Trajectory tracking errors resulting from the application of various controllers have been experimentally determined on the MIT Serial Link Direct Drive Arm. The controllers range from simple analog PD (proportional-derivative) control applied independently at each joint to feedforward and computed torque methods incorporating full dynamics. It was found that trajectory tracking errors decreased as more dynamic compensation terms were incorporated. There was no significant difference in trajectory tracking performance between the feedforward controller using independent digital servos and the full computed torque controller. Implementing the model-based controller highlights the need for accurate control of joint torque, accurate joint position and velocity sensing, and adequate sampling rates.>

Work on building robot models to be used in designing model-based controllers is described. Various algorithms are presented estimating the kinematic, link-inertial, and load-inertial parameters. It is shown experimentally that accurate estimates can be obtained automatically using sensor data taken during movement. The algorithms have been implemented on the MIT Serial Link Direct Drive Arm.>

For pt.I see ibid., p.1374-9 (1988). Work on model-based control with the MIT Serial Link Direct Drive Arm is described. It is shown that model-based control leads to performance superior to control not based on carefully constructed models. Trajectory control, trajectory learning, and force control are treated. A new type of trajectory learning is considered in which a robot fine-tunes one particular trajectory through repetition. Various experiments with the direct drive arm are reported to validate the importance of model-based control.>

Trajectory tracking errors resulting from the application of various controllers have been experimentally determined on the MIT Serial Link Direct Drive Arm. The controllers range from simple analog PD control applied independently at each joint to feedforward and computed torque methods incorporating full dynamics. It was found that trajectory tracking errors decreased as more dynamic compensation terms were incorporated. There was no significant difference in trajectory tracking performance between the feedforward controller using independent digital servos and the full computed torque controller.

Robots in force control mode often become unstable during contact with stiff environments, due mainly to the high gain nature of wrist force-sensor feedback. To achieve stable force control, we propose an essential reliance on fast open-loop joint torque control, and relegate tip force sensor feedback to a slow loop to maintain accuracy. Dynamic stability is analyzed with a simple model of the robot and its environment. The analyses are verified by single-link experiments on the MIT Serial Link Direct Drive Arm.

In active force or compliance implementations for multi-link manipulators, there is typically a kinematic coordinate transformation in the feedback path. A coordinate transformation will affect the dynamics of the closed-loop system and possibly make it unstable. It is shown that the hybrid force/position control method of Raibert and Craig (1981) exhibits such kinematically induced instabilities for revolute manipulators, whereas other force control methods, such as the stiffness control and the operational space methods, do not. Both theoretical analyses and experimental results on the MIT Serial Link Direct Drive Arm are given.

Trajectory tracking errors resulting from the application of various controllers have been experimentally determined on the MIT Serial Link Direct Drive Arm. The controllers range from simple PD control applied independently at each joint to feedforward control incorporating full dynamics followed by a separate PD control loop. It was found that trajectory tracking errors decreased as more feedforward terms were incorporated.

This correspondence examines integrated-circuit logarithmic arithmetic units which include adders, subtracters, multipliers, and dividers. The design of these arithmetic units is reviewed, and an example arithmetic unit which performs multiplication followed by addition is designed in detail. The design results are used to develop a size and speed comparison of integrated-circuit logarithmic and fixed-point arithmetic units. This comparison is exercised through a video signal processing example. It is concluded from this comparison that logarithmic arithmetic units are smaller than, and as fast as, fixed-point arithmetic units with comparable capabilities in digital signal processing applications characterized by large dynamic range and moderate computational accuracy requirements. Further, this comparison quantitatively illustrates the interaction of digital-signal-processing and integrated-circuit issues in the design of special-purpose digital signal processors.