20_1025 Torque-Bounded Admittance Control Realized by a Set-valued Algebraic Feedback

Details can be found in:
Ryo Kikuuwe: "Torque-Bounded Admittance Control Realized by a Set-Valued Algebraic Feedback," IEEE Transactions on Robotics, Vol.35, No.5, pp.1136-1149, October 2019.
https://doi.org/10.1109/TRO.2019.2920069
https://home.hiroshima-u.ac.jp/kikuuwe/pub/19_tro_aut.pdf

Transcript

1. 1 A presentation for IEEE/RSJ IROS2020 Torque-Bounded Admittance Torque-Bounded Admittance Control Realized by a Control Realized by a Set-Valued Algebraic Feedback Set-Valued Algebraic Feedback Hiroshima University, Japan Ryo Kikuuwe https://home.hiroshima-u.ac.jp/kikuuwe/ https://www.youtube.com/user/kikuuwe/ Presentation for IROS 2020
2. 2 A presentation for IEEE/RSJ IROS2020 environment environment position contact force position command position controller position controller torque command Proxy Proxy external force ＋ ＋ ＋ Admittance Control Admittance Control  AKA: “Position-based Impedance Control”  Realizes specified mechanical impedance on the end-effector. f Mv Bv  Requires force sensor.  If Robot tracks a Proxy accurately, robot’s dynamics becomes close to the “proxy” dynamics  Robot’s dynamics is suppressed by position controller.  Suited for robots with high-ratio gear boxes & large inertia.
3. 3 A presentation for IEEE/RSJ IROS2020 Flaw of admittance control Flaw of admittance control  Responds only to force sensor inputs.  Does not react to out-of- sensor contacts. (Position controller resists to it.)  It may cause damage or injury. environment environment position contact force position command position controller position controller torque command Proxy Proxy external force ＋ ＋ ＋
4. 4 A presentation for IEEE/RSJ IROS2020 What if actuator torques are limited? What if actuator torques are limited?  Still unsafe!  Proxy does not respond to the out-of-sensor contact Once ⇒ the force is removed, Robot snaps back to Proxy.  Holding Robot and pushing the force sensor results in unpredictable behavior environment environment position contact force position command position controller position controller torque command Proxy Proxy external force ＋ ＋ ＋
5. 5 A presentation for IEEE/RSJ IROS2020 Contribution Contribution  New admittance control to which torque limits can be set.  Below the limits, it’s equivalent to conventional admittance control.  There is no snapping back even after torque saturation
6. 6 A presentation for IEEE/RSJ IROS2020 Conventional Admittance Controller Conventional Admittance Controller  It consists of a “Proxy Dynamics” and “Position Controller”  Robot position qs does not influence Proxy position qx . → External force may pull Robot apart from Proxy. environment environment position contact force position command position controller position controller torque command Proxy Proxy external force ＋ ＋ ＋ ↓ position controller ←proxy dynamics =
7. 7 A presentation for IEEE/RSJ IROS2020 Proposed Method Proposed Method  Includes a normal-cone feedback.  Now it is Diff. Alg. Inclusion with unknowns qx and ¿.  It’s an algebraic loop without latency ←proxy .. ↓ position controller environment environment position contact force position command position controller position controller torque command Proxy Proxy external force ＋ ＋ ＋ －
8. 8 A presentation for IEEE/RSJ IROS2020  (1) does not permit ¿ outside [{F, F ].  As far as , it’s equivalent to normal admittance control.  When , the proxy acceleration is determined so that (2) with holds true. (2) (1) Property of this DAI Property of this DAI  When the torque is saturated, the normal- cone term acts to pull the robot to the proxy, holding the proxy near the robot.
9. 9 A presentation for IEEE/RSJ IROS2020 Implementation to discrete time Implementation to discrete time  Discretization with implicit Euler method (e.g., 　　　　　　　　　　　　 )  Analytical solution  We get an ordinary algorithm without set-valuedness
10. 10 A presentation for IEEE/RSJ IROS2020 The Algorithm The Algorithm  Constants:  No iterative computation. Computationally cheap.
11. 11 A presentation for IEEE/RSJ IROS2020 Implementation Implementation  New controller with the torque limits 1.5Nm to 6Nm plus gravity+friction compensators  With the friction compensator developed by Iwatani & Kikuuwe (2017, SICE-JCMSI)
12. 12 A presentation for IEEE/RSJ IROS2020  Pushing the link  [C] Robot departs from proxy, and snaps back later  [N] Proxy follows robot Experiments & Results Experiments & Results  [C] Conventional Method  [N] New method  Pushing the link with holding force sensor  [C] Proxy moves away and Robot tries to chase it.  [N] Proxy stays with Robot.
13. 13 A presentation for IEEE/RSJ IROS2020 Concluding Remarks Concluding Remarks  We’ve presented a torque-bounded admittance controller that doesn’t result in unsafe behavior.  It responds to measured forces with specified impedance. It yields to out-of-sensor forces larger than the actuator force.  Will be useful for direct teaching to robots and physical human-robot coordination.