Yuzuru Ohba

Sensorless Force Control for Injection Molding Machine Using Reaction Torque Observer Considering Torsion Phenomenon

Recently, many plastic products have been produced and used. These plastic products are mostly manufactured using injection molding machines. The quality of plastic products depends on the injection force. Therefore, it is important to develop a fine force-control system. Generally, in force-control systems, the force information from the environment is detected by a force sensor. However, control systems using force sensors present problems related to signal noise, sensor cost, narrow bandwidth, and other factors. To overcome these problems, this paper presents a proposal for a new sensorless force-control method using a reaction torque observer. The injection molding machine, which uses a ball screw, has a resonance frequency that is affected by the torsion phenomenon. This new reaction torque observer considers the torsion phenomenon and friction phenomena.

Sensor-less force control for injection molding machine using reaction torque observer

In recent years, the industrial researchers have paid attention to the not only position control but also force control. The one target of force control researches is the injection molding machine. The conventional force control system uses the force sensor to detect the inserted force. However, the force control system using force sensor has some problems such as the noise, the frequency band and so on. This paper newly proposes that the reaction torque observer is applied to the injection molding machine using ball screw. The reaction torque observer solves this problem of force sensor. However, it is well-known that the ball screw system has the resonant frequency caused by the torsion phenomenon. Hence, this torsion vibration affects both performances of force control and reaction torque estimation. This paper proposes a new reaction torque observer considering the torsion phenomenon and the friction torque. The proposed reaction torque observer estimates the reaction torque accurately. Moreover, as the outside of proposed reaction torque observer has its friction model, this friction model can be tuned without considering the stability condition of force control feedback system. The validity of proposed force control system is confirmed by the experimental results. This paper realizes the low cost and space-saving injection molding machine by using the proposed force sensor-less control method.

Sensor-less Force Control for Machine Tool Using Reaction Torque Observer

In recent years, a force control system is applied to many applications. There is much research about force control for machine tools. Generally, in force control systems, the force information from the environment is detected by force sensor. However, the control system using force sensor has some problems, such as signal noise, colocation problem and narrow bandwidth. This paper proposes a new force sensor-less control system using a reaction torque observer. The proposed control method is applied to a machine tool using ball screw. Since the actuator using ball screw and timing belt has a torsional vibration phenomenon, the proposed reaction torque observer should consider this torsional vibration. As a result, this paper realizes the sensor-less control for machine tool using reaction torque observer. The validity of the proposed force control method is confirmed by several experimental results.

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.

Friction free bilateral robot based on twin drive control system considering two resonant frequencies

This paper proposes a new friction free bilateral system based on twin drive control system considering its resonant frequency. The twin drive system consists of two motors that are coupled by the differential gear. The output torque becomes a differential torque of both motors. The nonlinear friction torque of the twin drive system is easily compensated. However, this system has the resonant frequencies and the anti-resonant frequencies which are caused by the torsional vibration. This paper proposes a new three-inertial-model of twin drive system, and identifies the resonant frequencies and its friction torque. This paper proposes a new vibration suppression controller for the three-inertial model without high order control system. Therefore, the operationality of bilateral teleoperation is improved by the proposed system.