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Method for controlling parallel kinematic mechanism machine and control apparatus therefor

Method for controlling parallel kinematic mechanism machine and control apparatus therefor description/claims

This application is a Continuing Application of U.S. patent application Ser. No. 11/779,455, having a filing date of Jul. 18, 2007, and claims the benefit under 35 USC §119(a)-(d) of Japanese Patent Application Number 2006-216478 filed Aug. 9, 2006, the entireties of which are incorporated by reference.

1. Field of the Invention

The present invention relates to a method for controlling a parallel kinematic mechanism machine in which an end-effector, which is connected with a plurality of struts driven by actuators via joints, is moved by the struts, and to an apparatus for implementing the method.

2. Description of the Related Art

As a conventional method for controlling a parallel kinemtic mechanism machine, a method described in the Japanese Patent Application Laid-Open No. 2006-11752 is known. In this method, in a parallel kinematic mechanism machine, in order to obtain cutting resistance at the time of machining, in addition to the effect of feed resistance of an active shaft which is positively driven by actuators, disturbance is modeled with the rotational resistance generated in passive shafts which are not positively driven by the actuators, inertia term, and gravity term used as parameters, and each parameter is identified by the use of a disturbance observer to improve the machining accuracy. Now, in this method, all the passive shafts are not subjected but only a part thereof is modeled.

In addition, as conventional control apparatuses for machine tools, a control apparatus described in the Japanese Patent Application Laid-Open No. H05-285788 is known. This apparatus does not control focused on the parallel kinematic mechanism machine but performs control over diagnosis using loads of actuators of general machine tools. In this control, when the machine tool is normal, normal-time measurement data is obtained for loads of the actuators in advance, and this normal-time measurement data and the measurement data at the time of diagnosis are compared to diagnose.

By the conventional method such as the Japanese Patent Application Laid-Open No. 2006-11752, the accuracy is improved to some extent in that the rotational resistance of a passive shaft is considered in addition to the feeding resistance of an active shaft. However, since effects of the passive shafts which are not subjected are not considered, the error is increased by that much according to the conditions. In addition, the rotational resistance is identified by combinations with the factors in the conventional method. Thus, effects from the factors and effects of passive shafts blend together and error increase according to the conditions. Moreover, even when compensation using measurement values of rotational resistance in passive shafts is performed, interference with the factors occurs and high-accuracy compensation is not allowed to be obtained.

Therefore, the object of the invention according to first and fifth aspects is to provide a method for controlling the parallel kinematic mechanism machine and a control apparatus therefor that decides the end-effector position and posture with further improved accurately by performing compensation that purely extracts effects of rotational resistance only, by selecting all the passive shafts as objects for consideration and building up a model independent from effects of inertia, gravity, or the like.

In addition, the object of the invention according to ninth and tenth aspects is to provide a control method and a control apparatus of the parallel kinematic mechanism machine that eliminates effects of deformation errors of mechanical elements caused by rotational resistance and improves the estimation accuracy of kinematic parameters.

On the other hand, even when the conventional apparatus described in the Japanese Patent Application Laid-Open No. H05-285788 is simply applied to a parallel kinematic mechanism machine, diagnosis can be performed only under the measurement conditions related to the normal-time measurement data obtained in advance in a conventional apparatus. Thus, the measurement conditions at the time of diagnosis are restricted according to the conditions of the parallel kinematic mechanism machine, and it is difficult to perform accurate diagnosis when the measurement conditions differ from the measurement conditions related to the normal-time measurement data. Moreover, when detailed diagnosis targeted to specific struts or joints is performed, it is not clear under what measurement conditions, the normal-time measurement data should be obtained, and it is difficult to implement accurate diagnosis for specific struts or joints. Moreover, although normal/abnormal status of the struts or joints can be determined by comparing data with the normal-time data, it is difficult to specify abnormal joints or struts.

In addition, when a parallel kinematic mechanism machine is diagnosed, from the viewpoint of identifying abnormal portions, the control apparatus must grasp an increase of joint rotational resistance. However, in order to obtain the joint rotational resistance value, it is the only way to disassemble the joint and measure.

Therefore, the objects of the invention according to the eleventh and twelfth aspects and the sixteenth and seventeenth aspects are to provide a control method and a control apparatus of a parallel kinematic mechanism machine that can obtain the rotational resistance value of each joint easily and with high accuracy.

In addition, the objects of the invention according to the fifteenth and twentieth aspects are to provide a diagnosis control method and a diagnosis control apparatus of a parallel kinematic mechanism machine that can diagnose more accurately and also identify abnormal places by utilizing the obtained rotational resistance values at the time of diagnosis.

In order to solve the above problems, the invention according to the first aspect is a method for controlling a parallel kinematic mechanism machine having: a base fixed to the outside; a plurality of struts connected to the base via first universal joints; actuators which drive each strut; an end-effector connected to each strut via second universal joints; a control means for giving actuator command values to control each actuator; and a rotational resistance value storage means provided with the control means for storing rotational resistance values of the first universal joints and/or the second universal joints, the method including the steps of: a first step that determines each actuator command value for end-effector position command values and posture command values on the basis of predetermined kinematic parameters in the parallel kinematic mechanism machine; a second step that obtains rotational resistance values of first universal joints and/or second universal joints from the rotational resistance value storage means; a third step that computes the force and the moment exerted to each of the second universal joints by using the rotational resistance values; a fourth step that determines the resultant force and the resultant moment exerted to the end-effector from the force and the moment exerted to each of the second universal joints; a fifth step that computes an elastic deformation amount of a mechanism by using the resultant force and the resultant moment exerted to the end-effector and that computes the compensation amounts of the actuator command values using that amount; and a sixth step that updates the actuator command values determined in the first step with the compensation amounts determined in the fifth step taken into account.

In the invention according to a second aspect, in the third step, the links comprising struts, first universal joints, second universal joints are regarded as an independent serial link mechanism, respectively, and the force and the moment exerted to connections between the strut and the end-effector by rotational resistance of universal joints in relevant serial link mechanisms are computed in order to achieve the object of providing a control method that can perform highly accurate and efficient compensation with a small amount of calculation in addition to the above object.

In the invention according to a third aspect, in the third step, changes of rotational resistance values at the time of reversal of the first universal joints or the second universal joints are approximated by linear functions in order to achieve the object to provide a control method that can perform highly accurate compensation even at the time of reversing the first universal joints or the second universal joints in addition to the above object.

In the invention according to a fourth aspect, in the third step, the moving average processing is performed for the rotational resistance values of the rotary shaft which reverses at the time of reversal of the first universal joints or the second universal joints in order to achieve the object to provide a control method that can perform highly accurate compensation even at the time of reversing the first universal joints or the second universal joints in addition to the above object.

To solve the above-mentioned problems, the invention according to the fifth aspect is a control apparatus for a parallel kinematic mechanism machine including: a base fixed to the outside; a plurality of struts connected to the base via first universal joints; actuators which drive each strut; an end-effector connected to each strut via second universal joints; a control means for giving actuator command values to control each actuator; and a rotational resistance value storage means provided with the control means for storing rotational resistance values of the first universal joints and/or the second universal joints, wherein the apparatus includes: an actuator command value computing means to determine each actuator command value for end-effector position command values and posture command values on the basis of predetermined kinematic parameters in the parallel kinematic mechanism machine; a resultant force computing means that computes the force and the moment exerted to each of the second universal joints using the rotational resistance values obtained by rotational resistance value storage means, and determines the resultant force and the resultant moment exerted to the end-effector from the computed force and the moment exerted to each of the second universal joints; a compensation amount computing means that computes an elastic deformation amount of a mechanism by using the resultant force and the resultant moment exerted to the end-effector, and computes the compensation amounts of the actuator command values using that amount; and a control means that updates the actuator command values determined by the actuator command value computing means taking the compensation amounts determined by the compensation amount computing means into account.

In the invention according to a sixth aspect, the resultant force computing means regards as the links comprising struts, first universal joints, second universal joints as an independent serial link mechanism, respectively, and computes the force and the moment exerted to connections between the strut and the end-effector by rotational resistance of universal joints in relevant serial link mechanisms, in order to achieve the object to provide a control apparatus that can perform highly accurate compensation with a small calculation amount in addition to the above objects.

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