High Performance Motion Control Systems Research Articles

Robust fuzzy – backstepping mode control of an induction motor

This paper presents a novel control for induction motors using backstepping control and fuzzy logic. The Backstepping control is suggested as a substitute for the conventional PI controller to attain high-performance motion control systems for the speed, flux, and current control loops. Stability analysis, based on Lyapunov theory, is also conducted to guarantee the convergence of the speed tracking error from all possible initial conditions. The speed regulator was changed to a fuzzy logic regulator. The simulation results confirm that the proposed hybrid control fuzzy-backstepping scheme offers improved performance in terms of trajectory tracking ability and robustness against variation when subjected to time-varying reference input.

Model-based Reinforcement Learning for Ship Path Following with Disturbances

Modelling and control of ships is a challenging task due to their intrinsic nonlinearities and high uncertainty. In the complex and dynamic sea environment, the efficacy of well-designed motion controllers diminishes significantly. To achieve optimal performance, high-performance motion control systems must possess the ability to adapt to diverse working conditions, repel external disturbances, and incorporate learning capabilities. In addressing critical computational challenges encountered in the real-world deployment of autonomous driving agents, Reinforcement Learning (RL) methods have been effectively employed. This paper proposed a reinforcement learning control method for ship path following based on an environmental disturbance model. RL is utilized to learn the dynamic properties of the system to resist environmental disturbances. Experimental results show that the method can follow the path with acceptable accuracy and high robustness.

Synchronization of Electrical Drives via EtherCAT Fieldbus Communication Modules

Synchronization between devices (in particular drive systems) is paramount for multi-axis motion control systems used in Computerized Numerical Control (CNC) machines, robots, and specialized technology machines used in many areas of the manufacturing industry. EtherCAT is an Ethernet-based network that is one of the most popular industrial networks for multi-axis motion control systems. EtherCAT is standardized in the IEC 61158 and IEC 61784 standards. In the article, an EtherCAT communication network for electrical drives is presented. The article focuses on the synchronization in the EtherCAT network consisting of one master device and slave servo drive devices. Special attention is given to synchronization mechanisms in EtherCAT, such as distributed clocks in slave servo drives devices. For this purpose, a laboratory stand was built consisting of two prototype servo drive devices with BLDC motors equipped with EtherCAT communication modules. A description of the working developed EtherCAT communication modules is given. Authors in communication modules ware used an EtherCAT Slave Controller (ESC) chip (AX58100) to implement lower EtherCAT layers. EtherCAT application layer was implemented in software form on a 32-bit microcontroller, based on CANopen over EtherCAT (CoE) CAN in Automation 402 (CiA402) profile. This research’s main contribution was to show the time dependencies regarding synchronization in terms of data flow in the EtherCAT communication stack in slave servo drive devices. The research results showed that the synchronous operation of drives is mainly influenced not by the mechanism of distributed clocks that ensures synchronization in the EtherCAT network but the implementation of the highest layer of the communication stack in slave servo drive devices. Experimental results are presented that prove the modules’ adequacy for use in high-performance motion control systems.

A universal digital motion controller design for servo positioning mechanisms in industrial manufacturing

• A universal digital motion controller design with theoretical analysis is presented. • The controller uses a synergy of linear and nonlinear control with disturbance rejection, and achieves desirable performance. • The controller is fully parameterized, with the advantage of fast implementation and convenience of on‐line tuning. • The controller has the potential of integration with an identification algorithm to form a self‐tuning motion control system. • The design was verified on a DSP-controlled testbed, and demonstrated a competitive performance against the popular ADRC. A parameterized design of universal motion controller is proposed in discrete-time domain using composite nonlinear control approach for high-performance servo mechanisms in industrial automation. First, the model of servo mechanisms is converted into discrete-time state-space form, and a linear control law is designed, consisting of state feedback, reference feed-forward and disturbance compensation. Next, a nonlinear control law is constructed to smoothly modulate the closed-loop damping as the system output approaches the reference. To estimate the unmeasurable velocity and disturbance, a reduced-order extended-state observer is adopted. The final controller is a combination of the above three parts and is fully parameterized in some fundamental tuning parameters. The controller was applied to a permanent magnet synchronous motor (PMSM) drive, which usually serves as the actuator for high-performance motion control systems. After MATLAB simulation, experimental test using a digital signal processing board was conducted, to verify the effectiveness of the proposed design.

Advanced Motion Control for Next-Generation Industrial Applications

In this special section, a total of ten papers are included, covering a variety of aspects of advanced motion control for industrial applications. The first two papers are on the control of the robotic elastic joint. The classical two-degrees-of-freedom robot control is extended by the virtual torsion sensor in the loop. The proposed control is experimentally evaluated on a single-joint robot consisting of an actuator with harmonic-drive gear and inertial load under additional impact of gravity. Also proposed is an acceleration-based robust controller for the position and force control problems of a novel variable stiffness series elastic actuator (SEA). The vibration of the novel SEA and external disturbances are suppressed by using the resonance ratio control and arm disturbance observer, respectively. The intrinsically safe mechanical structure and high performance motion control system provide several benefits in industrial applications.

An Acceleration-Based Robust Motion Controller Design for a Novel Series Elastic Actuator

This paper proposes an acceleration-based robust controller for the motion control problem, i.e., position and force control problems, of a novel series elastic actuator (SEA). A variable stiffness SEA is designed by using soft and hard springs in series so as to relax the fundamental performance limitation of conventional SEAs. Although the proposed SEA intrinsically has several superiorities in force control, its motion control problem, especially position control problem, is harder than conventional stiff and SEAs due to its special mechanical structure. It is shown that the performance of the novel SEA is limited when conventional motion control methods are used. The performance of the steady-state response is significantly improved by using disturbance observer (DOb), i.e., improving the robustness; however, it degrades the transient response by increasing the vibration at tip point. The vibration of the novel SEA and external disturbances are suppressed by using resonance ratio control (RRC) and arm DOb, respectively. The proposed method can be used in the motion control problem of conventional SEAs as well. The intrinsically safe mechanical structure and high-performance motion control system provide several benefits in industrial applications, e.g., robots can perform dexterous and versatile industrial tasks alongside people in a factory setting. The experimental results show viability of the proposals.

Implementation of Fuzzy Self-Tuning PID and Feed-Forward Design for High-Performance Motion Control System

The existing conventional motion controller does not perform well in the presence of nonlinear properties, uncertain factors, and servo lag phenomena of industrial actuators. Hence, a feasible and effective fuzzy self-tuning proportional integral derivative (PID) and feed-forward control scheme is introduced to overcome these problems. In this design, a fuzzy tuner is used to tune the PID parameters resulting in the rejection of the disturbance, which achieves better performance. Then, both velocity and acceleration feed-forward units are added to considerably reduce the tracking error due to servo lag. To verify the capability and effectiveness of the proposed control scheme, the hardware configuration includes digital signal processing (DSP) which plays the main role, dual-port RAM (DPRAM) to guarantee rapid and reliable communication with the host, field-programmable gate array (FPGA) to handle the task of the address decoder and receive the feed-back encoder signal, and several peripheral logic circuits. The results from the experiments show that the proposed motion controller has a smooth profile, with high tracking precision and real-time performance, which are applicable in various manufacturing fields.

Sensing and Control of Friction in Positioning

Robust sensing and control in fine positioning is a key technology in the presence of various disturbances. For example, the position accuracy of high performance motion control systems is adversely affected by vibrations due to compliance and nonlinear effects such as friction. This paper focuses on a robust friction sensingmethodology based on the sensor fusion via the neural network from AE (acoustic emission) sensors and the feedforward control for the compensation of friction. This compensation is found to be useful for positioning control when frictions applied to the system are adequately and robustly estimated. Encouraging transient response and steady-state control performance were observed in the experimental results of positioning control of a one-dimensional transmission mechanism. The proposed friction sensing and feedforward control can be applied without modifications for nanoscale positioning.

Laser Pointing and Tracking Using a Completely Electromagnetically Suspended Precision Actuator

S TABLE and precise laser beam positioning is required for reliable laser communications among satellites. A very small angular movement of the source laser corresponds to a significant beamposition errorwhen amplified by the large distance between the transmitting and receiving stations and can thus throw a laser beam far off target. The desired pointing and tracking accuracy is typically on the order of 1 rad rms [1,2]. Many efforts have been taken to improve performances of the pointing and tracking systems for intersatellite optical links. A Stewart platform demonstrated a 1 rad rms pointing error in the ambient laboratory disturbance environment [3]. Passive vibration isolation techniques are usually adopted to reduce adverse effects of vibrations on the precision pointing performance objectives [4]. Magnetic levitation technology has been used in high performance motion control systems, owing to its noncontact nature, active control ability, and feasible multiple degree-of-freedom (DOF) actuation. A 6-DOF hybrid magnetic/fluidic positioning stage achieved a 0.3 nm resolution within a 100 m cube [5]. A 6-DOF magnetically levitated device covered a 300 m travel range in translation and 3.5 mrad in rotation with a 2 nm accuracy in translation and 300 nrad in rotation, and a 5 nm resolution [6]. But these systems require many actuators that add difficulties in controls. Very limited stroke is another major barrier [7]. Magnetic bearings are advantageous in special environments with vacuum or extreme temperature, where lubrication problems associatedwithmechanical bearings cannot be ignored. Self-bearing motors (SBMs) combine magnetic bearing and electric motoring functions into a single electromagnetic actuator to perform both force and torque production, and are attractive to space applications where room and weight are also of great concerns. One particular permanent magnet (PM) SBM design featuring a slotless stator allows for a smoother torque generation and is considered to be a good candidate to solve space-borne precision pointing and tracking problems [8]. To investigate its potential of improving pointing accuracy within a large range, two such slotless PM SBMs were incorporated into a 6-DOF magnetic actuator. Reference [9] showed that six decoupled proportional-integral-derivative (PID) controllers achieved stable levitation and smooth angular slewing of the 6-axis active actuator as a positioning stage, using a tape encoder system as the pointing sensor. In this work, the actuator is integrated into a laser pointing and tracking system setup to demonstrate its capability in tracking an external optical pointing sensor through a laser crosslink. The laser acquisition and reacquisition as well as precision pointing and tracking of the system in azimuth are implemented by a switching control strategy between the large-angle encoders and a small-angle laser position sensing detector (PSD) in rotation control, whereas the other five axes remain closed-loop controlled for magnetic bearing stabilization and precision noncontact pointing. Experimental results show that the system achieves high accuracy laser pointing and tracking over a large azimuth range using the single actuator.

An Improvement of Speed Control Performances of a Two-Mass System using a Universal Approximator

A new control scheme using a universal approximator based on a radial basis function network (RBFN) is proposed and investigated for improving the control characteristics of the high-performance motion control system. This control method presents better performance in the corresponding speed vibration response, compared with the inverse model-based disturbance observer. The proposed RBFN-universal approximator keeps the self-learning capability, whereas the inverse model-based disturbance observer with the low-pass filter should adjust the time constant of the filter according to the resonance frequency determined by varying the system parameters. The simulation results show the validity of the proposed control scheme.

MULTIVARIABLE H∞ CONTROLLER DESIGN AND TESTING FOR A 2.4M TELESCOPE

This paper considers high performance motion control systems for the Azimuth axis of a 2.4m Altitude-Azimuth telescope manufactured by Telescope Technologies Limited (TTL). Tracking performance is paramount and the telescope is designed to operate with no surrounding enclosure; wind disturbances that could degrade the tracking performance are a major consideration. Previous robust control designs have used a single-input-single-output (SISO) architecture for position tracking, and this paper will assess the stability and performance of a multi-input-multi-output (MIMO) controller using simulations and test data from the real telescope. Simulations indicate that the MIMO design offers better wind disturbance rejection, and the test data show that the implementation of a MIMO control architecture is feasible.

DSP-based robust control of an AC induction servo drive for motion control

A design method based on the internal model control (IMC) theory has been developed for the robust control of a low-power AC induction servo drive in application of high-performance motion control systems. Indirect vector control with software current control technique has been developed to achieve fast response decoupling control of the induction motor. An equivalent model representing the control dynamics of the decoupled AC induction motor is used for the analysis and synthesis of the IMC controller. To improve the control performance of the servo drive with given frequency-domain robustness specifications, a design procedure for the servo controller is developed based on the IMC theory. The proposed control scheme has been realized using the Texas Instruments TMS320C14 single-chip digital signal processor. Experimental results are given to verify the proposed design method.

Real-time issues of transputers in high-performance motion control systems

The real-time issues related to using transputers to implement high-performance AC motor drive controllers because of their direct support for parallel processing are addressed. They include event response time, scheduling strategies, I/O, and real-time kernel performance. The implementation of part of a real-time kernal consisting of a multiple event handler and an efficient scheduler, to improve the transputer's real-time performance, is described. In addition to supporting high-performance controller tasks, the real-time kernel implements features such as parameter sampling and user interaction. The kernel is intended to be a platform to support a highly programmable and configurable controller suitable for a wide range of motion control applications. Test results are presented to show the performance of the kernel. >