Control system for grasping force of a manipulator for grasping objects

A manipulator comprising:

• a grasping mechanism for grasping an object with a controllable grasping force;
• an arm mechanism coupled to said grasping mechanism and arranged to be capable of being raised to lift said object grasped by said grasping mechanism;
• grasping force control means coupled to said grasping mechanism for controlling a grasping force applied to said grasping mecansim to grasp the object;
• weight detecting means coupled to said arm mechanism for detecting a force on said arm mechanism;
• grasping detecting means responsive to said weight detecting means for detecting whether or not the grasped object has been lifted up by a present force being applied to said grasping mechanism;
• and
• grasping force selecting means coupled to said grasping force control means and responsive to said grasp detecting means for stepwise increasing therefore a grasping force being applied to said grasping mechanism by said grasping force control means from a predetermined minimum force level until said grasp detecting means detects that the object has been lifted;
• said grasping force selecting means including;
• counter means for counting peaks generated in an output signal of said weight detecting means which occur due to slippage between the object and said grasping mechanism;
• and memory means for storing, in different memory locations of said memory means which are designated by count values of said counter means, data representing levels of grasping forces to be applied to said grasping mechanism which stepwise increase from the predetermined minimum force level, said memory means being coupled to said counter means, so that grasping force data corresponding to a count value of said counter means is read out of said memory means and applied to said grasping force control means to apply to said grasping mechanism a grasping force corresponding to the count value in said counter means;
• and
• said grasp detecting means including;
• peak detecting means for detecting the peaks generated in the output signal of said weight detecting means;
• hold means coupled to said weight detecting means and said peak detecting means and responsive to detection of a first peak in the output signal of said weight detecting means for holding a first peak value in the output signal of said weight detecting means;
• multiplying means coupled to said peak hold means and counter means for multiplying the first peak value held in said peak holds means by a value corresponding to a count value in said counter means;
• and
• comparing means coupled to said multiplying means and said weight detecting means for comparing the level of the output signal of said weight detecting means with the level of an output signal of said multiplying means, wherein the output signals of said comparing means and said peak detecting means are adapted to increment said counter means in said grasping force selecting means.

A manipulator comprising:

• a grasping mechanism for grasping an object with a controllable grasping force, the frictional force between said grasping mechanism and said object varying from static frictional force to dynamic frictional force when a slippage occurs between said grasping mechanism and said object;
• an arm mechanism coupled to said grasping mechanism and arranged to be capable of being raised to lift said object grasped by said grasping mechanism;
• grasping force control means coupled to said grasping mechanism for controlling a grasping force applied to said grasping mechanism to grasp the object;
• weight detecting means coupled to said arm mechanism for detecting a force applied to said arm mechanism when the grasped object is being lifted, the force applied to said arm mechanism instantaneously varying in response to the variation of the frictional force between said grasping mechanism and said object from the statical frictional force to the dynamic frictional force;
• grasping detecting means coupled to said weight detecting means for detecting whether or not the grasped object has been lifted by a present force being applied to said grasping mechanism, said grasping detecting means being arranged to detect that said object has not been lifted, in response to the detection of the instantaneous variation of the frictional force between said grasping mechanism and said object by said weight detecting means;
• and
• grasping force selecting means coupled to said grasping force control means and responsive to said grasp detecting means for stepwise increasing a grasping force being applied to said grasping mechanism by said grasping force control means from a predetermined minimum force level until said grasp detecting means detects that the object has been lifted.