Direct-drive Motor System Research Articles

Control of Interaction Force of Twin Direct-Drive Motor System Using Variable Wire Rope Tension With Multisensor Integration

In this paper, a novel wire-based robot system with consideration of the different levels of wire rope tension is introduced, and its performance while executing a task in an unknown environment is analyzed. An adaptable wire rope tension control, called a twin direct-drive motor system, provides a unique structure for a robot interaction system. Compared with conventional industrial robots, it significantly becomes the preferred approach for improving the level of reliability and providing safe user interaction because the wire rope mechanism is a low friction and lightweight device. In addition, from the identification results, the bandwidth of the robot system can be regulated by changing the wire rope tension. 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 the wire rope tension and interaction force. A variable wire rope tension algorithm is proposed to change the mechanical bandwidth based on the movements of a human. The advantages of a high mechanical bandwidth and low stiffness transmission are combined. With regard to the rejection of the vibration effects and the generation of a smooth interaction force, the variable wire rope tension control is found to give the best results in an experimental setup.

Force Control of Human–Robot Interaction Using Twin Direct-Drive Motor System Based on Modal Space Design

Future robot systems are required to focus on developing more flexible systems for use with human operator. These robots must operate more slowly and be more compliant to safe user interaction. This paper proposes an improved design methodology for the human-robot interaction system. The main contribution of the work described in this paper is the design of dual disturbance observers combined with modal space design for the twin direct-drive motor system. Two of the same direct-drive motors are required and connected by wire rope mechanism. Since both direct-drive motors have almost the same value of the friction effect and other nonlinearities, it is easy for the proposed system to compensate these deterioration effects. The proposed force control system is independently controlled in acceleration dimension by realizing the system based on common mode and differential mode. In the common mode, it is utilized for control of vibration suppression and wire rope tension. Moreover, the bandwidth and the stiffness of mechanism can be regulated by changing the wire rope tension control. In the differential mode, the purity of human external force with compensation of friction force is obtained. This mode is useful for control of the interaction force of human. The effectiveness of the proposed method is verified by experimental results.

Development and Analysis of a Wire-Based Robot With Twin Direct-Drive Motor System

In this paper, a sensorless wire rope tension control is introduced and analyzed to implement a wire-based robot with twin direct-drive motor system. Two of the same direct-drive motors are required and connected by wire rope mechanism. In the controller design, dual disturbance observers with respect to two control modes, namely the common mode and the differential mode are designed and applied for control of motion and wire rope tension. The wire rope tension in the common mode is controlled in order to regulate the mechanical bandwidth of the system. From the identification results, the high-tension of wire rope system is obtained a high mechanical bandwidth in the robot systems. The disturbance observer-based eliminates the need for the tension sensors, and may also be used to achieve the precise velocity and position control with the vibration-free performance in the differential mode. The effectiveness of the proposed method is verified by experimental results. It is shown that the high frequency responses are obtained by using high-tension of wire rope. The control performance may improve during the robot operation and, therefore, it is useful to compensate for the vibration effect.

Kalman-Filter-Based Sensor Integration of Variable Power Assist Control Based on Human Stiffness Estimation

In applications such as robot collaborating with human operators, the robot system must operate more slowly and be more compliant to safe user interaction. Moreover, a consideration of the dynamic properties of human operators is also important for the human application. According to such requirements, this paper presents a novel sensorless force control approach for the robot-assisted motion of the human arm. A twin direct-drive motor system with a wire rope has been developed to provide a precise force sensation and safety for human-robot interaction. In order to control the wire rope tension and human interaction force, two mode designs of the force control are realized. The common mode is utilized for the control of wire rope tension. In the differential mode, the Kalman-filter-based sensor integration for the interaction force observer is proposed in this paper. By combining two motor encoders and a commercial acceleration sensor together, white Gaussian noise is reduced, and high accurate feedback of the contact force is obtained. A variable power assist control method based on a real-time estimation of the stiffness of the human arm is also introduced. By considering the stiffness in human arm movements, this method increases the efficiency of the force control system and realizes comfortable force for human-robot interaction. The effectiveness of the method is verified by experimental results.

Structure of an Independent-wheel-system Bogie with a DDM and its Performance at High Speed

We have developed a new-concept bogie for gauge-changeable trains that is applicable to both standard gauge 1,435-mm line and meter gauge 1,067-mm line. The bogie must therefore feature good running stability at high speeds on standard gauge lines as well as high running performance on the curves of meter gauge line. It adopts a direct-drive motor system to enable the motor to be mounted directly to the wheels, an independent wheel system and a wheel-set steering system. The independent wheel system provides the bogie with good running stability at high speeds with a short wheelbase. We tested the model on our rolling stock test machine, and confirmed that no stability problems occurred at speeds of up to 500 km/h. We also conducted high-speed performance testing at the Transportation Technology Center Inc. in Pueblo, Colorado, USA, and on the Sanyo Shinkansen line in Japan at speeds of over 200 km/h.

DIRECT-DRIVE MOTOR SYSTEM WITH PARTICLE-TYPE ER FLUID DAMPER

In most of robotic systems in industrial applications, vibratory problems occur at high-speed motion, because of elasticity of drive systems like reduction gear units and mechanical structures. Also friction and backlash in the drive systems cause serious problems. On the other hand, since direct-drive (DD) motor systems do not use reduction gears, those are effective for high-speed and high-precision control. In DD motor systems, however, low damping ratio, or large time delays of computers and amplifiers causes another type of problem at precise positioning phase. In this study, a particle type ER fluid damper was introduced to a DD motor system to compensate damping ratio mechanically. Because controlling viscosity of ER damper according to status of motion did not disturb advantage of the DD system that can move fast, the performance of the DD system was improved. The effectiveness of the proposed system was confirmed experimentally. The method of our study can contribute to expansion of usability of ER fluid dampers on industrial applications not limited to DD systems.

Development of Gauge Change Bogies

For the gauge-changeable EMUs (free-gauge train), we have been developing two types of new gauge change bogies, types A and B. The type A bogie adopts the direct drive motor system to mount a motor directly on the side of a wheel, independent wheel system, and wheel-set steering system. The type B bogie adopts the cardan drive system. Both bogies can change the wheel gauge between the narrow gauge and standard gauge sections. This paper discusses their construction and mechanism to change the wheel gauge.

Mechatronics design of stiffness enhancement for direct‐drive motor system using ER variable damper

AbstractDirect‐drive (DD) motors have the characteristics of simple structure and high controllability without reduction gears or ball screws. However, DD motors are more sensitive to the disturbance torque and parameter variation than other motor systems, which have reduction gears. Enhancement of DD motor stiffness by increasing the gain is one of the effective methods to reduce this influence, but large gain will lead to instability and even vibration. Viewed from mechatronics design, an ER variable damper with a damping coefficient that can be changed depending on how the applicable voltage is designed, and directly attached to the shaft of the DD motor to achieve high servo stiffness. The structure and the damping coefficient model of the proposed ER variable damper are developed. The validation of this mechatronics design is demonstrated by a position PD (proportional derivative) control DD motor system with numerical simulations, which achieved both high stiffness and good stability for the controlled DD motor system. © 2002 Wiley Periodicals, Inc.

Study on High Gain Feedback Control of Direct-Drive Motor. (Application of Variable Damper Using Homogeneous ER Fluid).

Since a direct-drive(DD) motor system doesn't use the reduction gear, the structure of the servo system can be simple and stiff. On the other hand, in the DD system, the disturbance torque directly influences the accuracy of the control system. The high feedback gain is effective and important for reducing the influence of the disturbance. However, it easily makes the control system vibratory. Therefore, the servo gain has to be lowered for assuring stability, and this causes the influence of the disturbance large. In this study, we aim to realize the high gain feedback control and the DD motor system using an ER fluid damper is developed. By applying the ER damper to the DD motor system, it is possible to obtain the mechanical damping and to realize a high servo gain in the motion control. Finally, the effectiveness of the proposed system is confirmed experimentally.

Motion Control of Direct-Drive Motor by a Homogeneous ER Fluid

Since a direct-drive (DD) motor system doesn't have the reduction gear, the structure of the servo system can be simple and stiff. On the other hand, in the DD system, the disturbance torque directly influences the accuracy of the motor control. The high servo gain is effective and important for reducing the influence of the disturbance torque. However, the high servo control often makes the control system unstable or vibratory. Therefore, the servo gain must be lowered for assuring stability, and the influence of the disturbance becomes serious. In this study, the DD motor system using an ER fluid damper is discussed. By applying the ER damper to the DD motor system, it is possible to obtain the mechanical damping and to realize a high servo gain in the motion control. Finally, the effectiveness of the proposed system is confirmed experimentally.