Continuous Feedforward Control Research Articles

Voluntary Control of Residual Antagonistic Muscles in Transtibial Amputees: Reciprocal Activation, Coactivation, and Implications for Direct Neural Control of Powered Lower Limb Prostheses.

Residual ankle muscles (i.e., previously antagonistic ankle muscles) of transtibial amputees are a potential source for continuous feedforward control of powered ankle prostheses using proportional myoelectric control. The ability for transtibial amputees to use their residual ankle muscles for two control input degrees of freedom (i.e., two independent myoelectric control input sources) for direct neural control depends on the ability for amputees to generate varying magnitudes of reciprocal activation and coactivation using their residual ankle muscles, which is not well understood. In this paper, we aimed to fill this knowledge gap. We asked 12 transtibial amputees to control the 2-D movement of a computer cursor using continuous proportional myoelectric control via their residual plantar flexor and residual dorsiflexor muscles to define their reachable 2-D control input space. The x-y position of the computer cursor was directly proportional to the independent continuous myoelectric control signals from the residual lateral gastrocnemius (x-axis) and the residual tibialis anterior (y-axis) where the limits of each axis were 0%-100% maximum voluntary activation of the corresponding residual muscle. Our results show that the reachable control input space varied widely across amputee subjects ranging from 38% to 81% of the maximum possible control input space. The cumulative time for the amputee subjects to saturate their reachable control input space ranged from 1.95 to 6.85 min. The amputee subjects used different residual muscle activation patterns and coordination strategies to expand their reachable control input space depending on their ability to perform coactivation and reciprocal activation using their residual plantar flexor and dorsiflexor muscles. The future development of powered lower limb prostheses using direct continuous proportional myoelectric control via residual muscles (e.g., for direct voluntary control of prosthesis joint impedance) should consider how an amputee user's immediately accessible residual muscle activation patterns and reachable 2-D control input space may affect their learning and performance.

Microprocessor-Based Decoupled Control of Manipulator Using Modified Model-Following Method with Sliding Mode

A methodology of discontinuous feedback and continuous feedforward control is developed to achieve accurate decoupled tracking in a class of nonlinear, time varying systems in the presence of disturbances, parameter variations and nonlinear dynamic interactions. The method is based on an improved variable structure control with a sliding mode.

Improved Sliding Mode Method Applied to Digital Decoupled Water Level Control for Two Tanks Connected with Pipes

A methodology of discontinuous feedback and continuous feedforward control is developed to achieve accurate decoupled tracking in a class of nonlinear systems in the presence of disturbances and parameter variations. The method is based on an improved variable structure control with a sliding mode. First, a desired output time response (forced model) is generated in time series with a microprocessor. Then discontinuous feedback and continuous feedforward controls are applied in order to force the output to track its desired time response. By introducing this modified model following control, the error between the output of the plant and model is made very small. Thus this mitigates the extent of undesirable chattering due to switching delays, neglected small time constants, etc. The convergence of the error state to the origin is proved by using “direct method of Liapunov.” With the rapid progress in microelectronics and powerelectronics high-performance actuators, sensors are now available. Therefore the proposed control strategy can be easily implemented resulting in revolutionary high-quality control in processes.The methodology is practically applied to decoupled water-level controls for two tanks connected with pipes, in which water-levels are interacting on one another. All the control strategies are implemented by a high performance microprocessor which is now available at reasonable cost. It is found that this novel controller obtained performs extremely satisfactorily and is superior to the “conventional” controller for the process. In addition, the controller can be simply designed, since it does not require accurate modeling. but it is sufficient to know only the bounds of model parameter values and the magnitudes of the disturbances.

Microprocessor-Based Decoupled Control of Manipulator Using Modified Model Following Method with Sliding Mode

A methodology of discontinuous feedback and continuous feedforward control is developed to achieve accurate decoupled tracking in a class of nonlinear time varying systems in the presence of disturbances, parameter variations and nonlinear dynamic interactions. The method is based on an improved variable structure control with a sliding mode. The convergence of the error state to the origin is proved by using the "direct method of Liapunov".Then the developed method is practically applied to decoupled tracking control for a two-degrees-of-freedom manipulator. The joint position trajectories are observed to be smooth and to track the desired trajectories accurately.