Vision-Based Hybrid Controller to Release a 4-DOF Parallel Robot from a Type II Singularity

Abstract

The high accuracy and dynamic performance of parallel robots (PRs) make them suitable to ensure safe operation in human–robot interaction. However, these advantages come at the expense of a reduced workspace and the possible appearance of type II singularities. The latter is due to the loss of control of the PR and requires further analysis to keep the stiffness of the PR even after a singular configuration is reached. All or a subset of the limbs could be responsible for a type II singularity, and they can be detected by using the angle between two output twist screws (OTSs). However, this angle has not been applied in control because it requires an accurate measure of the pose of the PR. This paper proposes a new hybrid controller to release a 4-DOF PR from a type II singularity based on a real time vision system. The vision system data are used to automatically readapt the configuration of the PR by moving the limbs identified by the angle between two OTSs. This controller is intended for a knee rehabilitation PR, and the results show how this release is accomplished with smooth controlled movements where the patient’s safety is not compromised.

Using a Development Platform with an STM32 Processor to Prototype an Inexpensive 4-DoF Delta Parallel Robot

“…Selected settings of the controller for an object described with an Equation ( 25) are shown in Table 2. PID control described with the following relation (26) was used in the simulation tests of the manipulator control system (Figure 14): ( ) The control of the angular position of the various arms of the designed active manipulator was based on the PID control. Matlab software and its composite package Simulink were used in order to choose the settings of the controller.…”

“…PID control described with the following relation (26) was used in the simulation tests of the manipulator control system (Figure 14): ( ) Selected settings of the controller for an object described with an Equation ( 25) are shown in Table 2. PID control described with the following relation (26) was used in the simulation tests of the manipulator control system (Figure 14): In order to compare the quality of the adjustment of the control system with the con troller settings chosen with the use of auto-tuning method, settings of PID controller wit the use of the method based on the approximation of the parameters of the fluctuatin response were determined. For this purpose, Matlab environment was exploited, in whic an application which allows fulfilling this task was prepared.…”

“…The constructional range of platform movement is only ±45°. Thus, in a prototype construction, the constructors of Par4 [ 25 , 26 , 27 ] robots applied a special multiplying mechanism which enables a full movement ±180°. Robots have a belt drive (1:4 position) with the first wheel rigidly fixed on the first part of the moveable platform, and the second one joined with the second main part of the articulated quadrangle of the platform with the use of a rotating joint.…”

Editorial of Special Issue “Combining Sensors and Multibody Models for Applications in Vehicles, Machines, Robots and Humans”

“…The objective of the third work [ 3 ] is to avoid the danger of reaching singular positions in a parallel robot for rehabilitation. For this purpose, a control system is developed based on computer vision and the multibody model of the robot.…”

“…In summary, it can be seen that the papers gathered in the Special Issue contributed either by proposing solutions to the general problem of state, input and/or parameter estimation [ 4 , 5 , 7 , 8 , 9 ], and/or by suggesting applications of the combined use of sensors and multibody models to different fields, such as automotive [ 6 , 8 , 9 ], railway [ 2 ], naval [ 5 ], spatial [ 10 ], machinery [ 4 , 7 ], robotics [ 3 ], biomechanics [ 1 ] and music [ 6 ] applications, thus showing the theoretical challenges and practical interest of this research topic.…”