Study of Force Feedback Control Based on Positioning Information of Elastic Support Mechanism

In this paper, model-based precision force and position control of an ionic polymer metal composite (IPMC) is presented. A 23.8 mm × 3.4 mm × 0.16 mm IPMC strip was used as an actuator in a cantilever configuration. Open-loop force and position responses of an IPMC are not repeatable, and hence closed-loop precision control is of critical importance to ensure proper functioning, repeat-ability and reliability. After feedback controllers were designed and implemented with empirically obtained fourth-order plant transfer functions, the overshoot decreased from 460 to 2.8 per cent and the settling time was reduced from 37.5 to 3.22 s in force control. In position control the overshoot decreased from 333 to 20.3 per cent and the settling time was reduced from 21.5 to 2.56 s. Microscale precision force and position control capabilities of the IPMC actuator were also demonstrated experimentally. An 8 μN force resolution was achieved with a force noise of 0.5μN r.m.s., and the position resolution was 6 μm with a position noise of 2.5 μm r.m.s. The maximum force and tip displacement achieved with the IPMC actuator under closed-loop control were 2 mN and 5 mm respectively. The IPMC actuator could follow various commanded force and position trajectories such as sinusoidal and trapezoidal position profiles, and a velocity profile with a 3 mm/s maximum velocity. A novel hybrid force and position control strategy demonstrated its utility in practical micromanipulalion applications where the actuator force must be limited to prevent damaging micro-objects. High-precision control of the IPMC at low force level proved its potential for micromanufacturing and micromanipulation applications such as robotic and biomedical microgrippers.

Model-based precision position and force control of SMA actuators with a clamping application

The increasing demand on the optical performance of micro-aspheric glass lenses used for consumer, medical, as well as industrial applications places a high requirement on the surface quality of the molds used for replicating these lenses. However, it is difficult, almost impossible to generate a supersmooth surface with extremely high form accuracy by using the current cutting or grinding techniques. Therefore, this paper presents a corrective polishing process to finish micro-aspheric molds made of tungsten carbide by applying the vibration-assisted polishing method, aiming to obtain tens-of-nanometer form accuracy and subnanometer surface roughness. A polishing system which provides precise position, angle, and force control in 5 degrees of freedom (DOF)is employed for the experiments, and a tilting angle control method is introduced for the ease of the precisely controlling polishing force so as to keep the material removal rate stable. Then a dwell time algorithm is proposed by considering the scanning path of the polishing tool and the tilting angle of the workpiece. The experimental results show that after corrective polishing, the form accuracy of a micro-aspheric mold with high numerical aperture (NA) is successfully improved from 230nm peak-to-valley (PV) to under 50nm PV, while the surface roughness is reduced from 7.2nm root-mean-square (rms) to 0.5nm rms.

Precise force control and position control is essential for many robotic applications. During unilateral or bilateral object handling remote applications, human operators apply excess forces on the actuators with the intention of better grip and it is possible to damage the handled objects. This paper proposes position control and force control techniques when human applies excess force. The controllers consist of predefined force and equilibrium position which are correspond to remote environmental object safety. The operator applied excess force is modeled as a spring force through a virtual stiffness model. The paper introduces proportional derivative position control loop to conventional virtual stiffness controller. The force control loop and the position control loop references are combined in the common dimension of acceleration to produce current reference to the actuator. The sensorless sensing techniques of disturbance observer and reaction force observer are utilized to disturbance suppression and external force estimation. In the force controller, estimated reaction force is reduced to desired value by introducing virtual force loop between reaction force observer output and reaction force feedback input. The position control is achieved by introducing a scaling factor to reaction force feedback path. The switching between force control and position control is possible with scaling factor value. The performances of proposed methods are compared with conventional method and validity of the proposed methods is verified by simulations and experiments.

When naval vessels moving on the sea, the carrier air wake disturbance will arise. The carrier air wake makes the landing environment of carrier aircraft fair adverse, which puts forward a high demand for the high precise attitude control of carrier based aircrafts. In this paper, high precise robust attitude control problems for carrier based aircrafts with the carrier air wake disturbance are investigated. Firstly, the small disturbance linearization method is introduced to transform the nonlinear system into a linear one, which is a necessary procedure for aircraft system analysis and controller design. Secondly, the model of the carrier air wake disturbance is established and its effects on the aerodynamic parameters are analyzed in detail. Then the effects are transformed into the augmented disturbance in the system. Thirdly, a nonlinear extended state observer is utilized to estimate the disturbance. Besides, a robust adaptive attitude controller with integral term is proposed to achieve high precision attitude tracking. The stability of the closed-loop system is prove based on Lyapunov theory. Finally, a numerical example is provided to demonstrate the effectiveness of the obtained results.

In modern times, the design and optimization of different actuator systems for controlling a high-precision position control system represent a popular interdisciplinary research area. Initially, only single-stage actuator systems were used to control most of the motion control applications. Currently, dual-stage actuation systems are widely applied to high-precision position control systems such as hard disk drive (HDD) servo systems. In the dual-stage system, a voice coil motor (VCM) actuator is used as the primary stage and a piezoelectric micro-actuator is applied as the secondary stage. However, a dual-stage control architecture does not show significant performance improvements to achieve the next-generation high-capacity HDD servo system. Research continues on how to fabricate a tertiary actuator for a triple-stage HDD servo system. A thermal positioning controller (TPC) actuator is considered promising as the tertiary stage. The triple-stage system aims to achieve greater bandwidth, track density, and disk speed, with minimum sensitivity and greater error minimization. In this work, these three actuation systems with different combinations of proportional plus integral (PI), proportional plus derivative (PD), and proportional plus integral plus derivative (PID) controller, lag-lead controller, lag filter, and inverse lead plus a PI controller were designed and analyzed through simulation to achieve high-precision positioning. The comparative analyses were done on the MATLAB/Simulink simulation platform.

To address the demands for precision and load-bearing capacity in the installation of building panels, a hybrid force-position driven robot with redundant actuation has been developed. The mechanical performance of this robot is primarily governed by its central parallel mechanism, which is equipped with redundant actuators matching the degrees of freedom. Non-redundant and redundant actuators are respectively responsible for position and force control. The inclusion of redundant force-driven joints has increased the internal coupling within the mechanism. To enhance the coordination between position and force control, a hybrid synchronized control method based on cross-coupling has been proposed. Initially, kinematic and dynamic models of the parallel structure were established. Under predefined trajectories, the theoretical inputs for each actuator were calculated using inverse kinematics and dynamics. Subsequently, employing the principle of cross-coupling, the torque output from the position actuators was used as feedback. This feedback was processed by a synchronized coordination controller to adjust the output force of the redundant force-driven joints. By adjusting the output force of the redundant actuators, the torque burden on the position actuators was effectively reduced, thereby enhancing the precision of position control. Additionally, under the same load conditions, smaller power actuators could be utilized for position control, reducing the overall weight of the robot and improving its load-to-weight ratio. To validate the effectiveness of the proposed control strategy, a robotic simulation environment was established. The simulation results demonstrated significant reductions in the average torque required by the position actuators across three different trajectories, with reductions of 91.43%, 54.56%, and 80.6% respectively. Finally, the load-bearing capacity and the load-to-weight ratio of the prototype were assessed. Experimental results confirmed that the prototype achieved a load-to-weight ratio of 15.83%, validating the effectiveness of the hybrid synchronized control method based on cross-coupling.

Thickness measurements using an ultrasonic contact test is a well-known nondestructive evaluation technique. However, its implementation in a robotic system with a closed-loop feedback control for artificial intelligent measurements requires precise information of positioning and force of the ultrasonic probe. In this work, we describe an ultrasonic probe developed in our lab that uses a semispherical soft membrane made from an elastomer. The aim is to develop a methodology for precise positioning and force control of a dry contact ultrasonic probe based on the ultrasonic signal information processed using sparse matrix optimization and Fourier analysis techniques. The results show that the proposed methodology makes easy to achieve a fine tuning of the probe orientation with high sensitivity to load and misalignment in order to perform accurate thickness measurements.

This paper investigates the problem of the position control in switched reluctance motor drives. Advanced proportional-integral (PI) and proportional-differential (PD) controllers for the speed and position control, respectively, are adopted. The parameters of the controllers are on-line fine tuned according to the load torque and rotor speed, for providing high dynamic performance and precise position control. In order to improve the set-point tracking of the drive performance, a low-pass filter is included in the position controller. The proposed four-quadrant control scheme is based on the average torque control method. The turn-on and turnoff angles are on-line determined through simple formulas and the proposed fine tuning regulator is capable of maintaining the torque ripple at an acceptable level over a wide speed range. This is important since the position precision is highly influenced from the motor torque ripple. Experimental results of the switched reluctance motor dynamic response are presented to verify the theoretical considerations and to demonstrate the effectiveness of the proposed control scheme.

Time delay compensation is very important in the teleoperation field because time delay deteriorates the system performance and stability. Therefore, a lot of research about time delay compensation have been proposed and developed. One of the effective methods, communication disturbance observer (CDOB) has realized the time delay compensation for the position tracking in bilateral teleoperation. Thanks to CDOB, the smooth operation has been achieved. However, the precise force matching has not been achieved yet by any methods. To solve this problem, the time delay compensation method for the force control system has been proposed. This method realizes the precise contact force control under time delay. Therefore, the time delay compensation method is extended to bilateral teleoperation in this paper. In other words, the time delay compensation for the force controller in the bilateral teleoperation system is proposed toward the precise force matching. The validity is confirmed by the experiments.

The typical advantages of electric propulsion are known for long and and an increasing number of spacecrafts is equipped with EP for North-South-Station Keeping, orbit transfer or as primary propulsion system in case of interplanetary probes. An new and emerging field is the high precision positioning and orbit control of spacecrafts. Especially formation flying benefits from the high accuracy in thrust of EP systems. Challenging missions and their demands for the propulsion system are described. The description highlights the need of miniaturised electric propulsion systems. Amoung all the different EP concepts, radiofrequency ion thrusters show excellent scalability,also for down scaling. Astrium, University of Giesen and their partners have been working in the field of radio-frequency propulsion technology for long. Their approach, bases on a flight proven technology is presented. The basic principle is explained together with the technology's heritage. Test results complete the publication.

Precise positioning and precise force control requirement in haptic devices necessitate the kinematic calibration of the device. Since force control algorithms in haptic interfaces employ Jacobian matrix which includes kinematic model parameters, kinematic calibration is not only important for pose accuracy but also for force control. The deviation of kinematic parameters and joint transmission errors are main reasons disturbing the kinematic calibration of the manipulators. In haptic device design, capstan drives and parallelogram mechanisms are preferred to use for actuation. Hence, their transmission errors should be estimated in the kinematic calibration. This paper presents a simulation study including the estimation of the kinematic parameters and transmission errors due to the capstan drives and parallelogram mechanism for a 7 DOF haptic device. The closed chain kinematic model is preferred to use for easy implementation in the presented kinematic calibration study.

Precise position force control is the core and difficulty of robot technology, especially for robots with redundant degrees of freedom. For example, track-based controls often fail to grind the robot due to the intolerable impact force applied to the end-effector. The main difficulties lie in the coupling of motion and contact forces, redundancy analysis and physical constraints. In this chapter, we propose a new motion force control strategy under the framework of recursive neural network. The tracking error and contact force are described respectively in the orthogonal space. By choosing the minimum joint torque as the secondary task, the control problem is transformed into the QP problem under multi-constraint conditions. In order to obtain real-time optimization of the joint torque relative to the non-convex joint angle, the original QP is reconstructed at the velocity level, and the original objective function is replaced by the time derivative. Then a convergent dynamic neural network is established to solve the improved QP problem online. The robot position control based on recursive neural network is extended to the robot position control based on position force, which opens a new way for the robot to turn from simple control angle to crossover design with convergence and optimality. Numerical results show that the proposed method can realize precise position force control, deal with inequality constraints such as joint angular velocity and torque limitation, and reduce joint torque consumption by 16% on average.

Electric load simulator (ELS) systems are employed for electric power steering (EPS) test benches to load rack force by precise control. Precise ELS control is strongly influenced by nonlinear factors. When the steering motor rapidly rotates, extra force is directly superimposed on the original static loading error, which becomes one of the main sources of the final error. It is key to achieve ELS precise loading control for the entire EPS test bench. Therefore, a three-part compound control algorithm is proposed to improve the loading accuracy. First, a fuzzy proportional–integral plus feedforward controller with force feedback is presented. Second, a friction compensation algorithm is established to reduce the influence of friction. Then, the relationships between each quantity and the extra force are analyzed when the steering motor rapidly rotates, and a net torque feedforward compensation algorithm is proposed to eliminate the extra force. The compound control algorithm was verified through simulations and experiments. The results show that the tracking performance of the compound control algorithm satisfies the demands of engineering practice, and the extra force in the ELS system can be suppressed by the net torque corresponding to the actuator’s acceleration.

In this paper, a simplified mathematical model of a telescope system is established, and a linear active disturbance rejection controller (ADRC) is implemented in high precision position and velocity control of a telescope servo system. The internal mechanical resonance and some nonlinearity in the tracking system, in addition to external disturbances of uncertain characteristics are collectively treated as a generic disturbance, and this total disturbance is estimated by a proposed linear extended state observer. This total disturbance is then rejected by disturbance compensation. The control algorithm employs only three parameters, which makes the controller very easy to tune. Experimental results are presented to demonstrate the good performance of the proposed telescope tracking method.