Kinematic Control
The primary purpose of an autonomous manipulation system is to perform intervention tasks with a limited exchange of information between the manipulator and the human supervisor. The information passed to the main control system is often only a high level
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Kinematic Control
The primary purpose of an autonomous manipulation system is to perform intervention tasks with a limited exchange of information between the manipulator and the human supervisor. The information passed to the main control system is often only a high level decision command, and the controller must be capable of following the command by providing reliable control references to the actuators. The main issue in designing and implementing a control system for autonomous manipulation is ensuring a reliable behavior within the workspace. A reliable behavior means also avoiding singularities, collisions, system instabilities and unwanted motions while performing the required task is theoretically executable. The control system must also address some general manipulation issues, such as being task-space oriented, with task priority assignments and dynamic priority changes. The third layer of the main control diagram of Fig. 3.1 is the Medium Level Controller of the system and it is the layer where the above issues are addressed. This Chapter describes some possible solutions to the inherent kinematical problems in a control system for autonomous manipulation. We chose a “task reconstruction” approach in order to automatically correct the required task according to the priority of the situation. For example, when approaching a singularity, in order to prevent unwanted motions and system instabilities the priority of the control system becomes maintaining the distance from the singularity over a predefined threshold, rather than following the input task. This approach is extendible to several other issues, such as collision avoidance, and ensures a reliable execution of the input task when it is theoretically feasible. If, for any reason, the input task cannot be executed, the control system must inform the above layer of the execution error, together with the nature of the problem (i.e. approaching a singularity).
G. Marani and J. Yuh, Introduction to Autonomous Manipulation, Springer Tracts in Advanced Robotics 102, DOI: 10.1007/978-3-642-54613-6_3, © Springer-Verlag Berlin Heidelberg 2014
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3 Kinematic Control
XBUS Client
XBUS Client Layer 5: VHLC
APL Client
FastBus
VHLC1: Control Station #1
APL Client VHLC2: Control Station #2
XBUS Server
X B U S (TCP-IP Data Exchange Bus)
xParser Server
APL Server
Layer 4 : HLC Arm Programming Language Server Trajectory planner
Kinematic Task priority
Singularity avoidance
Sensors Drivers
Healt monitor
Dynamics
Layer 3 : MLC (Kinematic controller)
Layer 2 : LLC Drivers
Manipulability
Colliision avoidance
Mechanical limit guard
Saturation guard
Layer 1 : VLLC Motors controllers
Layer 0 : Arm
Fig. 3.1 Control system
3.1 Generation of the Velocity Reference In this chapter we are not considering the inherent problem in the dynamic control of the manipulator. In our treatise, the arm together with its dynamic controller is considered as a separate subsystem, as shown in Fig. 3.2. The function of the kinematic controller described here is
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