JP2008211872A - Linear motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a linear motor to correct a positioning error due to mechanical characteristics. <P>SOLUTION: The linear motor has a slider whose movement is linearly controlled in the direction of the axis of movement based on a given position command value. The linear motor includes: a data collecting means for measuring and collecting the roll angle, pitch angle, and yaw angle at every predetermined distance in the direction of the axis of movement; a functionalizing means for approximating change in roll angle, pitch angle, and yaw angle by a function based on collected data from the data collecting means; an integrating means for computing the vertical straightness and the horizontal straightness of the axis of movement based on the functions from the functionalizing means; and an absolute coordinate position computing means for computing the absolute coordinate position of the slider based on the position command value, the function data from the functionalizing means, and the data on vertical straightness and horizontal straightness from the integrating means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a linear motor having a slider whose movement is linearly controlled in a moving axis direction based on a given position command value.

  A lower-axis linear motor is formed by a pair of linear motors arranged in parallel, and a bridge-type motor in which an upper-axis linear motor is formed by bridging the sliders whose position is controlled in the axial direction of each lower-axis linear motor. The configuration of the XY stage and the position control of the slider are disclosed in Patent Document 1.

  FIG. 6 is a functional block diagram showing a general configuration of a linear motor arranged on a movement axis XX ′ parallel to the X axis. On a panel (not shown) horizontally installed on the stage, An embodiment in which a straight line L is drawn in the X-axis direction is shown.

  A linear motor 10 is disposed in the X-axis direction close to the upper surface of the panel, and a slider 11 whose position is controlled in the axial direction is mounted. Furthermore, the scale 12 is provided in the axial direction.

  The encoder 13 coupled to the slider 11 reads the scale 12, detects the movement distance of the slider 11, and outputs the X position detection value Px of the slider 11 based on the movement distance from the reference point.

  The driver 30 inputs the position command value Xcmd and the X position detection value Px from the host device 40, and supplies the current value M obtained by controlling and calculating the deviation to the motor winding of the lower shaft slider 11. 11 is controlled to move to the axis command value Xcmd.

  An ink jet device W is mounted on the slider 11 as a work 14, and a drawing line L is drawn on the liquid crystal panel by ink jet from the tip position (head position H) of the nozzle 15.

  FIG. 7 is a functional block diagram illustrating a configuration example of the driver 30. The driver 30 calculates a deviation between the position command value Xcmd and the position detection value Px and outputs a speed command value Vs, and calculates a deviation between the speed command value Vs and the speed detection value Vf to obtain a slider. 11 includes a speed control unit 32 that outputs a current value M to a difference detection unit 33 that outputs the speed detection value Vf based on a difference between the position detection value Px.

JP 2006-034078 A Robot Engineering Handbook -Robot Society of Japan- P196 First Edition: Oct. 20, 1990 Editor: Robotics Society of Japan Publisher: Corona Corporation

  In the position control system of the lower axis slider and the upper axis slider, the mechanical characteristics of the drive parts of the lower axis linear motor and the upper axis linear motor constituting the stage are not incorporated in the positioning control system, so that the accuracy of planar positioning However, there is a problem that it is affected by the mechanical characteristics of the stage.

The mechanical characteristics of the lower shaft and upper shaft are
(1) Characteristics due to minute rotation (roll, pitch, yaw) of driving part (2) Characteristics due to straightness (horizontal, vertical) of driving part (3) Characteristics due to thermal expansion of linear encoder (4) Lower shaft and upper The squareness of the axis.

  The present invention has been made to solve the above-described problems, and an object thereof is to realize a linear motor capable of correcting a positioning error based on mechanical characteristics.

In order to achieve such a subject, the present invention has the following configuration.
(1) In a linear motor having a slider whose movement is linearly controlled in the movement axis direction based on a given position command value,
Data collecting means for measuring and collecting a roll angle, a pitch angle, and a yaw angle for each predetermined distance in the moving axis direction;
Functionalizing means for approximating changes in roll angle, pitch angle, and yaw angle by a function based on the collected data of the data collecting means;
Integration calculating means for calculating the vertical straightness and horizontal straightness of the moving axis based on the function of the functionalizing means;
Absolute coordinate position calculating means for calculating the absolute coordinate position of the slider based on the position command value, the function data of the functionalizing means, and the vertical straightness and horizontal straightness data of the integral calculating means;
A linear motor comprising:

(2) The linear motor according to (1), wherein the absolute coordinate position calculation means includes a mathematical model of static characteristics using input data as a parameter.

(3) The absolute coordinate position calculation means inputs distance information from the slider to the work head position, and calculates the absolute coordinate position of the work head position. (1) or (2) Linear motor.

(4) The absolute coordinate position calculation means uses a position command value compensated for thermal expansion of the slider position detection encoder as a parameter of the mathematical model of the static characteristic (2) or (3) XY stage described in).

(5) Any one of (1) to (4), further comprising position command correction means for calculating a difference between an output of the absolute coordinate position calculation means and the position command value and correcting the position command value. The linear motor described in 1.

According to the present invention, the following effects can be expected.
(1) When a position command value is given, an actual slider position or head position based on the mechanical characteristics of the linear motor can be predicted. The position command value can be corrected by a correction value given by the difference between the predicted value and the position command value.

(2) A static characteristic mathematical model for predicting an actual slider position or head position based on the mechanical characteristics of a linear motor can be calculated by a well-known forward kinematic equation for analyzing the motion of a multi-degree-of-freedom joint. .

(3) By using the position command value compensated for the thermal expansion of the position detection encoder as a parameter of the mathematical model of the static characteristics, the head position compensated for the influence of the thermal expansion can be predicted.

  The present invention will be described in detail below with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of a linear motor to which the present invention is applied. The same elements as those of the conventional linear motor described with reference to FIGS. The embodiment of FIG. 1 is based on the assumption that the linear motor 10 is a rigid body that does not bend on its moving axis.

  Prior to the description of the embodiment, an actual slider position or head position moving process based on mechanical characteristics will be described. FIG. 2 is a schematic diagram showing the behavior of the slider based on the mechanical characteristics.

  In FIG. 2, the origin P of the absolute coordinate system (X_abs, Y_abs, Z_abs,) is defined at the start point of the encoder 3 of the linear motor. An origin Q of the relative coordinate system (X_inc, Y_inc, Z_inc) is defined on the slider 11.

  When the slider 11 located at the origin P of the absolute coordinate is controlled to move to the point S in the X axis direction by the position command value Xcmd, the origin Q of the relative coordinate is the horizontal straightness Y in the Y axis due to the mechanical characteristics of the S point. And the vertical straightness Z in the Z axis direction shifts in the Y direction and the Z direction due to the influence of the vertical straightness Z, and moves to the Q point position shown in the figure. This Q point is the predicted position of the slider 11.

  Furthermore, a position H to which distance information (X_inc, Y_inc, Z_inc) from the Q point to the working head is added is a predicted head position. A difference between the predicted head position information and the position command value Xcmd position information is a position control error based on mechanical characteristics.

  Returning to FIG. 1, the embodiment will be described. The data collecting means 100 measures and collects roll angles φ1, φ2,... Φn, pitch angles θ1, θ2,... Θn, and yaw angles ψ1, ψ2,.

  FIG. 3 is a plan view showing an embodiment of data collection. A linear motor 10 arranged in parallel in the X-axis direction and a laser head 50 that emits a laser beam in the X-axis direction are fixedly arranged on the moving axis.

  The slider 11 arranged at the initial position of the absolute coordinate origin (point P in FIG. 2) is opposed to the laser head 50 on the moving axis, reflects the beam BM by the reflecting mirror 60 mounted on the slider, and the laser head. Return to 50.

  The roll angle φ1, pitch angle θ1, and yaw angle ψ1 of the linear motor 10 as a rigid body at the reflection position can be measured by the interferometer 70 through which the outgoing beam and reflected beam of the beam BM pass. By performing the same measurement n times while moving the slider 11 on the linear motor 10 by a predetermined distance in the direction away from the laser head 50, the data collecting means 100 can collect data.

  The functionalizing means 200 approximates the change in the roll angle φ data collected by the data collecting means 100 with a function φ (X). Similarly, a change in pitch angle θ data is approximated by a function θ (X). Similarly, a change in yaw angle ψ data is approximated by a function ψ (X).

  The integral calculation means 300 calculates the vertical straightness Z (X) and the horizontal straightness Y (X) by integrating the functions θ (X) and ψ (X) of the functionalizing means.

  FIG. 4 is a characteristic diagram showing the horizontal and vertical straightness obtained by the collected data, function approximation, and integral calculation. (A) shows collected data and function approximation characteristics, (A) shows changes in yaw data ψ and approximation function ψ (X), and (B) shows changes in pitch data θ and approximation function θ (X).

  FIG. 4B shows the function characteristics of the integration calculation result, (A) shows the horizontal straightness Y (X) obtained by integrating the approximation function ψ (X) of the yaw data, and (B) shows the approximation function of the pitch data. The vertical straightness Z (X) obtained by integrating θ (X) is shown.

  The absolute coordinate position calculating means 400 predicts and calculates the absolute coordinate position of the slider 11 based on the position command value Xcmd, the function data of the functionalizing means 200, and the vertical straightness and horizontal straightness data of the integral calculating means 300.

  The absolute coordinate position calculation means 400 receives distance information from the slider 11 to the work head H according to user settings from the head position setting means 500, and predicts and outputs the absolute coordinate position Xabs of the work head H.

The subtractor 600 outputs a correction value e obtained by subtracting the position command value Xcmd from the predicted position Xabs output from the absolute coordinate position calculation unit 400 to the position command correction unit 700. The position command correction means 700 is a position command value obtained by subtracting the correction value e from the position command value Xcmd.
Xcmd ′ (= 2Xcmd−Xabs) is passed to the lower axis driver 30.

  The absolute coordinate position calculation means 400 includes a mathematical model 401 of static characteristics using input data as a parameter. As a mathematical model of this static characteristic, a forward kinematic equation well known in robotics can be used.

  Non-Patent Document 1 describes the forward kinematic equation. Direct kinematics is a problem of obtaining the position, posture, velocity, acceleration, angular velocity, and angular acceleration of each link when given joint position, velocity, and acceleration. In particular, the problem of obtaining the position, posture, velocity, and angular velocity of the end link, that is, the end effector is important in practice. Forward kinematics is abbreviated as DK. As a method for analyzing forward kinematics, a method using simultaneous conversion and a method using vectors are known.

  A mathematical model 401 of the linear motor static characteristics based on the forward kinematic equation is shown in the following equation.

  By solving equation (1), the expected position (Xabs, Yabs, Zabs) of the work head H viewed from the origin P of absolute coordinates can be calculated.

  The position command value that is a parameter of the mathematical model 401 of the static characteristics of the absolute coordinate position calculation means is set to a command value that takes into account the thermal expansion of the encoder 13, so that the work head H that reflects the influence of the thermal expansion of the encoder 13 is reflected. Expected positions (Xabs, Yabs, Zabs) can be calculated.

The lower shaft position command value Xcmd1 considering the thermal expansion of the encoder is given by the following equation. The same applies to the position command value of the upper shaft.
Xcmd = {1 + γ (Tx−To)} xcmd (2)
Where To: reference temperature of the encoder
Tx: Encoder current temperature xcmd: Driver internal command value Xcmd: Command value after temperature compensation
γ: Thermal expansion coefficient of the glass scale that composes the encoder

  FIG. 5 is a position error characteristic diagram of a linear motor to which the present invention is applied. G1 indicates the transition of the position error when the correction is not performed according to the present invention, and increases proportionally as the slider moves away from the origin position, and reaches 20 micrometers or more at the end of the span.

  G2 shows the transition of the position error when the correction according to the present invention is executed, and the error between the actual measurement value and the predicted value over the entire moving span of the slider is within a few micrometers, and according to the present invention. The correction effect can be confirmed.

It is a functional block diagram which shows one Embodiment of the linear motor to which this invention is applied. It is a schematic diagram which shows the behavior of the slider based on a mechanical characteristic. It is a top view which shows embodiment of data collection. It is a characteristic view which shows the horizontal and vertical straightness by collection data, function approximation, and integral calculation. It is a position error characteristic view of a linear motor to which the present invention is applied. It is a functional block diagram which shows the general structure of a linear motor. It is a functional block diagram which shows the structural example of a driver.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Slider 13 Encoder 30 Driver 31 Position control part 32 Speed control part 33 Difference calculation means 40 Host apparatus 100 Data collection means 200 Functionalization means 300 Integration calculation means 400 Absolute position calculation means 500 Head position setting means 600 Subtractor 700 Position command correction means

Claims (5)

In a linear motor having a slider that is linearly controlled to move in the movement axis direction based on a given position command value,
Data collecting means for measuring and collecting a roll angle, a pitch angle, and a yaw angle for each predetermined distance in the moving axis direction;
Functionalizing means for approximating changes in roll angle, pitch angle, and yaw angle by a function based on the collected data of the data collecting means;
Integration calculating means for calculating the vertical straightness and horizontal straightness of the moving axis based on the function of the functionalizing means;
Absolute coordinate position calculating means for calculating the absolute coordinate position of the slider based on the position command value, the function data of the functionalizing means, and the vertical straightness and horizontal straightness data of the integral calculating means;
A linear motor comprising:   The linear motor according to claim 1, wherein the absolute coordinate position calculation means includes a mathematical model of static characteristics using input data as a parameter.   3. The linear motor according to claim 1, wherein the absolute coordinate position calculation means inputs distance information from the slider to a work head position and calculates an absolute coordinate position of the work head position.   4. The XY according to claim 2, wherein the absolute coordinate position calculation means uses a position command value compensated for thermal expansion of the slider position detection encoder as a parameter of the mathematical model of the static characteristic. 5. stage.   5. The linear motor according to claim 1, further comprising a position command correction unit that calculates a difference between an output of the absolute coordinate position calculation unit and the position command value and corrects the position command value. .

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