Nominal Characteristic Trajectory Following Research Articles

Controller design for high-speed, ultra-precision positioning of a linear motion stage on a vibrating machine base stage control on a vibrating base

This paper presents a high-speed, ultra-precision point-to-point position control system design. It addresses precision stages with unknown characteristics, affected by machine base vibration and system effectiveness. The design is based on the nominal characteristic trajectory following (NCTF) control method, which can provide ultra-precision position control performance for the precision stages without accurate dynamic models. However, conventional NCTF control systems neither provide sufficient vibration suppression nor exhibit suitable vibration suppression characteristics. The position control performance is deteriorated by the machine base vibration. To overcome this problem, a procedure for incorporating a bandpass filter and derivative compensator in the NCTF control system is proposed and designed. These compensators exhibit high vibration suppression ability when combined, rather than when used individually. Additionally, they can be easily designed without any accurate dynamic model. The effectiveness of the compensator combination was first investigated using a linear model and subsequently experimentally verified. Using the proposed procedure, a control system was designed for the precision stage with friction characteristics on the vibrating machine base. The designed control system suppresses the residual vibration immediately after the target value becomes constant, and the error converges below 50 nm within 80 ms.

Practical high-precision motion control system based on nominal characteristic trajectory following control and simple feedforward element design methods

A practical design for a high-precision motion control system was formulated without an accurate dynamic model. The designed control system consisted of a nominal characteristic trajectory following (NCTF) control system—which can be easily designed without an accurate mechanical model—and time-invariant feedforward (FF) elements determined using a learning controller (LC). Specifically, an improved FF element design method, in which the LC was used to procedurally determine all the FF elements from the results of only four experiments, was used to enhance the motion control performance of the NCTF control system. To verify the effectiveness of the proposed framework, the NCTF control system was designed for a ball screw mechanism. This system was combined with the time-invariant FF element that is designed using the improved FF element design method. The performance of this system was compared with those of the conventional NCTF control system and the NCTF control system with the LC used as the FF element. The effectiveness of the improved FF element design method and combination of the determined FF elements and NCTF control system was experimentally demonstrated. Moreover, the enhancement in the position resolution of the FF element, which could compensate for the position-dependent factor in motion control, was verified. The average maximum error of this control system for the sinusoidal input with an amplitude of 0.2 mm and a frequency of 1 Hz is 0.209 μm, which is less than half the error of the other control systems.

Practical Control Strategy for Positioning Control of Pneumatic Artificial Muscles Driven Stage: Improved NCTF Control

This paper presents a practical control strategy for motion control of a pneumatic muscle actuated the system. Pneumatic artificial muscle (PAM) exhibits strong nonlinear characteristics which are difficult to be modeled precisely, and these characteristics have led to low controllability and difficult to achieve high precision control performance. This paper aims to propose nominal characteristic trajectory following (NCTF) control system, which emphasizes simple design procedure without the need of exact model parameters, and yet is able to demonstrate high performance in both point-to-point and continuous motions. However, the conventional NCTF controller does not offer a promising positioning performance with the PAM mechanisms, where it exhibits large vibration in the steady state before the mechanism stopping and tends to reduce the motion accuracy. Therefore, the objective of this study is to improve the conventional NCTF controller by removing the actual velocity feedback to eliminate vibration problem, added an acceleration feedback compensator to the plant model, and a reference rate feedforward to solve low damping characteristic of the PAM mechanism simultaneously improve tracking following characteristic. The design procedure of the improved NCTF controller remains easy and straightforward. The effectiveness of the proposed controller is verified experimentally and compared with the conventional NCTF and classical PI controllers in the performances of positioning and continuous motion. The improved NCTF controller reduces the positioning error up to 90% and 63% as benchmarked to the PI and conventional NCTF controllers, respectively, while it reduces up to 92% (PI) and 95% (NCTF) in the tracking error.

Positioning Control and Operational Evaluation of A One Mass Rotary System using NCTF Controller

A practical control scheme is proposed for a one mass rotary system. It was written to demonstrate the controller performance towards positioning and tracking control. For this system, the Nominal Characteristic Trajectory Following (NCTF) controller is proposed and improved. The objective of NCTF controller is to make the object motion to follow the NCT and ends at it origin. Generally, the NCTF controller consists of a Nominal Characteristic Trajectory (NCT) obtained from open loop response and Proportional Integral (PI) compensator. The CM-NCTF controller is proposed for evaluating the motion performance and compare with the conventional NCTF controller. For positioning control, both NCTF controllers demonstrate almost identical positioning performance. However, for tracking control, CM-NCTF controller demonstrates better tracking performance than the conventional NCTF controller with the smallest motion error presented. Besides, the robustness of the CM-NCTF controller to the variation load is examined.

Enhancing of nominal characteristic trajectory following control for motion systems

The goal of this paper is to enhance a practical nominal characteristic trajectory following (NCTF) controller that is specifically designed for two-mass point-to-point positioning systems. A nominal characteristics trajectory contained in the NCTF controller acts as movement/motion reference and a compensator is utilized to force the object to detect and follow the reference/desired trajectory. The object must follow and track closely and should be as fast as possible. The NCTF controller is designed with two different intelligent based compensator approaches which are fuzzy logic and extended minimal resource allocation network. The proposed controller which is NCTF are compared with the conventional proportional integral compensator. Then the results of simulation are discussed for the positioning performances. The inertia variations due to the effect of the design parameters are also assessed to see the robustness of controllers. The results show that the NCTF control method designed from an intelligent based compensator has a better positioning performance in terms of percentage of overshoot, settling time, and steady state error than the classical based compensator.

NCTF-FL Controller for Pendulum Balancing System

Pendulum Balancing of Linear Servo System consists of a cart driven by a DC motor, via a rack and pinion mechanism to ensure consistent and continuous traction. The cart is also equipped with a rotary joint to which a free turning rod (or pendulum) can be attached. This concept paper proposed a combination of Nominal Characteristic Trajectory Following (NCTF) and Fuzzy Logic (FL) to control the position of the cart and to balance the pendulum. The proposed controllers are expected to have a simple design method and achieved high performances.

Improvement of Fuzzy Based Practical Controller for Continuous Motion Control

This article presents a development of a fuzzy based nominal characteristic trajectory following (NCTF) controller for continuous motion control. A new structure is proposed in order to achieve excellent performance of tracking to a continuous reference input and also for point-to-point positioning task. The proposed structure maintains the NCTF controller simple configuration which is composed of a nominal characteristic trajectory (NCT) and a compensator. The compensator is based on a Mamdani type fuzzy controller. Its membership functions are designed according to the available information provided by NCT and the hardware specification. Controller performance was evaluated through simulation by comparing it with the existing method previously proposed for the fuzzy based NCTF controller. The tracking performance was evaluated by measuring responses of the system providing continuous sinusoidal signal input. The result indicates that substantial improvement is achieved in tracking of continuous reference inputs. Moreover, a better result is also obtained in performing point-to-point positioning task. DOI: http://dx.doi.org/10.11591/telkomnika.v13i1.7008

Practical Control for Two-Mass Positioning Systems in Presence of Saturation

The precision positioning systems generally need a good controller to achieve a fast response, high accuracy and robustness. In addition, ease, simplicity of controller design structure and high motion control performance are very important for practical applications. For satisfying these requirements, nominal characteristic trajectory (NCT) with proportional integral (PI) and notch filter (NF) as a compensator has been proposed as a practical control method for two-mass rotary PTP positioning systems. However, the effect of the actuator saturation cannot be completely compensated due to integrator windup when the object parameter varies. This paper presents a method to further improve nominal characteristic trajectory following (NCTF) controller to overcome the problem of integrator windup by adopting PI anti-windup schemes. The improved NCTF controller is evaluated experimentally using two-mass rotary positioning systems. The effect of the design parameters on the robustness of the improved NCTF with anti-windup integrator controller is evaluated and compared with NCTF without anti-windup integrator and the equivalent PID controller. The results show that the improved NCTF controller is effective to compensate the effect of integrator windup.

Practical Control for Two-Mass Positioning Systems in Presence of Saturation

The precision positioning systems generally need a good controller to achieve a fast response, high accuracy and robustness. In addition, ease, simplicity of controller design structure and high motion control performance are very important for practical applications. For satisfying these requirements, nominal characteristic trajectory (NCT) with proportional integral (PI) and notch filter (NF) as a compensator has been proposed as a practical control method for two-mass rotary PTP positioning systems. However, the effect of the actuator saturation cannot be completely compensated due to integrator windup when the object parameter varies. This paper presents a method to further improve nominal characteristic trajectory following (NCTF) controller to overcome the problem of integrator windup by adopting PI anti-windup schemes. The improved NCTF controller is evaluated experimentally using two-mass rotary positioning systems. The effect of the design parameters on the robustness of the improved NCTF with anti-windup integrator controller is evaluated and compared with NCTF without antiwindup integrator and the equivalent PID controller. The results show that the improved NCTF controller is effective to compensate the effect of integrator windup.

Improved NCTF Control Method for a Two-Mass Rotary Positioning Systems

This paper describes an improvement of the existing nominal characteristic trajectory following (NCTF) as a practical control method for a two-mass rotary point-to-point (PTP) positioning systems. Generally, the NCTF controller consists of a nominal characteristic trajectory (NCT) and a PI compensator. A notch filter is added as a part of the compensator to eliminate the vibration due to the mechanical resonance of the plant. The objective of the NCTF controller is to make the object motion follow the NCT and end at its origin. The NCTF controller is designed based on a simple open-loop experiment of the object. The parameters identification and an exact model of the plant are not necessary for controller design. The performance response of improved NCTF controller is evaluated and discussed based on results of simulation. The effect of the design parameters on the robustness of the NCTF controller to inertia and friction variations is evaluated and compared with conventional PID controller. The results show that the improved NCTF controller has a better positioning performance and is much more robust than the PID controller.

고진공 환경중 고출력 초음파 모터 이송 스테이지의 나노미터 위치 제어

본 연구는 고진공 환경중 초음파 리니어 스테이지의 나노미터 위치제어를 기술하고 있다. 고진공 환경 중 초정밀 위치 제어 시스템에 응용하기 위해 3 차 종진동 모드와 6 차 횡진동 모드를 가지는 BLT를 개발 했다. 안정적인 고출력을 위해 BLT 는 하나의 공진 주파수로 두 개의 모드 진동을 발생 시켜야한다. 하나의 공진 주파수를 이용 하기 위해 어드미턴스를 변화시켜 각 모드의 공진 주파수를 일치시켜 조건이 다른 대기 환경에서 안정적인 고출력을 얻을 수 있었다. 기압 변화에 따라 구동 특성이 달라지는 시스템을 제어하기 위해 마찰력 변화에 따른 비선형 특성을 보상한 NCTF 제어를 사용했다. 설계된 제어기를 이용해 고진공 환경에서 시스템을 나노미터 정도로 제어하는 결과를 얻을 수 있었다.

Practical controller design for precision positioning, independent of friction characteristic

In this contribution, a practical controller design for non-contact mechanism and contact mechanism is discussed. The design procedure is applicable and totally independent of friction characteristic. Thus, designer does not need to consider the friction characteristic of a mechanism and it is a valuable controller approach in industry. The practical controller design procedure which based on current Nominal Characteristic Trajectory Following (NCTF) controller is proposed and improved. The NCTF controller is comprehensive, comprising of a Nominal Characteristic Trajectory (NCT) and a PI compensator, which is free from exact modeling and parameter identification. In NCTF controller design, the NCT is constructed from the open-loop responses of the mechanism. The designed input signal for open-loop experiment is needed to satisfy the following two conditions: (1) the displacement by the input signal must be smaller than the working range of the mechanism to avoid any damage to the mechanism; (2) the suitable input signal needs to produce sufficient rapid and smooth response during deceleration to satisfy the desired specifications because the response significantly influences the reference following characteristic of the control system. So far, the NCTF controllers had been implemented to the mechanisms which have sufficient large damping characteristics and it was natural to satisfy the condition (1). However, non-contact and low damping mechanisms do not have sufficient damping characteristics. Since the high damping characteristics of the mechanism have been used before, the condition (2) is still not yet been considered. Therefore, the design procedure of the input signal satisfying the two conditions is proposed and verified by experiments in this paper. The common conditions of the input signal which is independent of friction characteristic of the mechanisms are discussed. Then, the experimental verifications are performed using non-contact mechanism and contact mechanism. In this paper, the performance evaluation is discussed separately in two parts. In part 1, by using the non-contact mechanism, the positioning results of two different NCTs are compared in order to show the usefulness of the modified suitable input. In part 2, the contact mechanism is used to show the effectiveness of the NCTF controller with its simple and practical design procedure, which is independent of friction characteristic. The effectiveness of the Continuous Motion NCTF controller is verified with the PID controller experimentally in positioning control and tracking control. The experimental results prove that the displacements of the open-loop responses for NCTs are always smaller than the working range and the design procedure of the input signal is successfully independent of the friction characteristic of the mechanism. Overall, the Continuous Motion NCTF controller which has simple and practical design procedure exhibits the high performance in positioning and tracking control with contact mechanism and non-contact mechanism, as compared to the PID controller. The PID controller shows the low adaptability in motion control performances for both conditions of mechanism.

Fast Precision Positioning of a Ball Screw Mechanism Based on Practical NCTF Control

We discuss improvements in a practical nominal characteristic trajectory-following (NCTF) controller for fast positioning. The NCTF controller consists of a nominal characteristic trajectory (NCT) as the movement reference and a PI compensator making object movement follow the NCT. It is easily designed without an exact model, known parameters, or much control theory knowledge. The step speed of NCTF control depends on the NCT. We introduce two ways to construct the NCT for high-speed step movement, - fast positioning is introduced and the performances by two NCTs thus constructed are compared to clarify a more suitable way using two ball screw mechanisms. Experiments in positioning with the NCT by the suitable way are evaluated, whose results show that the NCT increases step speed while preserving the robustness of feature step height and movable mass changes.

Fuzzy Anti-windup Schemes for NCTF Control of Point-to-point (PTP) Positioning Systems

The positioning systems generally need a controller to achieve high accuracy, fast response and robustness. In addition, ease of controller design and simplicity of controller structure are very important for practical application. For satisfying these requirements, NCTF (nominal characteristic trajectory following) controller has been proposed as a practical PTP positioning control. However, the effect of actuator saturation can not be completely compensated due to integrator windup because of plant parameter variations. This study presents a method to improve the NCTF controller for overcoming the problem of integrator windup by adopting fuzzy anti-windup schemes. Two fuzzy anti-windup schemes based on Mamdani and Takagi-Sugeno fuzzy system are developed and evaluated their effectiveness. The improved NCTF controller with the proposed fuzzy anti-windup schemes is evaluated through simulation using dynamic model of a rotary positioning system. The results show that the improved NCTF controller with Takagi-Sugeno-based fuzzy windup is the best scheme to compensate for the effect of integrator windup.

Robustness evaluation of three friction compensation methods for point-to-point (PTP) positioning systems

Friction is one of the major contributing factors to problems associated with accuracy in positioning systems. The positioning accuracy problem becomes more complicated because of variations in the friction. In this paper, three simple friction compensation methods for the point-to-point (PTP) positioning system, which are easily applied in practical applications, are compared and evaluated experimentally on an experimental rotary positioning system. The first controller is the nominal characteristic trajectory following (NCTF) controller and the other two are the PD controller with a discontinuous non-linear proportional feedback (DNPF) compensator and the smooth robust non-linear feedback (SRNF) compensator. All of the controllers are compared in terms of the effectiveness of the controller to compensate for the friction as well as robustness against inertia and friction variations. The results demonstrate that the NCTF controller is more robust against friction variation than the PD controller with the DNPF or SRNF compensator.

Practical control of precision positioning mechanism with friction

This paper describes the practical control of precision positioning mechanisms with friction. In a controller design, the microdynamic characteristic of these mechanisms is taken into account. First, the behavior of an experimental mechanism immediately before stopping is examined experimentally and its characteristics, namely, the micro- and macrodynamic ones are modeled. Next, a practical control method is proposed for the mechanism. The controller is designed based on the nominal characteristic trajectory following (NCTF) controller design procedure. It consists of a nominal characteristic trajectory (NCT) and a PI compensator. The NCT is determined using an open-loop time response of the mechanism and is represented on a phase plane. The compensator is used to make the mechanism motion follow the NCT and to stop the motion at the origin of the phase plane. Although the compensator is designed based on the microdynamic characteristic, it is useful in a wide working range. The positioning performance of the system with the proposed controller is examined in comparison with those of the system with conventional PID controllers. These results prove that the system with the proposed controller has a better positioning performance than those with conventional PID controllers and its positioning resolution is higher than 50 nm.

Characteristics of practical control for point-to-point (PTP) positioning systems: Effect of design parameters and actuator saturation on positioning performance

In this study, a nominal characteristic trajectory following (NCTF) controller for point-to-point (PTP) positioning systems is introduced and its performance is evaluated. The NCTF controller consists of a nominal characteristic trajectory (NCT) and a compensator. The objective of the NCTF controller is to make the object motion follow the NCT and end at its origin. Therefore, the NCT is used as an intended object motion and the compensator is used to make the motion of the controlled object follow the NCT. The NCTF controller is designed based on a simple open-loop experiment of the object and no information except the NCT is necessary for controller design. The effectiveness of the NCTF controller is evaluated and discussed through simulations and experiments using an experimental rotary positioning system. The effect of the design parameters on the robustness of the NCTF controller to inertia and friction variations is evaluated and the influence of saturation on the positioning performance is examined. Moreover, the effects of the saturation on the positioning performance and robustness are compared with those of conventional PID ones. It is proved that the NCTF controller is much more accurate and robust to inertia and friction variations than the PID controllers, even if the saturation occurs.