Servo Tuning Research Articles

Intelligent Servo Tuning of High-Speed Machine Tools Using Circular Test

PID control and multi-loop control schemes are widely used in machine-tool computer numerical control servo systems. However, fast and efficient tuning methods for solving mismatches are uncommon. Servo mismatch is an important source of error owing to its effect on positioning accuracy. A circular test using a double ball-bar is used to access such errors. This study proposed a simple, model-free, and inexpensive approach without add-on measurement to solve the servo mismatch system by measurement of simultaneous movements in two axes. Based on the proposed features, our approach is established by iterative tuning using Lagrange interpolation polynomials for the position and velocity loops parameters. The system performance can be improved to iteratively minimize the mismatch of servo systems by tuning the servo parameters of multi-axis feed drive systems. The proposed approach is based on the linear scale signals of iterative circular tests, which avoids using expensive measurement instruments. The experimental results demonstrate the accuracy of feed drive system diagnosis and the performance improvement (mismatch is improved from 0.67 to 0.01ms).

Long term temperature stability of thermal cycler developed using low profile microprocessor cooler

<span lang="EN-US">Developing a low-cost thermal cycler for a polymerase chain reaction (PCR) is becoming interested in the pandemic era caused by viruses. PCR is the standard gold for the diagnostic. However, in a low-income country, the availability of the device is limited. In this work, the development of a thermal cycler uses electronic modules available in the market. The central part is thermoelectric for heating and cooling, an embedded system to control, and a low-profile cooling fan. The system temperature control used a combination of feedforward, bang-bang, and proportional-integral-derivative (PID) control. The control parameter of the PID was successfully obtained by using Chien servo tuning. The feedforward and bang-bang control are used to optimize the cooling cycle and minimize the rise time. The system shows a well-suited temperature accuracy at the denaturation, annealing, and extension temperature with a temperature deviation of less than 0.5 °C. System performance is maintained even though the system has been running non-stop for 24 hours. The low-profile cooling fan, which is usually used for CPU cooling, shows good results in maintaining temperature stability.</span>

A generic method for servo tuning based on dynamic modeling and task description

In robotics or machining, task quality is strongly linked to servo tuning. Indeed, geometrical and dynamic behavior of the mechanical structure could be degraded when a coarse tuning is achieved. Several P/PI or PID tuning methods can be used but generally uncorrelated with industrial context or mechanical considerations. In this paper, we propose a generic tuning method based on dynamic modeling of the mechanical structure and model parameters experimental identification. Therefore, the proposed tuning is adapted to the real dynamic behavior of the mechanical structure under task load while being sufficiently simple to be implemented in an industrial context. The method is illustrated on a vertical axis.

Remote Servo Tuning System for Multi-Axis CNC Machine Tools Using a Virtual Machine Tool Approach

Servo systems affect the performances of machining in accuracy and surface quality for high speed and precision machine tools. This study introduces an efficient servo tuning technique for Computer Numerical Control (CNC) feed drive systems using particle swarm optimization (PSO) algorithm by virtual machine tool approach. The proposed approach contained a system identification phase and a servo tuning phase based on the same bandwidth for all axes feed drive systems. The PSO algorithm was adopted to obtain the system parameters and maximize the corresponding bandwidth. An efficient two-step servo tuning method based on gain and phase margins was proposed for high speed and precision requirements. All feed drive systems controller gains were optimized simultaneously for synchronization. A remote system called Machine Dr. was established for servo tuning and monitoring. Simulation and experimental results were introduced to illustrate the effectiveness of the proposed approach.

Inertia Identification and PI Parameter Tuning of PMSM Servo Drives

The goal of this paper is to improve the performance of permanent magnet synchronous motor(PMSM) servo system by identification of the inertia parameter and auto-tuning of PI parameters. The method relies on the speed acceleration and deceleration response produced by speed ramp signals applied to a speed-controlled servo. The proposed method relies on simple numerical calculations, thus make the proposed scheme more practical. After the knowledge of the inertia parameter, the tuning of the speed control loop can be performed. The experimental results verified that the proposed identification scheme can estimate inertia parameters accurately and effectively and the control system tuned can achieve good dynamic performance.

機械学習の枠組みに基づく能動型探索アルゴリズムのサーボパラメータ調整問題への適用性の検討

機械学習の枠組みに基づく能動型探索アルゴリズムのサーボパラメータ調整問題への適用性の検討

615 ダイレクトドライブモータを採用した工作機械の旋回軸における角加速度オートサーボチューニングの効果(GS11,13 工作機械制御,研究討論セッション)

615 ダイレクトドライブモータを採用した工作機械の旋回軸における角加速度オートサーボチューニングの効果(GS11,13 工作機械制御,研究討論セッション)

Research of an Open CNC System of Machine Tool for Finding and Repairing Surface Damage on KDP Crystal

In order to find and repair surface damage on KDP crystal, an open computer numerical control(CNC) system has been developed. This paper introduces the hardware structure of the control system, explains the development of an open CNC system software, which has friendly human-machine interface (HMI) and can make the finding and repairing process efficiently and conveniently and also expounds the algorithm and related parameters for servo tuning. With the open CNC system, the process of finding surface damage is accomplished in 3 hours and clear images of crystal surface damage is taken by CCD. And also, with the help of the open CNC system, a 600µm-diameter, 25µm-depth Gaussian repair contour with low roughness is obtained. Experimental results prove that the open CNC system for finding and repairing surface damage on KDP crystal meets the requirement of efficient detection and ultra-precision machining.

Modeling and improvement of dynamic contour errors for five-axis machine tools under synchronous measuring paths

In this paper, a contour error model of the tool center point (TCP) for a five-axis machine tool is proposed to estimate dynamic contour errors on three types of measuring paths. A servo tuning approach to achieve five-axis dynamic matching is utilized to improve contouring performance of the cutting trajectory. The TCP control function is developed to generate measuring trajectories where five axes are controlled simultaneously to keep the TCP at a fixed point. The interpolation method of the rotary axes with S-shape acceleration/deceleration (ACC/DEC) is applied to plan smooth five-axis velocity profiles. The contour error model for five axes is derived by substituting five-axis motion commands into servo dynamics models. The steady state contour error (SSCE) model is demonstrated to illustrate three particular dynamic behaviors: the single-circle with amplitude modulation, double-circle effect and offset behavior. Furthermore, the model is also utilized to investigate the behaviors of dynamic contour errors change in 3D space. The factors that affect dynamic contour errors, including the initial setup position, feedrate and five-axis servo gains, are analyzed. With the developed servo tuning process under the measuring paths (CK1, CK2 and CK4), the contour errors caused by servo mismatch are reduced remarkably. Finally, experiments are conducted on a desktop five-axis engraving machine to verify the proposed methodology can improve dynamic contouring accuracy of the TCP significantly.

Servo and Regulation Tuning of PID Control Using <i>M<sub>s</sub></i>-based Robustness

Servo and Regulation Tuning of PID Control Using <i>M<sub>s</sub></i>-based Robustness

An Approach to Motion Control Applications Based on Advanced Programmable Devices

In this article a methodology for constructing a simple servo loop for motion control applications which is suitable for educational applications is presented. The entire hardware implementation is demonstrated, focusing on a microcontroller-based (μC) servo amplifier and a field programmable gate array-digital signal processor (FPGA-DSP) motion controller. A novel hybrid architecture-based digital stage is featured providing a low-cost servo drive and a high performance controller, which can be used as a basis for an industrial application. Communication between the computer and the controller is exploited in this project in order to perform a simultaneous adaptive servo tuning. The USB protocol has been put into operation in the user front-end because a high speed sampling frequency is required for the PC to acquire position feedback signals. A software interface is developed using educational software, enabling features not only limited to a motion profile but also the supervisory control and data acquisition (SCADA) topology of the system. A classical proportional-integral-derivative controller (PID) is programmed on a DSP in order to ensure a proper tracking of the reference at both low and high speeds in a d.c. motor. Furthermore, certain blocks are embedded on an FPGA. As a result, three of the most important technologies in signal processing are featured, permitting engineering students to understand several concepts covered in theoretical courses.

Feed Drive Simulator

Feed drive systems consisting of servo motors and ball screws are generally used with NC machine tools, wire bonders, tip mounters, etc. Higher speed and accuracy are continuously required to the feed drive systems. In order to achieve higher performance of the systems, it is effective to analyze the dynamic behaviors using simulations. This study proposes a feed drive simulator consists of parameter identification and simulation modules. The parameter identification module consists of 3 sub-modules; identification system for friction forces, identification system for frequency response, and identification system for electric delay. The identification algorithms for unknown parameters are newly proposed. The simulation module is based on a mathematical model which consists of mass, inertias, stiffness, damping, frictions, servo gains, electrical delay, and control frequency. The simulation module also has a servo tuning function. The simulator, which includes a Graphical User Interface (GUI) was developed using Visual C++. Actual feed drive systems were used to confirm the effectiveness of the simulator. It was confirmed that the simulator identifies parameters systematically, simulates physical values for different motions, and automatically determines servo gains based on the parameters identified.

Parameter identification when designing a solid-modeling-based grinding-machine controller

Modern computer-aided design and dynamics simulation tools allow design and testing to be performed in a virtual-reality environment. The integration of controller synthesis programs also makes it possible to perform servo tuning without actually having to build a prototype. However, most servo controllers are based on integer processors for machine tools, and the integer numbers entering into a servo tuning interface often do not directly reflect the magnitudes of the actual controller parameters, impairing the virtual tuning. This study addressed this problem by employing a gain parameter to each control parameter, and developing an identification algorithm for these parameter gains. The identification results were used to tune the servo, which was first carried out within the solid-modeling simulation environment. This procedure makes it easy to implement the controller parameters in the actual machine. The actual implementation of the resultant controller verified that the proposed method improved the servo performance, including eliminating the overshoot in both position and velocity responses of the grinding machine.

A Servo Parameter Tuning Method For HighspeedNC Machine Tools Based On ContouringError Measurement

In the latest high-speed and high-acceleration NC machine tools, the structural vibration is one of the most critical factors to deteriorate the machine’s contouring performance. Particularly on such a machine, the parameters in a CNC servo control system must be carefully tuned, since too high response of the latest CNC units often causes severe structural vibration. This paper presents a practical servo tuning method for high-speed machine tools to optimize its contouring accuracies. In order to reduce the structural vibration with the minimum sacrifice of control bandwidth, the tuning is based on iterative measurement and simulation of the machine’s contouring performance. A case study shows that a proper tuning of servo parameters significantly reduces the structural vibration and improves the machine’s overall contouring accuracy.

工作機械の輪郭精度向上をめざしたＣＮＣパラメータチューニングに関する研究

This paper deals with a practical servo tuning method for high speed and high acceleration feed drives in the latest NC machine tools. CNC-servo systems in machine tool drives generally have current-velocity-position feedback controls, a feedforward controller and a command generator. Techonological progress in hardware and software makes it possible to implement a high response servo control for commercial feed drives. When feed drives are built in a complicated structure, however, vibration problems tend to occur in practical applications. Particularly vibrations at low frequencies deteriorate the contoing accuracy. In order to search the most adequate combination of CNC-servo parameters, a quick and accurate tuning method is required. This paper proposes a systematic tuning method based on simulation and measurement technology. The effectiveness of the proposed tuning method is validated by a case study involving a commercial machining center.

A two-level servo structure with knowledge-based tuning

This paper presents a two-level structure for servo controllers. The lower level is occupied by a conventional servo loop of the proportional-integral-derivative type. The upper level consists of a knowledge-based tuner for the servo parameters. Expert knowledge expressed in the form of linguistic fuzzy rules represents the knowledge base for servo tuning. These rules, along with membership functions for condition and action variables, are processed through fuzzy logic to obtain a multi-dimensional membership function for the knowledge. Tuning inferences are made from the response of the servo loop by applying the compositional rule of inference to the knowledge base. This paper presents a general theory for the development of a knowledge-based tuner. Specifically, the concepts of fuzzy resolution and rule dissociation are introduced. A parallelism between conventional parameter-adaptive control and fuzzy tuning control is pointed out. Through rule dissociation to an elementary level, the fuzzy resolution is arbitrarily improved. By introducing a monotonicity assumption, an analytical framework is established. It is shown that in this framework, fuzzy tuning may be expressed as an algebraic scheme, and consequently the dynamic characteristics such as stability of the overall tuning system may be established purely from the dynamics of the original system. A numerical example is presented to illustrate the basic scheme of fuzzy tuning.

A Knowledge-Based Control Structure for Robotic Manipulators

The proposed control structure has a three-level hierarchy. The lowest level has a set of PID controllers closed around a high-speed decoupling and linearising controller. The second level contains a set of servo experts, one for each degree of freedom of the robot. A servo expert is a knowledge system of the forward production type. It monitors the corresponding joint response, and makes inferences on the basis of a set of performance specifications. These inferences are supplied to a fuzzy tuner at Level 3. The knowledge base of this fuzzy tuner consists of expert knowledge in the form of linguistic rules for servo tuning. This knowledge is matched with inferences of the servo experts to arrive at tuning decisions for the PID controllers. Using this structure, a control system has been developed for a two-degree-of-freedom robot. Performance of this controller is evaluated using simulation experiments.

Servo tuning and stabilization of nonlinear optical crystals

A new optical technique for servo tuning and stabilization of angle tuned nonlinear optical crystals is described. This technique has zero insertion loss and works equally well with collimated, focused, or noncollinear fundamental beams. Servo tuning of a Type I KDP nonlinear crystal for summing the output of a tunable dye laser with the Nd:YAG second harmonic and servo stabilization of the production of the Nd:YAG fourth harmonic in Type I KDP are demonstrated.

RF Power System for the Separated-Orbit Cyclotron Experiment

The SOCE is designed with 11 radio frequency cavities (injector - 3, buncher - 2, SOC - 6), each requiring up to 15 kW of rf drive power under full beam loading. A separate three-stage power amplifier unit using an Eimac 4CW25, 000A tetrode as the final amplifier is provided for each cavity. Each unit is provided with automatic servo tuning, and with precise phase and amplitude regulation. A master signal generator supplies a common 50-MHz drive signal, which also serves as the phase reference. Although requirements vary from one cavity to another, all power amplifier units are identical and connected to a single set of dc power supplies and controls. The components were designed conservatively so that the rf system could be operated at greatly increased power levels for high intensity beam studies, with only the addition of an auxiliary dc plate power supply. Most of the design features in the SOCE's multiple-amplifier radio frequency system will be directly applicable to later SOC-type accelerators, even for a much higher total rf power requirement.