Force, Stiffness and Viscous Damping Control of a Stewart-Platform-Type Ankle-Foot Rehabilitation Assist Device with Pneumatic Actuator

2013 ◽  
Vol 25 (6) ◽  
pp. 897-905 ◽  
Author(s):  
Takayuki Onodera ◽  
◽  
Eiji Suzuki ◽  
Ming Ding ◽  
Hiroshi Takemura ◽  
...  
Keyword(s):  
Ankle Joint ◽  
Force Control ◽  
Physical Therapists ◽  
Viscous Damping ◽  
Mean Square ◽  
Assist Device ◽  
Link Mechanism ◽  
Parallel Link ◽  
And Control ◽  
Ankle And Foot

The number of physically disabled people in need of rehabilitation is increasing. Unfortunately, there is a shortage of physical therapists specializing in such rehabilitation. This has increased the demand for rehabilitation assist devices that can lessen the burden of physical therapists. In this study, the authors develop a device that can assist in the rehabilitation of the ankle joint by employing a Stewart-platform (SP)-type parallel-link mechanism. With the SP-type parallel-link mechanism, it is possible to measure and control six degrees-of-freedom (DOFs) of ankle-foot movement during rehabilitation. Because the device enables the measurements of the ankle and foot, it is possible to calculate the instantaneous center of the ankle joint. In previous studies, the authors proposed methods to calculate and control the posture of the ankle and foot by an SP-type parallel-link mechanism and verified their accuracy. In this paper, the authors propose a method for force control using the device and also verify its accuracy. Using this device, the force acting on the ankle-foot can be controlled by six air cylinders. The force produced by a single air cylinder is determined by controlling the pressures in the extension and retraction directions. The accuracy of the force control method is verified for a single air cylinder and for the assist device when all six air cylinders are engaged. Results show that the accuracy of the single air cylinder has a mean square error of 0.24 N or less, while those for force control of the entire device are 4.2 N or less for parallel translation and 3.2 Nm or less for rotation. This demonstrates a satisfactory accuracy. To incorporate rehabilitation assistance by means of stiffness or viscous damping in the future, the authors also propose methods to control the coefficients of stiffness and viscous damping of the air cylinder and verify their accuracy. The mean square errors for the accuracies in controlling the coefficients of stiffness and viscous damping are 3.4 N/m and 1.4 Ns/m, respectively, thus verifying the validity of the proposed methods.

scholarly journals Mechanical Design and Control of 3-DOF Active Scanning Probe Using Parallel Link Mechanism

2011 ◽  
Vol 5 (2) ◽  
pp. 86-90 ◽  
Author(s):  
Takashi Harada ◽  
◽  
Ke Dong ◽  
Keyword(s):  
Optimum Design ◽  
Force Control ◽  
Impedance Control ◽  
Numerical Control ◽  
Scanning Probe ◽  
Position Sensing ◽  
End Plate ◽  
Link Mechanism ◽  
Parallel Link ◽  
Active Scanning

A 3-DOF active scanning probe using a Parallel Link Mechanism (PLM) is proposed. It employs a small touching force control and can be used for small position sensing devices which works within sizes of few millimeters. The device is attached to the tip of coordinate measuring machines or numerical-control machine tools and used as a scanning probe. In this paper, the characteristics of the mechanism, optimum design, and a control system of the PLM are introduced. The kinematics and differential relations of the PLM are derived. An optimum design for the PLM is proposed as that in which the mechanism’s manipulability is equal in all directions. This implies that the force and position sensitivities of the PLM share an isotropic relationship. A prototype of the PLM is developed. The PLM is constructed on three voice coil motors that are vertically aligned on a base plate, and a sensing stylus is fixed on an end plate. Universal joints with ball bearings are developed for reducing the joint resistance. Position and force control methods for the scanning probe are introduced. For stable scanning motion, a disturbance observer-based mechanical impedance control is formulated. An experimental system for measuring the position of the probe using image processing is developed. It is found that the standard deviation of the positioning error along the z direction is less than 3 µm, whereas those along the x and y directions is larger because of the tilt of the end plate caused by alignment errors of the PLM’s mechanical parts.

Magnetic Linear Motion Mechanism of a 2-Parallel-Finger Hand for Force Operation

2003 ◽  
Vol 15 (6) ◽  
pp. 624-631 ◽  
Author(s):  
Tatsuya Nakamura ◽  
◽  
Zhiqi Liu
Keyword(s):  
Force Control ◽  
Experimental System ◽  
Magnetic Suspension ◽  
Linear Motion ◽  
Motion Mechanism ◽  
Displacement Sensors ◽  
Absolute Positioning ◽  
Link Mechanism ◽  
Mobile Telephones ◽  
Parallel Link

Besides assembling, processes like drilling, cutting and pasting are required in various operations in manufacturing of small sized mechanics such as watches, mobile telephones etc. Force control is essential to those dexterous operations. Also absolute positioning of micro-manipulators is required for their autonomous operations. For this purpose, a linear motion hand with two parallel fingers was proposed. It uses a novel parallel link mechanism for linear motion and controls the endeffector by measuring its position with displacement sensors. It uses magnetic suspension technology so that fine force control is realized. An experimental system composed of two one-finger units is presented. The accuracy of positioning is a few μm with a range of tens mm. The accuracy of force control is 3 mN with a range of hundreds gf. The effectiveness of the proposed hand was verified by the application to drilling and fitting.

Mechanism and Control of Parallel-Wire Driven System

2015 ◽  
Vol 27 (6) ◽  
pp. 599-607 ◽  
Author(s):  
Hitoshi Kino ◽  
◽  
Sadao Kawamura ◽  
Keyword(s):  
Robot Manipulators ◽  
Parallel Mechanisms ◽  
Serial Link ◽  
Parallel Wire ◽  
Link Mechanism ◽  
Human Arm ◽  
Driven System ◽  
Parallel Link ◽  
And Control ◽  
Controlled Object

<div class=""abs_img""><img src=""[disp_template_path]/JRM/abst-image/00270006/01.jpg"" width=""300"" /> A parallel-wire driven system</div>Many of the conventional robot manipulators have a serial-link mechanism to imitate a human arm. In recent years, however, industries have been aggressive in putting parallel-link mechanisms into practical use to cope with various problems that no conventional serial-link mechanisms have ever been able to solve. Under the circumstances, this paper describes a parallel-wire driven system, one of the parallel mechanisms. It is a system to drive a controlled object with flexible and light wires instead of rigid links. It has many advantages over conventional serial-link mechanisms or other ordinary parallel-link mechanisms. This paper first overviews previous studies on parallel-wire driven robots, and then details the mechanism and control of these systems, as well as examples of their application.

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