Passive six-axis parallel feedback controlled machine capable of compensation and compensating method for using the same

Abstract

A six-axis parallel feedback control robot includes a mobile platform, a base platform, a controller, and six linear elastic elements connected between the mobile platform and the base platform via multiple joints. The mobile platform has an initial pose determined by the free lengths of the six linear elastic elements. The controller performs the following actions: calculating the compression of each linear elastic element and the corresponding support force when the mobile platform receives an external force; calculating the forward kinematics based on the compression to obtain the current pose of the mobile platform; calculating the equivalent force and equivalent moment of the mobile platform relative to the external force based on the current pose and the support forces of each linear elastic element; comparing the current pose with the initial pose to calculate the displacement of the mobile platform; and generating path compensation for the transfer platform cooperating with the six-axis parallel robot based on the equivalent force, equivalent moment, and displacement.

Claims

1. A passive six-axis parallel feedback control machine with compensation function, comprising: A mobile platform having a first surface; A base platform having a second surface; Multiple first joint elements are respectively disposed on the first surface; Multiple second joint elements are respectively disposed on the second surface; six passive linear elastic elements are respectively disposed between the moving platform and the base platform through the multiple first joint elements and the multiple second joint elements, and each passive linear elastic element has a passive elastic element and a linear sensor, wherein each passive elastic element has a free length, and the moving platform has an initial pose determined by the free length of each passive elastic element; and a controller is connected to the six passive linear elastic elements and performs the following actions: Action a) When the moving platform receives an external force, receive a compression amount of each passive elastic element measured by each linear sensor, and calculate a support force of each passive elastic element relative to the external force based on the compression amount; Action b) Calculate a positive kinematics based on the compression amount of each passive elastic element to obtain a current pose of the moving platform; Action c) Calculate an equivalent force and an equivalent moment of the moving platform relative to the external force based on the current pose and the support force of each passive elastic element; Action d) Compare the initial pose and the current pose of the mobile platform to obtain a displacement; and action e) generate a path compensation amount required for a transfer platform to cooperate with the passive six-axis parallel feedback control machine based on the effects, the effect moments and the displacement.

2. The passive six-axis parallel feedback control machine as described in claim 1, wherein the linear sensor is an optical ruler or a laser rangefinder.

3. The passive six-axis parallel feedback control machine as claimed in claim 1, wherein each of the passive elastic elements has a stiffness coefficient, and the controller is configured to calculate the compression amount in the action a) based on the difference between a current length and the free length of each passive elastic element, and to calculate the support force of each passive elastic element based on the compression amount and the stiffness coefficient of each passive elastic element according to Hooke's law.

4. The passive six-axis parallel feedback control machine as claimed in claim 1, wherein the controller is further configured to determine, based on the displacement, whether at least one of the plurality of passive elastic elements is approaching or reaching a structural limit, and to issue a request command to request the transfer platform to stop moving when any of the passive elastic elements approaches or reaches the structural limit.

5. The passive six-axis parallel feedback control machine as described in claim 1, wherein the transfer platform comprises: A host controller is connected to the host controller and receives the path compensation amount; A robotic arm is connected to the host controller and is mounted on the base platform; wherein the host controller adjusts a motion command for controlling the movement of the robotic arm based on the path compensation amount, so that the center point of the moving platform remains in the initial pose when the robotic arm moves.

6. The passive six-axis parallel feedback control machine as claimed in claim 1, wherein the controller is configured to iteratively perform the following actions to achieve action b): obtaining the current pose of the mobile platform and calculating an inverse kinematics based on the current pose to obtain a current length of each of the passive elastic elements; calculating a length error value between the current length of each passive elastic element and a target length caused by the external force; calculating a linear displacement velocity array required for each passive elastic element based on the length error value and a time constant of an iterative algorithm; calculating a Jacobian matrix based on the current pose of the mobile platform and using the Jacobian matrix to convert the linear displacement velocity array into a second linear displacement velocity array required by the mobile platform; adding the second linear displacement velocity array to the current pose of the mobile platform to generate an updated current pose during the iterative process; The inverse kinematics is calculated based on the updated current pose to obtain the current length of each passive elastic element during the iteration process; and the above actions are repeated to perform iterative update calculations until the length error value of each passive elastic element converges to a preset accurate value, at which point the calculation ends, and the updated current pose is output as the current pose of the mobile platform.

7. The passive six-axis parallel feedback control machine as claimed in claim 1, wherein the controller is configured to iteratively perform the following actions to achieve the action c): obtaining a linear thrust vector matrix of each of the passive elastic elements from each of the linear sensors; calculating a first coordinate position of each of the first joint elements in a base platform coordinate system and a second coordinate position of each of the second joint elements in the base platform coordinate system by inverse kinematics; calculating an Euclidean distance between each of the second joint elements and the corresponding line connecting them to the first joint elements based on the first and second coordinate positions; calculating a unit vector between each of the second joint elements and the corresponding line connecting them to the first joint elements based on the Euclidean distances; calculating an equivalent force of the moving platform relative to the external force based on the linear thrust vector matrix and the unit vector; calculating a line vector connecting a center position of the base platform and each of the second joint elements as a lever arm; and calculating an equivalent moment of the moving platform relative to the external force based on the lever arm and the equivalent force.

8. The passive six-axis parallel feedback control machine as claimed in claim 7, wherein the controller calculates the unit vector based on a first formula, calculates the equivalent force based on a second formula, and calculates the equivalent force moment based on a third formula, wherein the first formula is: , the second formula is: , and the third formula is: , where is the unit vector, is the Euclidean distance, F is the equivalent force, fi is the linear thrust vector matrix, T is the equivalent force moment, and is the connecting vector.

9. A compensation method for a passive six-axis parallel feedback control machine, applied to a passive six-axis parallel feedback control machine having a mobile platform, a base platform, a plurality of first joint elements respectively disposed on a first surface of the mobile platform, a plurality of second joint elements respectively disposed on a second surface of the base platform, six passive linear elastic elements disposed between the mobile platform and the base platform respectively through the plurality of first joint elements and the plurality of second joint elements, and a controller connected to the six passive linear elastic elements, wherein each passive linear elastic element has a passive elastic element and a linear sensor, the mobile platform has an initial pose determined by a free length of each passive elastic element, and the compensation method includes the following steps: Step a) When the mobile platform receives an external force, the linear sensor measures a compression amount of each passive elastic element, and the controller calculates a support force of each passive elastic element relative to the external force based on the compression amount; Step b) The controller calculates a positive kinematics based on the compression amount of each passive elastic element to obtain a current pose of the mobile platform; Step c) The controller calculates the equivalent force and equivalent moment of the moving platform relative to the external force based on the current pose and the support force of each of the passive elastic elements; Step d) The controller compares the initial pose and the current pose of the moving platform to obtain a displacement; and Step e) The controller generates a path compensation amount required for a transfer platform to cooperate with the passive six-axis parallel feedback control machine based on the equivalent force, the equivalent moment and the displacement.

10. The compensation method as claimed in claim 9, wherein each of the passive elastic elements has a stiffness coefficient, and step a) comprises: The controller calculates the compression amount based on the difference between the current length and the free length of each passive elastic element; and calculates the support force of each passive elastic element based on the compression amount and the stiffness coefficient of each passive elastic element according to Hooke's Law.

11. The compensation method as described in claim 9, further comprising: Step f) The controller determines, based on the displacement, whether at least one of the plurality of passive elastic elements is approaching or has reached a structural limit; and step g) When any of the passive elastic elements approaches or reaches the structural limit, a request command is issued to request the transfer platform to stop moving.

12. The compensation method as described in claim 9, wherein the transfer platform includes a host controller connected to the controller and receiving the path compensation amount, and a robotic arm connected to the host controller and disposed on the base platform, and further includes: Step h) The host controller adjusts a motion command based on the path compensation amount; and step i) The host controller controls the movement of the robotic arm based on the adjusted motion command, wherein the center point of the mobile platform remains in the initial pose when the robotic arm moves.

13. The compensation method as described in claim 9, wherein step b) comprises: Step b1) Obtain the current pose of the mobile platform and calculate an inverse kinematics based on the current pose to obtain the current length of each passive elastic element; Step b2) Calculate a length error value between the current length of each passive elastic element and a target length caused by the external force; Step b3) Calculate a linear displacement velocity array required for each passive elastic element based on the length error value and a time constant of an iterative algorithm; Step b4) Calculate a Jacobian matrix based on the current pose of the mobile platform and use the Jacobian matrix to convert the linear displacement velocity array into a second linear displacement velocity array required by the mobile platform; Step b5) Add the second linear displacement velocity array to the current pose of the mobile platform to generate an updated current pose during the iteration process; Step b6) Calculate the inverse kinematics based on the updated current pose to obtain the current length of each passive elastic element during the iteration process; and Step b7) The above steps are repeated for iterative update calculations until the length error value of each passive elastic element converges to a preset accurate value, at which point the calculation ends and the updated current pose is output as the current pose of the mobile platform.

14. The compensation method as described in claim 9, wherein step c) comprises: Step c1) Obtain a linear thrust vector matrix from each of the linear sensors for each of the passive elastic elements; Step c2) Calculate a first coordinate position for each of the first joint elements in a base platform coordinate system and a second coordinate position for each of the second joint elements in the base platform coordinate system using inverse kinematics; Step c3) Calculate an Euclidean distance between each of the second joint elements and the corresponding first joint elements based on the first and second coordinate positions; Step c4) Calculate a unit vector between each of the second joint elements and the corresponding first joint elements based on the Euclidean distances; Step c5) Calculate the equivalent force of the moving platform relative to the external force based on the linear thrust vector matrix and the unit vector; Step c6) Calculate the vector connecting a center position of the base platform and each of the second joint elements as a lever arm; and Step c7) Calculate the equivalent moment of the moving platform relative to the external force based on the lever arm and the equivalent force.

15. The compensation method as claimed in claim 14, wherein step c4) includes calculating the unit vector based on a first formula, step c5) includes calculating the equivalent force based on a second formula, and step c7) includes calculating the equivalent force moment based on a third formula, wherein the first formula is: , the second formula is: , and the third formula is: , where is the unit vector, is the Euclidean distance, F is the equivalent force, fi is the linear thrust vector matrix, T is the equivalent force moment, and is the connecting vector.

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