Most robotic manipulators use harmonic drives.  A harmonic drive is a compact gearing system that achieves very large gear ratios, at the price of elasticity.  For instance, large harmonic drives cause Canadarm and Canadarm2 to have a tremendous amount of joint flexibility.  Chris is interested in precision control of rigid-link flexible-joint robots, where the tip position is kept within millimeter accuracy by actively compensating for all the flexibility in the joints.

Chris has a flexible-joint robot built by Quanser in his lab (pictured here) where the elasticity comes from actual springs in the joints. This is an excellent platform for testing advanced control systems.

Here are links to some of the group's publications on control of flexible-joint robots.

Macnab Publications Macnab, C.J.B. Finding a near-optimal neural-adaptive control solution without increasing the training time.
    Conference on Decision and Control
    (Melbourne, Australia) pp. 3316-3323, 2017

Macnab, C.J.B. and S. Razmi, Control of a flexible-joint robot using a stable adaptive introspective CMAC.
    IEEE Conference on Systems, Man, and Cybernetics
    (Banff), pp. 1546-1551, 2017.

Macnab, C.J.B. Preventing overlearning in CMAC by using a short-term memory.
    International Journal of Fuzzy Systems
    DOI: 10.1007/s40815-016-0275-9, 2017.

Macnab, C.J.B. Creating a CMAC with overlapping basis functions in order to prevent weight drift.
    Soft Computing
    Vol 21, No. 16, pp. 4593-4600, 2017.

R. L'Orsa and C. J. B. Macnab. Experimental evaluation of adaptive CMAC haptic control for teleoperation of compliant-joint manipulators.
    IEEE International Symposium on Industrial Electronics
    (Edinburgh), pp. 1087 - 1092, 2017.

Macnab, C.J.B.  Neural-adaptive backstepping for flexible-joint robots with neither extra parameters, extra networks, nor robust terms
    IEEE Conference on Industrial Technology
    (Toronto), pp. 854-859, 2017.

Masaud, K. and C.J.B. Macnab. Preventing bursting in adaptive control using an introspective neural network algorithm,
    Vol. 136, pp. 300–314, 2014.

Richert, D., K. Masaud, and C. J. B. Macnab. Discrete-time weight updates in neural-adaptive control.
    Soft Computing
    Vol. 17, No. 3, pp. 431-444, 2013.

Masaud, K., and C.J.B. Macnab,  Stable fuzzy-adaptive control using an introspective algorithm,
    Proc. American Control Conference,
    (Montreal) pp. 5622 -5627, June 2012

Macnab, C.J.B., Neural-adaptive control using alternate weights.
     Neural Computing and Applications,
    Vol. 20, No. 2, pp. 211-231, 2011.

Macnab, C.J.B.  Improved output tracking of a flexible-joint arm using neural networks.
    Neural Processing Letters,
    Vol. 32 (2), pp. 201-218, 2010.

Macnab, C.J.B,   Preventing bursting in approximate adaptive control when using local basis functions.
    Fuzzy Sets and Systems
    Vol. 160 (4), pp. 439-462, 2009

Macnab, C.J.B,  A new robust weight update for multilayer-perceptron adaptive control.
    Control and Intelligent Systems
    Vol. 35, No. 3, pp. 279-288, 2007.

Macnab, C.J.B, Robust associative-memory adaptive control in the presence of persistent oscillations.
    Neural Information Processing Letters and Reviews,
    10(12), pp. 277-287, 2006.

Macnab, C.J.B., Direct neural-adaptive control with quantifiable bounds and improved performance.
    Int. Joint Conference on Neural Networks,
    (Vancouver),  pp. 4456- 4462, 2006.

Macnab, C.J.B, A new robust weight update for neural-network control.
     Proc. IASTED International Conference on Intelligent Systems and Control
     (Cambridge, Mass.) pp. 360-367, 2005.

Macnab, C.J.B., Local basis functions in adaptive control of elastic systems.
     Proc. IEEE International Conference on Mechatronics and Automation
     (Niagara Falls) pp. 19 - 25, 2005.

Macnab, C.J.B., Getting weights to behave themselves: Achieving stability and performance in neural-adaptive control when inputs oscillate.
    Proc. American Control Conference
    (Portland, Oregon) pp. 3192 - 3197, 2005. 

Macnab, C.J.B., D'Eleuterio, G.M.T., and Meng, M., CMAC neurocontrol of elastic-joint robots using backstepping with tuning functions.
    Proc. IEEE International  Conference on Robotics and Automation
    (New Orleans), pp. 2679 - 2686, 2004.

Macnab, C.J.B., D'Eleuterio, G.M.T., Neuroadaptive control of elastic-joint robots using robust performance enhancement.
    vol. 19, no. 6,  pp. 619-629, Sept. 2001.

Macnab, C.J.B., D'Eleuterio, G.M.T., Discrete-time Lyapunov design for neuroadaptive control of elastic-joint robots.
    International Journal of Robotics Research
    vol. 19, no. 5,   pp. 511-525, May 2000.

Macnab, C.J.B., D'Eleuterio, G.M.T., Meng, M., Using backstepping for control of elastic-joint robots with smaller gear ratios.
    Proc. IEEE Canadian Conference on Electrical and Computer Engineering
    (Edmonton, Alberta), pp. 873 - 878, 1999.

Macnab, C.J.B., D'Eleuterio, G.M.T., Stable, on-line learning using CMACs for neuroadaptive tracking control of flexible joint manipulators.
    Proc. IEEE International Conference on Robotics and Automation
    (Leuven, Belgium) 1, pp. 511-517, 1998.