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Method and device for the improvement of the pose accuracy of effectors on mechanisms and for the measurement of objects in a workspace

  • US 20020013675A1
  • Filed: 05/14/2001
  • Published: 01/31/2002
  • Est. Priority Date: 11/12/1998
  • Status: Active Grant
First Claim
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1. A method for improving the pose accuracy of a mechanism in a workspace, wherein the mechanism is movable in at least one axis with tolerances and includes an effector, at least one effector object is mounted via a rigid connection to the effector eccentric to the at least one axis of the mechanism in an estimated pose with a tolerance in position and orientation, at least one reference object is arranged in the workspace with a tolerance in position and orientation, and a computer system is connected to the mechanism having a measurement control program, a parameter identification program, and a mechanism control program, the at least one effector object and the at least one reference object forming at least one trigger/detector pair comprising a signal trigger device and a signal detector for triggering and detecting a binary signal, wherein a totality of signal poses of the signal detector relative to the trigger device in which a signal is triggered on the signal detector is described by at least one non-trivial characteristic equation, said method comprising the following steps:

  • (a) selecting a proximity sequence N of a finite number of proximity poses for the at least one trigger-detector pair, each of the proximity poses being located in the vicinity of a respective one of signal poses, wherein the proximity sequence N is selected such that the following criteria are fulfilled;

    DG(N)≧

    DG(AI)/15whereby the distance on an arbitrary straight line G between two neighbouring points of the projection of the proximity sequence N onto G is at the most DG(N)/4, wherein DGis a function which maps each subset of the set A1 to the distance between those two points of the projection of this subset on G which are at maximum distance from each other on G;

    AI is the space of all those reachable effector poses of the given mechanism which result from elementary kinematic calculations on the basis of the known mechanism model which in turn is afflicted with tolerances;

    G is an arbitrary straight line which contains at least two points of SI; and

    SI is a subset of AI which is denotes the space of proximity poses and is defined by the totality of all those effector object poses where a signal would be expected according to a mathematical calculation based on the parameter values of the known tolerance-afflicted mechanism model, the estimated pose of the reference objects in space, and the estimated pose of the effector object on the mechanism;

    (b) searching for a nearby signal pose for each of the proximity poses consecutively through movement of one of the at least one effector object and the mechanism using a simple search algorithm until a signal pose is detected;

    (c) passing a momentary joint configuration of the mechanism onto the computer system after the detection thereof in said step (b) and storing the momentary joint configuration in the computer system as a data record;

    (d) using a parameter identification program to identify the true values of one of the parameters influencing the pose accuracy of the mechanism and user-specific subsets of this parameter set, whereby a scaling factor is used for the identification of all length-parameters.

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