Shiro Urushihara

Kalman filter-based disturbance observer and its applications to sensorless force control

Force estimation plays a very important role in many application areas. The disturbance observer is significantly becoming the preferred approach since it offers distinct advantages of improving the robustness of force control and the accuracy of force estimation. However, one of the main disadvantages is the limitation from white Gaussian noise. This paper proposes an improved design methodology for the disturbance observer. The main contribution of the work described in this paper is the design of disturbance observers combined with a Kalman filter with a multisensor system. From the experimental results, white Gaussian noise was reduced and fast response in contact motion was achieved. The effectiveness of the proposed disturbance observer has been confirmed through comparisons with conventional methods in 1-d.o.f. linear motor systems.

High performance sensor-less injection force control considering friction phenomenon

Recently, many of plastic products are mostly manufactured using injection molding machines. The quality of plastic products depends on the injection force. In a general force control system of the injection molding machine, the force information from the environment is detected by a force sensor. However, the force sensors present problems related to signal noise, sensor cost, narrow bandwidth, and other factors. We have proposed the reaction torque observer using two-inertia resonant model in our previous works. In the conventional estimation method, some estimated error causes at the pressure keeping process and the backing pressure process by the influence of nonlinear characteristics. The estimation accuracy of the state observer depends on the system identification because the actual system has the parameter variation and non-linear friction phenomenon. In this paper, we propose the new estimation method in which the influence of nonlinear factor is considered for high performance sensor-less force control. The effectiveness of the proposed method is confirmed by the simulation and experimental results.

High-performance sensorless injection force control based on nonlinear friction phenomenon

Currently, most plastic products are manufactured using injection molding machines. The quality of plastic products depends largely on the injection force. In a typical force control system of an injection molding machine, force information from the machine environment is obtained by a force sensor. However, force sensors have a few disadvantages in terms of signal noise, sensor cost, narrow bandwidth, etc. We have proposed the use of a reaction force observer based on the two-inertia resonant model. However, this method has some estimated error because of the influence of nonlinear characteristics of the holding process and the screw back-pressure process. The estimation accuracy of the reaction force observer depends on parameter variations and the non-linear friction phenomenon. This paper proposes a new injection force estimation method based on a proposed high-order reaction force observer, which is not influenced by the nonlinear friction phenomenon significantly. This paper evaluates the effectiveness and the sensorless feedback control of the proposed method through experiments.

Robust load position servo system without vibration and end-effector offset for industrial robots

This paper proposes a new robust load position servo system without mechanical vibration and end-effector offset for industrial robots. The compact high-gear reduction without backlash, such as the harmonic gear is frequently used in the driving system for the sake of high load-to-weight performance. Generally, the industrial robots have used the sensors mounted to actuator-side because hardware setting using load-side sensor is very hard to mount signal lines. Therefore, the end-effector response does not perfectly reach the desired position owing to the effect of external disturbance force, which is called end-effector offset. The proposed robust servo system uses the estimated load information due to repress the effect of external disturbance force. The proposed position servo system is designed based on the state & disturbance observer and robust speed control system using coprime factorization controller. The effectiveness of the proposed robust system is confirmed by experimental results of prototype mechanical system.

Analysis of interaction force of wire-based robot using variable wire rope tension control

In this paper, the objective is to analyze a robot system with consideration the different levels of wire rope tension for human-robot applications. In the controller design, dual disturbance observers with respect to two operation modes, namely the common mode and the differential mode are designed and applied for controlling wire rope tension and interaction force of human. The variable wire rope tension algorithm is proposed to change the mechanical bandwidth according to motion movements. The advantage points of the high mechanical bandwidth and low stiffness transmission are combined together. From the experimental results, the variable wire rope tension control is combined to give the best results on an experimental setup, for the rejection of the vibration effects and for the smooth interaction force.

Identification of twin direct-drive motor system with consideration of wire rope tension

An adaptable stiffness of mechanical using wire rope tension control, called as a twin direct-drive motor system, has unique advantages in human-robot interaction system, when compared with conventional industrial robot. Since the wire rope is low friction and lightweight device, it is possible to achieve high-efficiency, high degree of reliability, and safety. In this paper, modeling and closed-loop identification of the twin direct-drive motor system with wire rope tension are considered. After the swept-frequency sine wave injection and output data collection are finished, the Box-jenkins model is employed to identify the frequency response. From the simulation and experimental results, the total stiffness of the twin direct-drive motor system and the bandwidth of mechanical system can be increased by changing wire rope tension. This feature may make the twin direct-drive motor system very useful to provide a safety and smooth interaction force during operation. Therefore, it is suitable to implement with the human-robot applications for example, arm movement training robot and motion guide robot system.

Fine force control based on reaction force observer for electric injection molding machine

Currently, most plastic products are manufactured by using injection molding machines. The quality of plastic products depends largely on the injection force. In a typical force control system of an injection molding machine, force information from the machine environment is obtained by a force sensor. However, force sensors have a few disadvantages in terms of signal noise, sensor cost and narrow bandwidth. So, a sensor-less force detection method is desirable for electric injection molding machines. We have proposed the use of a reaction force observer based on the two-inertia resonant model. However, this method has some estimated error because of the influence of nonlinear characteristics of the holding process and the screw back-pressure process. This paper proposes a new injection force estimation method based on a proposed high-order reaction force observer (HORFO), which is not influenced by the nonlinear friction phenomenon significantly. This paper evaluates the possibility and versatility of the proposed sensor-less force control system by using proposed HORFO through experiments.

High-Performance Positioning System with Linear DC Servo Motor under Self-tuning Fuzzy Control

This paper describes a positioning system with a linear DC servo motor (LDM) under self-tuning fuzzy control. Two types of self-tuning fuzzy controllers (STFCs), one a model reference type, the other a feedforward type, are proposed. The objectives of these two types of STFCs are to repress the influence of nonlinear characteristics of the LDM and to improve the tracking performance. The fuzzy rules in the STFC are adjusted by a tuning algorithm so that the tracking error converges to zero. The effectiveness of the proposed STFCs for improvement of the tracking performance is demonstrated by the experimental results.This paper describes a positioning system with a linear DC servo motor (LDM) under self-tuning fuzzy control. Two types of self-tuning fuzzy controllers (STFCs), one a model reference type, the other a feedforward type, are proposed. The objectives of these two types of STFCs are to repress the influence of nonlinear characteristics of the LDM and to improve the tracking performance. The fuzzy rules in the STFC are adjusted by a tuning algorithm so that the tracking error converges to zero. The effectiveness of the proposed STFCs for improvement of the tracking performance is demonstrated by the experimental results.

Robust sensorless pressure control of electric injection molding machine using friction-free force observer

Injection molding is a common method for producing various resin products. The quality of the product significantly depends on the injection force. The accurate detection of the force is therefore very important to achieving in stable high-quality molding. The force control system of a typical injection molding machine obtains information about the force from the environment of the machine via a force sensor. However, because a force sensor often has disadvantages such as signal noise, high cost, and narrow bandwidth, a reaction force observer has been developed for electric injection molding machines. The high-order reaction force observer (HORFO) includes a friction compensation element and uses the dither signal insertion method. Although it neither affects the inserted dither signal nor the nonlinear friction phenomenon, steady-state errors remain in the pressure holding process because the torque transmission losses in the mechanical structures are not considered. In this paper, we propose a new Friction-Free Observer. We experimentally confirm the estimation performance of the proposed Friction-Free Observer using different driving points.

Force sensorless pressure control considering nonliner friction phenomenon for electric injection molding machine

Currently, most plastic products are manufactured using injection molding machines. The quality of products produced this way depends largely on the injection force. In the force control system of a typical injection molding machine, force information from the machines environment is obtained by a force sensor. However, these sensors have several disadvantages, which include signal noise, sensor cost, and a narrow bandwidth. Thus, sensorless force detection methods are desirable. The use of a reaction force observer, based on the two-inertia resonant model, has been proposed. However, this method is inaccurate due to the influence of nonlinear friction phenomenon. We have previously proposed a new injection force estimation method based on a high-order reaction force observer (HORFO), which is not significantly influenced by the nonlinear friction phenomenon. In this paper, an automatic parameter-switching HORFO (APS-RFO) is proposed to improve the estimation accuracy of HORFO. Moreover, this paper evaluates the possibility of a sensorless force control system using the proposed APS-RFO.