Six-axis parallel robot capable of measuring and measuring method for using the same

Abstract

A six-axis parallel robot includes a mobile platform, a base platform, and six actuators connected between the mobile platform and the base platform via multiple joints. The mobile platform has a target pose and multiple resistive forces. Each actuator has a linear motor and a driver, wherein each driver performs the following actions: reading the current value of each linear motor when subjected to an external force less than or equal to a threshold; performing compliant motion and reading the displacement change of each linear motor when subjected to an external force greater than the threshold; calculating the positive kinematics based on the displacement change to obtain the current pose of the mobile platform; calculating the equivalent force and equivalent torque of the mobile platform relative to the external force based on the current value and the current pose; and comparing the current pose with the target pose to calculate the displacement and angular change of the mobile platform.

Claims

1. A six-axis parallel robot with measurement 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; A plurality of second joint elements are respectively disposed on the second surface; and six linear actuators are respectively disposed between the moving platform and the base platform through the plurality of first joint elements and the plurality of second joint elements, and each linear actuator has a linear motor and a motor driver, wherein the moving platform has a target pose and a plurality of resistance forces relative to a plurality of directions, and each motor driver is configured to perform the following actions: Action a) Controlling the operation of each linear motor based on a motion command to provide a thrust so that the moving platform maintains the target pose; Action b) When the moving platform receives an external force and the external force is less than or equal to a thrust threshold, reading a current value of each linear motor and calculating a current change; Action c) When the moving platform receives the external force and the external force is greater than the thrust threshold, controlling each linear actuator to perform compliant movement and reading a linear displacement change of each linear motor; Action d) Calculating a positive kinematics based on the linear displacement change of each linear motor to obtain a current pose of the moving platform; Action e) Calculate the equivalent force and equivalent moment of the moving platform relative to the external force based on the current change of each linear motor and the current pose; and action f) Compare the current pose and the target pose to calculate a displacement and an angle change of the moving platform.

2. The six-axis parallel robot as claimed in claim 1, wherein each of the motor drivers is further configured to perform the following actions respectively: action a01) receiving an external operation to set the target pose of the mobile platform and generating a motion command for controlling each of the linear motors based on the target pose; and action a02) receiving the external operation to set the plurality of resistance forces of the mobile platform relative to a plurality of directions and setting a thrust threshold based on the plurality of resistance forces, wherein the plurality of resistance forces include three-axis forces and three-axis torques in a cassette coordinate system.

3. The six-axis parallel robot as claimed in claim 2, wherein in the action a01), each of the motor drivers is configured to perform an inverse kinematics calculation based on the target pose to obtain a linear displacement that each linear actuator needs to follow to maintain the mobile platform in the target pose, and to generate the corresponding motion command based on the linear displacement.

4. The six-axis parallel robot as claimed in claim 3, wherein each of the motor drivers is further configured to perform the following actions to calculate the linear displacement of each of the linear actuators: inputting the target pose of the mobile platform relative to a base platform coordinate system, a first distance between a center point of the mobile platform and each of the first joint elements, a second distance between a center point of the base platform and each of the second joint elements, a first angle representing half the angle between two closer first joint elements on the mobile platform, and a second angle representing half the angle between two closer second joint elements on the base platform; calculating a second coordinate position of each of the second joint elements in the base platform coordinate system based on the second distance and the second angle; Based on the first distance and the first included angle, calculate a first coordinate position of each of the first joint elements in the coordinate system of the base platform; and based on the target pose of the mobile platform with the coordinate system of the base platform as a reference, sequentially perform a coordinate transformation matrix multiplication on the first coordinate position of each of the first joint elements, and take Euclidean distance with the corresponding second joint elements to obtain the linear displacement of the corresponding linear actuator.

5. The six-axis parallel robot as claimed in claim 1, wherein each of the motor drivers is further configured to iteratively perform the following actions to achieve action d): obtaining the current pose of the mobile platform and performing an inverse kinematics calculation based on the current pose to obtain a current linear displacement of each of the linear motors; calculating the current linear displacement of each of the linear motors and a displacement error value of a target linear displacement caused by the external force; calculating a linear displacement velocity array required by each of the linear actuators based on the displacement 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 calculation is performed based on the updated current pose to obtain the current linear displacement of each linear motor during the iteration process; and the above actions are repeated to perform iterative update calculations until the displacement error value of each linear motor 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.

6. The six-axis parallel robot as claimed in claim 1, wherein each of the motor drivers is further configured to iteratively perform the following actions to achieve the action e): obtaining a plurality of linear thrust vector matrices from the linear actuators, wherein each linear thrust vector matrix is ​​directly related to the change in current; calculating, through inverse kinematics, a first coordinate position of each first joint element represented in a base platform coordinate system, and a second coordinate position of each second joint element represented in the base platform coordinate system, to obtain a plurality of first coordinate positions and a plurality of second coordinate positions; calculating, based on the first coordinate positions and the second coordinate positions, a Euclidean distance between each second joint element and the corresponding first joint element, to obtain a plurality of Euclidean distances; calculating, based on the Euclidean distances, a unit vector between each second joint element and the corresponding first joint element, to obtain a plurality of unit vectors; and calculating, based on the linear thrust vector matrices and the unit vectors, the equivalent force of the moving platform relative to the external force; Calculate a line vector connecting a center position of the base platform to each of the second joint elements as a lever arm; and calculate an equivalent moment of the moving platform relative to the external force based on the lever arm and the equivalent moment.

7. The six-axis parallel robot as claimed in claim 6, wherein each of the motor drivers calculates the unit vector based on a first formula, the equivalent force based on a second formula, and 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.

8. A measurement method for a six-axis parallel robot, applied to a six-axis parallel robot 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, and six linear actuators respectively disposed between the mobile platform and the base platform through the plurality of first joint elements and the plurality of second joint elements, wherein the mobile platform has a target pose and a plurality of resistance forces relative to a plurality of directions, each of the linear actuators has a linear motor and a motor driver, and the measurement method includes the following steps: Step a) Each motor driver controls the operation of each linear motor based on a motion command to provide a thrust so that the mobile platform maintains the target pose; Step b) When the mobile platform receives an external force and the external force is less than or equal to a thrust threshold, each motor driver reads a current value of each linear motor and calculates a current change; Step c) When the mobile platform receives the external force and the external force is greater than the thrust threshold, each motor driver controls each linear actuator to perform compliant movement and reads the linear displacement change of each linear motor; Step d) Each motor driver calculates a positive kinematics based on the linear displacement change of each linear motor to obtain a current pose of the mobile platform; Step e) Each motor driver calculates an equivalent force and an equivalent moment of the mobile platform relative to the external force based on the current change of each linear motor and the current pose; and Step f) Each motor driver compares the current pose and the target pose to calculate a displacement and an angle change of the mobile platform.

9. The measurement method as described in claim 8, further comprising: Step a01) Receive an external operation to set the target pose of the mobile platform and generate the motion command for controlling each of the linear motors based on the target pose; and Step a02) Receive the external operation to set the multiple resistance forces of the mobile platform relative to multiple directions and set the thrust threshold based on the multiple resistance forces, wherein the multiple resistance forces include triaxial forces and triaxial torques in the cassette coordinate system.

10. The measurement method as claimed in claim 9, wherein step a01) includes each of the motor drivers performing an inverse kinematics calculation based on the target pose to obtain a linear displacement that each linear actuator needs to follow to maintain the moving platform in the target pose, and generating a corresponding motion command based on the linear displacement.

11. The measurement method as described in claim 10, wherein step a01) further comprises: Step a011) Input the target pose of the mobile platform based on a base platform coordinate system, a first distance between a center point of the mobile platform and each of the first joint elements, a second distance between a center point of the base platform and each of the second joint elements, a first included angle representing half the included angle between two closest first joint elements on the mobile platform, and a second included angle representing half the included angle between two closest second joint elements on the base platform; Step a012) Calculate a second coordinate position of each of the second joint elements in the base platform coordinate system based on the second distance and the second included angle; Step a013) Calculate a first coordinate position of each of the first joint elements in the base platform coordinate system based on the first distance and the first included angle; and Step a014) Based on the target pose of the mobile platform with the coordinate system of the base platform as a reference, a coordinate transformation matrix multiplication is performed sequentially on the first coordinate position of each first joint element, and Euclidean distance is taken with the corresponding second joint element to obtain the linear displacement of each corresponding linear actuator.

12. The measurement method as described in claim 8, wherein step d) comprises: Step d1) Obtain the current pose of the mobile platform and perform an inverse kinematics calculation based on the current pose to obtain the current linear displacement of each linear motor; Step d2) Calculate the current linear displacement of each linear motor and a displacement error value of a target linear displacement caused by the external force; Step d3) Calculate a linear displacement velocity array required by each linear actuator based on the displacement error value and a time constant of an iterative algorithm; Step d4) 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 d5) 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 d6) Perform the inverse kinematics calculation based on the updated current pose to obtain the current linear displacement of each linear motor during the iteration process; and Step d7) The above actions are repeated to perform iterative update calculations until the displacement error value of each linear motor 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.

13. The measurement method as described in claim 8, wherein step e) comprises: Step e1) Obtain multiple linear thrust vector matrices from the linear actuators, where each linear thrust vector matrix is ​​directly related to the current change; Step e2) Calculate a first coordinate position for each first joint element in a base platform coordinate system and a second coordinate position for each second joint element in the same system using inverse kinematics to obtain multiple first coordinate positions and multiple second coordinate positions; Step e3) Calculate an Euclidean distance between each second joint element and its corresponding first joint element based on the first and second coordinate positions to obtain multiple Euclidean distances; Step e4) Calculate a unit vector between each second joint element and its corresponding first joint element based on the Euclidean distances to obtain multiple unit vectors; Step e5) Calculate the equivalent force of the moving platform relative to the external force based on the linear thrust vector matrices and the unit vectors; Step e6) Calculate a line vector connecting the center position of the base platform and each of the second joint elements as a lever arm; and step e7) calculate an equivalent moment of the moving platform relative to the external force based on the lever arm and the equivalent moment.

14. The measurement method as claimed in claim 13, wherein step e4) includes calculating the unit vector based on a first formula, step e5) includes calculating the equivalent force based on a second formula, and step e7) 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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