Ty A. Lasky

Robust independent joint controller design for industrial robot manipulators

A novel approach is presented for the design of simple robust independent joint controllers for industrial robot manipulators. In this approach, each joint actuator is treated as a simple inertial system plus a disturbance torque representing all the unmodeled dynamics. By a very simple algorithm, the disturbance is instantly estimated and rejected, thus allowing a simple proportional-derivative (PD) control scheme to be used. The stability of the proposed control law is analyzed. Experimental evaluations of the controller on a microcomputer-controlled PUMA 560 arm were performed. It is shown that the control scheme is simple and practical and that it can be easily implemented on an industrial manipulator presently in use. >

On force-tracking impedance control of robot manipulators

A reference force-tracking impedance control system is proposed, consisting of a conventional impedance controller in the inner-loop and a trajectory modifying controller in the outer-loop for force-tracking. The design of the outer-loop is presented and the stability of the two-loop control system is analyzed. A computationally efficient control algorithm for the inner-loop is suggested. Simulation results are presented. The controller is able to achieve excellent position and force-tracking with unknown environment stiffness and the presence of a burr on the tracking surface.<<ETX>>

Design and Implementation of a Mechatronic, All-Accelerometer Inertial Measurement Unit

This paper discusses the design, calibration, simulation, and experimental validation of a kinematically redundant inertial measurement unit that is based solely on accelerometers. The sensor unit comprises 12 accelerometers, two on each face of a cube. The location and direction of the sensors are determined so as to locally optimize the numerical conditioning of the system of governing kinematic equations. The orientational installation error of each sensor is identified by off-line iterative processing of the gravitational acceleration measurements made at a number of known orientations of the unit, thus allowing subsequent calibration. Furthermore, a novel procedure is developed through which the acceleration measurements can be used to directly determine the body angular velocity; this results in a major accuracy improvement over similar works whereby the angular velocity is obtained via integrating the angular acceleration. Experimental results are presented to validate the methodology, design, and implementation.

Robust independent robot joint control: design and experimentation

An approach is presented for the design of simple robust independent joint controllers which result in linear decoupled joint motions. In this approach each joint is treated as a simple inertial systems plus a disturbance torque representing all the unmodeled dynamics. By means of a very simple procedure, the disturbance is instantly estimated and rejected, thus allowing simple PD control to be used. The controllers are inherently robust. Experimental evaluations of the controller on a PUMA 560 are are performed, and the experimental results are presented.<<ETX>>

Improved velocity estimation for low-speed and transient regimes using low-resolution encoders

This paper presents a new estimation method, entitled the asynchronous sampling pulse method (ASPM), for determining velocity in systems with low but variable speeds, and/or with low-resolution encoders. The ASPM forces the estimator procedure to synchronize with the actual encoder pulse input, thus eliminating encoder positioning error independent of target velocity variations. This method is based on using an auxiliary sampling period to measure the time interval between the moment of encoder input and the control sampling instant, and its precision is shown to be dependent only on this auxiliary sampling period. Thus, the ASPM improves over existing methods in which estimator performance is dependent on both target acceleration and encoder resolution. Simulation and experimental results are used to verify the method.

Kinematics and Efficiency Analysis of the Planetary Roller Screw Mechanism

This paper analyzes the kinematics and the efficiency of the planetary roller screw mechanism (RSM) to provide a fundamental basis to support its various applications. The mechanical structure and practical advantages are presented in comparison with the conventional ball screw mechanism (BSM). Kinematic analysis involves derivation of the angular and axial motions, as well as the development of the slip pattern between the contacting components. Results show that for any motion of the RSM slip always occurs. Kinematic analysis including elastic deformation is also presented. The load carrying capacity and efficiency of the RSM are derived based on geometric and equilibrium conditions, and the results are compared with the BSM.

Sensor-based path planning and motion control for a robotic system for roadway crack sealing

Discusses a path planning and control method developed for robotic application in roadway crack sealing. Application of autonomous robotics to this operation requires a path planning system that can take data representing roadway cracks from an external sensor, extract connected crack paths, and link paths together to form the Cartesian motion for the robotic system used to seal the crack. Since the operation is performed in an online fashion, the path planning system has to perform kinematic computations based on dead-reckoning data to update the crack profile as the crack sealing vehicle is moving. Stringent requirements are placed on the controller by the errors inherent in the global path generation, along with the fact that to avoid kinematic singularities, the manipulator used is kinematically redundant. The system developed uses a robust controller known as the simplified Cartesian computed torque (SCCT) to guide the end-effector, along with a compliance loop to move the desired trajectory over the crack, while also addressing kinematic redundancy through application of the weighted generalized inverse Jacobian. The contributions of the paper are in developing practical applications of image processing techniques to extract path locations and determine the appropriate Cartesian end-effector paths, as well as the development of a simple but robust compliant redundant robot controller, all for use in the unstructured environment encountered in highway maintenance operations. The system described has been implemented as part of a prototype automated crack sealing machine. Sample results for actual highway data are included.

A mechatronic sensing system for vehicle guidance and control

Magnetic sensing is used for control and guidance in intelligent transportation systems (ITS). This includes vehicle applications such as lane-keeping in intelligent cruise control as well as driver assistance in highway maintenance functions such as snow removal. This paper presents a new mechatronic magnetic sensing system for ITS. The new system has several advantages both in terms of its hardware design and its underlying reference detection algorithms, providing a significant improvement in performance, maintainability, and upgradability over existing systems. It is a mechatronic system in that it combines mechanical position sensing with electronics implementation of the hardware and the underlying algorithms.

Kinematically-Redundant Variations of the 3-RRR Mechanism and Local Optimization-Based Singularity Avoidance

Abstract To avoid the singular loci of the 3-RRR mechanism that exist within its workspace, this paper applies kinematic redundancy. First, three feasible kinematic redundancy configurations for the 3-RRR mechanism are presented and singularity analysis of the kinematically redundant mechanisms is described. Then, based on local optimization suitable for real-time control, a general, simple, and effective redundancy resolution algorithm for the mechanisms is developed. Here, the cost function in the optimization is designed to avoid the most problematic singularity configurations, where the end-effector can be locally moved even though all actuated joints are locked. The kinematically redundant mechanisms are shown to effectively avoid singularities and correspondingly increase the singularity-free workspace.

Kinematic Redundancy Resolution for Serial-Parallel Manipulators via Local Optimization Including Joint Constraints

Abstract This paper presents a method for kinematic redundancy resolution for serial-parallel manipulators using local optimization. The local optimization method is computationally efficient and thus suitable for real-time application. Furthermore, the developed method allows for incorporation of both active and passive joint limits. Accordingly, only feasible trajectory solutions are obtained. The method includes a rule-based, heuristic algorithm to provide smooth transitions between unconstrained and constrained motions. Details of the new algorithm are provided and the efficacy of the approach is established through simulation. Additionally, the algorithm is validated by comparison to a widely accepted global optimization method.