Setpoint Position Control Research Articles

Rolling Contact Motion Generation and Control of Robotic Fingers

Dexterity in human hand is connected with the fingertip rolling ability. In this work we consider rolling motion of spherical robotic fingertips as one of the control objectives together with the set point position control and force trajectory tracking. The generation of a rolling motion trajectory is proposed and a control solution is designed which achieves prescribed transient and steady state tracking behavior. The proposed control law is structurally and computationally simple and does not utilize the dynamics of the robot model or its approximation. A simulation of a five degrees of freedom robot show excellent contact rolling performance even at cases of adverse friction conditions while alternative controllers lead to contact sliding. Experiments with a KUKA LWR4 + are performed to validate the proposed method.

Anti-windup Controller Design for Anthropoid Robot Manipulators with Actuator Saturations

A static anti-integrator-windup controller design method is proposed for anthropoid robot manipulators. The asymptotic stability is achieved using a simple static anti-windup gain matrix for set point position control with PI or PID controllers. The control performance is verified on a two-link robot arm with a gravity term by numerical simulations and experiments.

Two-Dimensional Input Shaping for One-Dimensional Continua

This paper extends input shaping control to one-dimensional continua. Unlike discrete systems where the input is shaped only in the temporal domain, temporal and spatial input shaping can produce zero residual vibration in setpoint position control of distributed strings and beams. For collocated and noncollocated boundary control of strings and domain control of strings and pinned beams, the response to step inputs is solved in closed form using delays. For a clamped beam model, a closed form infinite modal series is used. The boundary controlled string can be setpoint regulated using two-pulse zero vibration (ZV) and three-pulse zero vibration and derivative (ZVD) shapers but ZVD is not more robust to parameter variations than ZV, a unique characteristic of second-order partial differential equations systems. Noncollocated ZV and ZVD boundary control enables rigid body translation of a string with zero residual vibration. Domain controlled strings and pinned beams with spatial input distributions that satisfy certain orthogonality conditions (e.g., midspan point load or uniformly distributed load) can be setpoint regulated with shaped inputs. For the cantilevered beam, modal shaping of the input distribution and ZV or ZVD temporal shaping drives the tip to the desired position with zero residual vibration.

A Model-Free Cross-Coupled Control for Position Synchronization of Multi-Axis Motions: Theory and Experiments

In this brief, a model-free cross-coupled controller is proposed for position synchronization of multi-axis motions. The position synchronization error of each axis is defined as the differential position error between this axis and its two adjacent axes, which is then coupled with the position error to form a coupled position error. A proportional and derivative (PD)-type synchronization controller with feedback of this coupled position error is proposed and proven to guarantee asymptotic convergence to zero of both position and synchronization errors in a setpoint position control. A setpoint tracking controller is further developed by adding feedforward control terms and a saturation function to the PD synchronization controller. The proposed method is easy to implement in practice since it is model free and the control gains are time-invariant. Experiments are performed to verify effectiveness of the proposed approach

Integration of saturated PI synchronous control and PD feedback for control of parallel manipulators

High-precision motion of parallel manipulators depends not only on the position accuracy of each actuator, but also on the position synchronization of all actuators. This paper presents a simple synchronized control algorithm for the setpoint position control of parallel manipulators, by incorporating cross-coupling technology into a common proportional-derivative (PD) control architecture. An integrated controller is developed, consisting of a PD control and a saturated proportional-integral (S-PI) control with feedback of the differential position errors amongst actuators (defined as the synchronization errors). The controller can stabilize the motion of each actuator, and meanwhile synchronize all actuators' motions so that both position and synchronization errors converge to zero. The control algorithm does not use the modeling parameters in the controller formulation, and thus permits easy implementation in practice. It is proved that the proposed method can guarantee global asymptotical stability of the system. Experiments conducted on a planar three-degree-of-freedom parallel manipulator demonstrate the effectiveness of the proposed approach.

Position and force tracking of a two‐manipulator system manipulating a flexible beam

AbstractThis article discusses the issue of hybrid position and force control of a two‐manipulator system manipulating a flexible beam in trajectory tracking. Unlike our previous approach of set‐point position control in the trajectory tracking, the system coordinates are hard to be regulated to the desired states with nonzero tracking velocities under continuous feedback control. In this study, we design a hybrid position and force tracking controller while using saturation control to compensate for the effect of beam vibration dynamics on the tracking performance. All parameters and states used in the controller are readily available so that the proposed method is feasible to implement. Under the proposed controller, the tracking error asymptotically converges to a predetermined boundary. Simulation results demonstrate the validity of the proposed approach. © 2001 John Wiley & Sons, Inc.

Parameter Identification of Gravity and Friction Forces for Nonlinear Mechanical Systems

Abstract Dynamics of a nonlinear mechanical system under static and Coulomb frictions are shown to be equivalent to a nonlinear position-dependent circuit including a set of on-off switches and analyzed as a VSS(Variable Structure System). In particular, in the case of robot dynamics under the existence of static and Coulomb frictions at each joint, an ordinary PD feedback for setpoint position control with gravity compensation leads to a trapping of motion at some immovable state within a finite time without reaching the given target position. On the contrary, by introducing regressors for uncertain parameters of gravity forces and viscous, static, and Coulomb frictios it is possible to show that a proper update law of such regressors together with an appropriate PD feedback makes the closed-loop robot system globally asymptotically stable without incurring any offset. These results suggest a proposal of inertia-only robots, or gravity/friction-free robot. It is further claimed that such a gravity/friction-free robot can be regarded as a starting-point testbed for further implementation of impedance or compliant control towards realization of human-friendly robots.

H∞ Optimal Tuning of the Saturated PID Controller for Robot Arms Using the Passivity and Dissipativity

A modified PID controller which feeds a saturated position error feeedback instead of proportional one guarantees the global asymptotic stability for setpoint position control. For this controller, this paper proposes an H∞ tuning method to realize the disturbance attenuation against unknown torque disturbances at each joint. In its stability analysis, the following facts are shown, 1)global asymptotic stability of the closed loop system and disturbance attenuation are feasible easily by taking account of physical properties of robot dynamics 2)disturbance attenuation with arbitrary gain can be established independently of the asymptotic stability. 3)as to robot dynamics, the storage function should be taken as a total internal energy and if the total internal energy is chosen as the storage function, the robot system has the KYP property which connects the passivity concept and dissipativity concept.