, Paul
• Application Number:
  US07/704,946
• Time in Patent Office: 922 Days
• Field of Search: 318/560-632, 318/660, 395/80-99, 901/3, 901/5, 901/9, 901/12, 901/13, 901/15, 901/17-20
• US Class Current: 318/568.11
• CPC Class Codes: B25J 9/1689 Teleoperation

Abstract

A telerobotic system provides a means for transmitting data between a master and a remote slave unit with a time delay therebetween. The master and slave unit form a closed loop in which motion commands are transmitted from the master to the slave and force data is transmitted back from the slave to the master. Stability is obtained over time delay by means of transforming the motion data into a wave representation in transmission between the master and slave. The signal from the master to the slave may be characterized generally as u=F+bx while the signal from the slave to the master may be characterized generally as v=F-bx where F equals the force imparted by the environment, x equals the velocity commanded by the master, and b is a characteristic wave impedance.

Claims

1. A system for transmitting data representing an action and responsive data representing a reaction in the presence of a time delay comprising:

means for transmitting data between a first point and a remote second point, including a time delay therebetween;

means for transforming action command at a first point into data in a form of a first wave representation;

means for receiving and transforming the first wave representation into an action command at a second remote point;

means at the second remote point for detecting an action state resulting from the action command;

means for transforming the action state into data in a form of a second wave representation;

means at the first point for transforming a received second wave representation into a sensed state; and

wherein the wave representation of the action command comprises a wave amplitude u and the wave representation of the action state comprises a wave amplitude v and wherein each of u and v comprise the equations ##EQU20## wherein b equals a characteristic wave impedance, F equals a force transmitted as the action state and x equals a velocity transmitted as the action command.

2. A system as set forth in claim 1 wherein the first point includes a master manipulator unit for interface with an operator and the second point includes a remote slave manipulator unit for interacting with an environment.

3. A system as set forth in claim 1 wherein at least one of the master manipulator unit and the remote slave manipulator unit include an impedance controller for matching impedance thereof to that of the characteristic wave impedance b.

4. A system as set forth in claim 3 further comprising means for transforming each of the wave amplitudes u and v into position-relative values based upon sensed force information at each of the master and the remote slave units.

5. A system as set forth in claim 1 wherein the time delay between the first point and the remote second point includes a time delay resulting from a filtering element.

6. A method of transmitting data representing an action an responsive data representing a reaction in the presence of a time delay comprising the steps of:

transmitting data between a first point and a remote second point having a time delay in transmission therebetween;

transforming action commands at the first point into data in a form of a first wave representation;

receiving and transforming the wave representation into an action command at the second remote point;

detecting an action state resulting from an action command at the second remote point;

transforming the action state into data in a form of a second wave representation;

transforming a received second wave representation into a sensed state at the first point; and

wherein the step of transforming the action command includes defining of an amplitude u and the step of transforming an action state includes defining an amplitude v wherein each of u and v comprise the equations ##EQU21## wherein b equals a characteristic wave impedance, F equals a force transmitted as the action state and x equals a velocity transmitted as the action command.

7. A method as set forth in claim 6 wherein the first point includes a master manipulator unit for interfacing with an operator and the second point includes a remote slave manipulator unit for interacting with an environment.

8. A method as set forth in claim 6 further comprising matching impedance of at least one of the first point and the second point to the characteristic wave impedance.

9. A method as set forth in claim 8 further comprising tuning of the impedance of at least one of the first point and the second point to optimize system response.

10. A method as set forth in claim 9 wherein the step of tuning includes controlling impedance of a manipulator at at least one of the first point and the second point, the controlling including defining a transfer function of force transmitted as the action state versus desired velocity input as the action command x_d equal to:

##EQU22## wherein p is a Laplace operator, K is a position gain equal to a predetermined bandwidth of the manipulator times a controller damping value B, and wherein B is an environmental damping value relative to the manipulator D, m is an equivalent mass of the manipulator and wherein R is a differential damping value equal to b-B.

11. A method as set forth in claim 6 further comprising the step of transforming each of the wave amplitudes u and v into position-relative values based upon sensed force information at each of the first point and the second point.

12. A method of transmitting data and of receiving responsive data in the presence of a time delay comprising:

providing a force value and a position value input at a first location;

transforming a combination of the force value and the position value at the first location into a first wave representation;

transmitting the first wave representation to a second location remote from the first location and receiving the first wave representation at the second location;

establishing one of a force value and a position value at the second location;

deriving one of a new force value and a new position value at the second location based upon a combination of the first wave representation with, respectively, one of the established position value and the established force value;

transforming one of a combination of the new force value and the established position value and a combination of the established force value and the new position value at the second location, respectively, into a second wave representation;

transmitting the second wave representation from the second location and receiving the second wave representation at the first location;

establishing one of a force value and a position value at the first location; and

deriving one of a new force value and a new position value based upon a combination of the second wave representation with, respectively, one of the established position value and the established force value at the first location, respectively.

13. A method as set forth in claim 12 wherein the first wave representation comprises a wave amplitude u and the second wave representation comprises a wave amplitude v and wherein each of u and v comprise the equations ##EQU23## wherein b equals a characteristic wave impedance, F equals a provided force value input and x equals a velocity derived from a provided position value input.

14. A method as set forth in claim 12 wherein the second wave representation comprises a wave amplitude u and the first wave representation comprises a wave amplitude v and wherein each of u and v comprise the equations ##EQU24## wherein b equals a characteristic wave impedance, and F and x equal, respectively, one of the new force value and a velocity derived from the established position value at the second location and the established force value and a velocity derived from the new position value at the second location.

15. A system as set forth in claim 12 wherein the first wave representation comprises a wave amplitude u and the second wave representation comprises a wave amplitude v and wherein each of u and v comprise the equations ##EQU25## wherein b equals a characteristic wave impedance, and F and x equal, respectively, one of the new force value and a velocity derived from the established position value at the first location and the established force value and a velocity derived from the new position value at the first location.

16. A method as set forth in claim 12 further comprising filtering force and position values transmitted between the first location and the second location.

17. A telerobotic system operating in the presence of a time delay comprising:

a master unit that provides a force value and a position value input;

a wave transformation element that combines the force value and the position value from the master unit into a first wave representation;

a transmitter that transmits the first wave representation from the master unit to a remote slave unit, the slave unit receiving the first wave representation and the slave unit establishing one of a present force value and a present position value at the slave unit;

a force value updating element at the slave unit that derives one of a new force value and a new position value based upon a combination of the first wave representation with, respectively, one of the established present position value and the established present force value at the slave unit;

a wave transformation element at the slave unit that transforms one of a combination of the new force value and the established present position value and a combination of the established force value and the new position value at the slave unit, respectively, into a second wave representation;

a transmitter at the slave unit that transmits the second wave representation from the slave unit to the master unit, the master unit establishing one of a present force value and a present position value at the master unit; and

a force value updating element at the master unit that derives one of a new force value and a new position value at the master unit based upon a combination of the second wave representation with, respectively, one of the established present position value and the established present force value at the master unit, respectively.

18. The telerobotic system as set forth in claim 17 wherein each of the first and second wave representations are based upon a characteristic wave impedance b.

19. The telerobotic system as set forth in claim 18 wherein each of the master unit and the slave unit include a manipulator that interacts with an environment.

20. The telerobotic system as set forth in claim 19 further comprising an impedance controller located between the manipulator and the slave unit, the impedance controller matching the impedance b to a characteristic impedance of the manipulator.

21. The telerobotic system as set forth in claim 20 wherein the impedance controller controls impedance based upon gains that are selected based upon inertial differences between the manipulator of the master unit and the manipulator of the slave unit, environmental damping acting upon the manipulator of the slave unit, internal impedance controller damping, and internal manipulator frictional damping.

22. The telerobotic system as set forth in claim 18 further comprising a prediction element located at each of the master unit and the slave unit, the prediction unit providing at least one of a predicted new position value and a predicted new force value to be received by one of the master unit and the slave unit in response, respectively, to data transmitted by one of the slave unit and the master unit.