Lecture 9: Teleoperation

Transcription

1 ME 327: Design and Control of Haptic Systems Autumn 2018 Lecture 9: Teleoperation Allison M. Okamura Stanford University

2 teleoperation history and examples

3 the genesis of teleoperation? a Polygraph is a device that produces a copy of a piece of writing simultaneously with the creation of the original, using pens and ink. Famously used by Thomas Jefferson ~1805. Typically uses a pantograph mechanism: a five-bar linkage with parallel bars such that motion at one point is reproduced at another point

4 teleoperation history first master-slave manipulator: 1948, Ray Goertz, U.S. Atomic Energy Commission goal was to protect workers from radiation, while enabling precise manipulation of materials a device which is responsive to another device is termed a "slave" and the controlling device is termed a "master at first, mechanical linkages and cables 1954: electrical and hydraulic servomechanisms 1960s: closed-circuit television and head-mounted displays (HMDs)

5 bilateral control = force feedback inherent in mechanical teleoperators forces at the slave endeffector are reflected to the master end-effector displacements produced at the slave end-effector produce a displacement at the master endeffector

6 modern telemanipulators undersea: exploration and oil acquisition space 1967: Surveyor III landed on the surface of the Moon (a few seconds delay in the two-way transmission to earth of commands and information) 1976: Viking spacecraft, landed on Mars was programmed to carry out strictly automated operations Shuttle Remote Manipulator System (SRMS): retrieves satellites and place them in the cargo bay; mobile work platform for astronauts during space walks

7 even more dexterous teleoperation Robonaut Robot Systems Technology Branch at NASA's Johnson Space Center purpose is to replace astronauts in dangerous missions, such as space walk, on the space shuttle and/or the space station both autonomous operation and teleoperation are being developed

8 surgical robotics (e.g., da Vinci Surgical System) images and video Intuitive Surgical, Inc. 2012

9 simple system example Abbott and Okamura 2004

10 simple system example soft virtual wall Abbott and Okamura 2004

11 teleoperation controllers

12 unilateral teleoperator model modified from Kuchenbecker Ph.D. Thesis (2006)

13 bilateral teleoperator model (using position) modified from Kuchenbecker Ph.D. Thesis (2006)

14 bilateral teleoperator model (using force) modified from Kuchenbecker Ph.D. Thesis (2006)

15 typical slave robot controller this is a proportional-derivative controller, which attempts to make the slave follow the master s position and velocity f as (t) =k ps (x m x s )+k ds (ẋ m ẋ s ) f as (t) x m x s slave actuator force position of master position of slave k ps k ds slave proportional gain slave derivative gain for each haptic loop, the master s motion is recorded and the slave robot attempts to follow the master

16 master robot controller for unilateral teleoperation f am =0 f am (t) master actuator force the force applied by the master actuator (if it exists) is zero

17 master robot controller for bilateral teleoperation (using position) f am (t) =k pm (x s x m )+k dm (ẋ s ẋ m ) f am (t) x m x s master actuator force position of slave position of master k pm k dm master proportional gain master derivative gain for each haptic loop, the slave s motion is recorded and the master robot attempts to follow the slave

18 master robot controller for bilateral teleoperation (using force) f am (t) =f e f am (t) f e master actuator force measured environment force for each haptic loop, the force between the slave and the environment is measured, and the master robot outputs this amount of force

19 discussion for these control laws to work, should the master and/or slave be of the admittance or impedance type? motion scaling: why would you want this, and how would you change the control laws to accomplish this? force amplification: why would you want this, and how would you change the control laws to accomplish this?

20 implementation summary slave robot controller f as (t) =k ps (x m x s )+k ds (ẋ m ẋ s ) unilateral teleoperation: f am =0 master robot controller bilateral teleoperation (position-exchange): f am (t) =k pm (x s x m )+k dm (ẋ s ẋ m ) bilateral teleoperation (position forward, force feedback): f am (t) =f e

21 discussion what might limit the values of the controller gains that you can choose, and how does this relate to force feedback for virtual environments? what are the comparative advantages and disadvantages of position- and force-based bilateral teleoperation?

22 teleoperator transparency

23 primary teleoperation performance metrics tracking the ability of the slave to follow the master transparency (for bilateral teleoperation only) many definitions, but a popular one is whether the mechanical impedance felt by the user is the same as the impedance of the environment

24 discussion what factors might affect tracking? what factors might affect transparency?

25 Z-width for teleoperators Christiansson et al. 2008

26 system structure

27 transparency requirement for perfect transparency (impedance reflection): Z e (s) = F e(s) X s (s) Z felt (s) = F h(s) X m (s) Z e (s) = Z felt (s) a more strict requirement would be: F h (s) = F e (s) and X m (s) = X s (s)

28 transparency are our three controllers transparent? you can test each one, using: F h = X m Z m + F am F e = X s Z s + F as what assumptions are needed to achieve perfect transparency?

29 network block diagram impedance transmitted to the operator impedance transmitted to the environment Hashtrudi-Zaad & Salcudean, 2002

30 transparency using this notation we want impedance matching: or and perhaps kinematic correspondence as well: Hashtrudi-Zaad & Salcudean, 2002

31 two-port network model there are four types here is one (a hybrid model): the hybrid parameters hij are functions of the master and slave dynamics and their control parameters the transmitted impedances can be computed:

32 the transmitted impedances can be computed: but we don t know Ze and Zh! so impedance matching can only be guaranteed when this will enforce and

33 kinematic correspondence assuming no position or force scaling, the velocity of the human and the environment are this also requires certain h parameters Hashtrudi-Zaad & Salcudean, 2002

34 total transparency to enforce perfect impedance reflection and kinematic correspondence we must have: but what are these h s?? Hashtrudi-Zaad & Salcudean, 2002

35 a more detailed block diagram we are ignoring time delay blocks Hashtrudi-Zaad & Salcudean, 2001

36 closed-loop equations master: slave: where: Z cm = C m + Z m Z cs = C s + Z s Hashtrudi-Zaad & Salcudean, 2001

37 transmitted impedances you can match these equations to the equations with the h s to see the relationship between the h s and the control parameters of the system Hashtrudi-Zaad & Salcudean, 2001

38 transparency condition If C 1 C 6 are not functions of Z h and Z e and (C 2,C 3 ) (0,0) physical interpretation: the master and slave dynamics have to be cancelled out by inverse dynamics and the feedforward forces have to match the net forces exerted by the operator on the environment Hashtrudi-Zaad & Salcudean, 2001