JP3636952B2 - Numerical controller - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a numerical controller for controlling a parallel mechanism machine tool.
[0002]
[Prior art]
The six legs arranged in parallel are connected to the movable member with a ball joint, the length of the leg from the fixed member is controlled to adjust the tilt and position of the movable member, and the work is performed with the machining head attached to the movable member. A machine tool that applies a so-called parallel mechanism is known. Such machine tools are described in detail in “GEODETICS HEXAPOD” (by Nakano Masatake), “Machine and Tools” published by the Industrial Research Council, February 1995 issue. The detailed description of is omitted.
[0003]
In an apparatus for numerically controlling a machine tool to which such a parallel mechanism is applied, the position and posture of a movable member are controlled in accordance with a command given in an orthogonal coordinate system (hereinafter referred to as a Cartesian coordinate system). This control will be described by taking a machine tool to which a parallel mechanism as shown in FIG. 2 is applied as an example. The machine tool shown in FIG. 2 includes a fixed member 21, a movable member 22, six first joints 23 attached to the fixed member 21, and six second joints 24 attached to the movable member 22. And six legs 25, and a driving device 26 provided for each leg adjacent to the joint 23 on the fixing member side.
[0004]
In this machine tool, the legs 25 pass through the six joints 23 of the fixed member 21, and the legs 25 are attached to the six joints 24 of the movable member 22. In addition, a driving device 26 is attached to each leg 25, so that a fulcrum of the fixed member 21, which is a connection point between the fixed member 21 and the leg 25, and a connection point between the movable member 22 and the leg 25. The distance from the fulcrum of a certain movable member 22 (hereinafter referred to as leg length) can be increased or decreased.
[0005]
By the way, in order to control the position and posture of the movable member 22, first, the coordinates of each fulcrum of the movable member 22 with respect to the desired position and posture of the movable member 22 are obtained based on the coordinates of the machining locus, and from this, each leg 25. The length of will be calculated. Since the coordinates of each fulcrum of the fixed member 21 are fixed, the length of each leg 25 can be obtained from the coordinates of each fulcrum of the movable member 22. And the movable member 22 is controlled to a desired position and attitude | position by controlling the drive device 26 so that it may become the length of the leg 25 calculated | required here. Thus, in the parallel mechanism machine tool, control is performed by the coordinates of the fulcrum of the fixed member 21 and the movable member 22.
[0006]
FIG. 3 is a block diagram showing an example of a numerical controller of a conventional parallel mechanism machine tool. As shown in FIG. 3, a conventional numerical control device for a parallel mechanism machine tool includes a program interpretation unit 1, an interpolation coordinate calculation unit 2, a mechanism parameter storage unit 3, an inverse mechanism conversion unit 7 ', and a drive device control. Part 8.
[0007]
Hereinafter, the operation of each unit will be described. The program interpretation unit 1 interprets the machining program block by block and generates block information BI. The interpolation coordinate calculation unit 2 obtains the interpolation position CP of the machining locus in Cartesian coordinates from the block information BI. The mechanism parameter storage unit 3 stores design mechanism parameters (hereinafter referred to as ideal mechanism parameters). Here, the mechanism parameter indicates the absolute coordinates of each fulcrum of the fixed member 21 and the relative coordinates of each fulcrum of the movable member 22 with the processing position (for example, the blade edge position) as the origin . The reverse mechanism conversion unit 7 ′ converts the interpolation position CP in Cartesian coordinates into the leg length LP using the ideal mechanism parameter IP. The drive device controller 8 drives the drive device attached to the legs according to the length LP of each leg.
[0008]
[Problems to be solved by the invention]
As described above, in the conventional numerical control device, the inverse mechanism conversion unit 7 ′ converts the interpolation position CP in Cartesian coordinates into the leg length LP using the ideal mechanism parameter IP. Because the fulcrum of the fixed member and the fulcrum of the movable member deviate from the ideal mechanism parameter IP due to manufacturing errors of the machine tool itself, an accurate leg length cannot be obtained, and the actual cutting edge position is There was a problem that a trajectory error occurred due to deviation from the command given in Cartesian coordinates.
[0009]
Specifically, a manufacturing error of the machine tool occurs in the joint portion (first joint 23) between the fixed member 21 and the leg 25 and the joint portion (second joint 24) between the movable member 22 and the leg 25. The fulcrum on the fixed member side and the fulcrum on the movable member side vary from the ideal fulcrum. As an example, the manner in which the fulcrum on the side of the fixing member 21 deviates from the ideal mechanism parameter will be described with reference to an example of the specific shape of the first joint 23 that joins the fixing member and the leg as shown in FIG. . The first joint 23 includes a first rotation shaft 41, a first support member 42, a second rotation shaft 43, and a second support member 44, and has a cylindrical first rotation shaft. 41 is attached to the fixing member 21, and a cylindrical first support member 42 is fixed to the first rotating shaft 41. A cylindrical second rotation shaft 43 is attached to the inside of the first support member 42, and a cylindrical second support member 44 is fixed to the second rotation shaft 43. Further, the leg 25 is attached to the second support member 44 so as to penetrate therethrough, and the first rotating shaft 41 and the second rotating shaft 43 can freely rotate to arbitrarily change the direction of the leg. ing. Ideally, the first rotating shaft 41, the second rotating shaft 43, and the leg intersect at one point, and this point is a fulcrum of the fixing member. At this time, the coordinates of the fulcrum of the fixed member are fixed even if the direction of the leg changes with the change of the position and posture of the movable member. However, due to manufacturing errors, the first rotary shaft 41, the second rotary shaft 43, and the legs 25 are attached to the fixed member, the first support member 42, and the second support member 44, respectively, in a shifted manner. It has been. For this reason, the fulcrum on the fixing member side does not normally move along the second rotating shaft 43, but moves around the second rotating shaft 43 as the leg direction changes and the second rotating shaft 43 rotates. Moving. Similarly, when the first rotating shaft 41 is rotated, the first rotating shaft 41 moves along with the first rotating shaft 41. Thus, the actual coordinates of the fulcrum of the fixing member are not fixed and deviate from the ideal mechanism parameter IP.
[0010]
The fact that the actual fulcrum on the movable member side deviates from the ideal parameter IP will be described with reference to an example of the second joint 24 that couples the movable member and the leg as shown in FIG. The second joint 24 shown in FIG. 5 includes a third rotating shaft 51, a third supporting member 52, a fourth rotating shaft 53, a fourth supporting member 54, and a fifth rotating shaft 55. It is composed of A cylindrical third rotation shaft 51 is attached to the movable member 22, and a U-shaped third support member 52 is fixed to the third rotation shaft 51. A columnar fourth rotation shaft 53 is attached to the inside of the third support member 52, and a fourth support member 54 is fixed to the fourth rotation shaft 53. A columnar fifth rotation shaft 55 is attached to the fourth support member 54. A leg 25 is attached to the fifth rotating shaft, and the third rotating shaft 51, the fourth rotating shaft 53, and the fifth rotating shaft 55 rotate so that the direction of the leg 25 can be arbitrarily changed. It has become. Ideally, the fourth support member 54, the fifth rotation shaft 55, and the leg 25 are on the same straight line, and the third rotation shaft 51, the fourth rotation shaft 53, and the leg 25 intersect at one point. This is a fulcrum on the movable member side. At this time, the relative coordinates of the fulcrum on the movable member side are fixed even if the direction of the leg changes with the change in the position and posture of the movable member. However, due to manufacturing errors, the third rotating shaft 51, the fourth rotating shaft 53, the fifth rotating shaft 55, and the leg 25 are respectively movable member 22, third rotating shaft 51, and fourth rotating shaft. The rotary shaft 53 and the fifth rotary shaft 55 are attached with a shift. For this reason, the fulcrum on the movable member side is not usually located on the fourth rotating shaft 53, and when the direction of the leg 25 changes and the fourth rotating shaft 53 rotates, the fourth rotating shaft 53 rotates accordingly. Move around. Similarly, when the third rotating shaft 51 rotates, not normally along the first rotating shaft 51, the third rotating shaft 51 is moved accordingly. Thus, the actual coordinates of the fulcrum of the movable member are not fixed and deviate from ideal mechanism parameters.
[0011]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a numerical control device capable of improving machining accuracy by obtaining the length of each leg in consideration of manufacturing errors.
[0012]
[Means for Solving the Problems]
The present invention for solving the problems of the conventional example includes a parallel mechanism machine tool having a fixed member, and a movable member supported by a plurality of variable length legs extending from the fixed member and to which a processing tool is attached. wherein, according to a machining program, the interpolation position on the machining trajectory calculated, the interpolation position, the absolute coordinates of the fulcrum of the fixed member is the point of attachment of the fixed member and the variable-length legs, the point of attachment of the movable member and the variable-length legs a numerical controller of the fulcrum of the movable member, is converted to the length of the legs by using the kinematic parameters consisting of a relative coordinate whose origin the machining point of the machining tool for controlling the parallel kinematic mechanism machine tool is, the fulcrum means for storing static position error information relating to, the direction of each variable-length leg of the interpolation position, means for calculating with the ideal kinematic parameters, the variable length legs The position error of each fulcrum is changed by the direction of the change, that the said the direction of the variable-length legs is calculated based on the static position error information of the respective support point, and means for correcting the kinematic parameters based on the calculation result It is characterized by.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a numerical control device for a parallel mechanism machine tool according to an embodiment of the present invention. As shown in FIG. 1, the numerical controller of the parallel mechanism machine tool according to the present embodiment includes a program interpretation unit 1, an interpolation coordinate calculation unit 2, a mechanism parameter storage unit 3, a leg direction calculation unit 4, It comprises a static error (fulcrum position error) information storage unit 5, a mechanism parameter correction unit 6, a reverse mechanism conversion unit 7, and a drive device control unit 8. Here, the program interpretation unit 1, the interpolation coordinate calculation unit 2, the mechanism parameter storage unit 3, and the drive device control unit 8 are the same as those in FIG. 3 showing a conventional numerical control device of a parallel mechanism machine tool. Therefore, detailed description is omitted. The interpolation coordinate calculation unit 2 calculates the interpolation position, the leg direction calculation unit 4 calculates the leg direction, and the static error information storage unit 5 stores the fulcrum position error information of each leg. Further, the mechanism parameter correction unit 6 corresponds to means for correcting the mechanism parameter, and the reverse mechanism conversion unit 7 corresponds to means for converting the interpolation position into the leg length.
[0014]
The leg direction calculation unit 4 uses the interpolation coordinates CP in Cartesian coordinates output from the interpolation coordinate calculation unit 2 and the ideal mechanism parameter IP stored in the mechanism parameter storage unit 3 to determine the direction of each leg 25. LD (vector representing the direction of each leg 25) is output.
[0015]
The static error information storage unit 5 stores static error information PE regarding the fulcrum on the fixed member 21 side and the fulcrum on the movable member 22 side. Here, as static error information of the fulcrum on the fixing member 21 side, when the rotation angles of the first rotation shaft 41 and the second rotation shaft 43 of the joint 23 on the fixing member 21 side are both 0, There are coordinates of the fulcrum on the fixing member 21 side, position information of the first rotating shaft 41, and position information of the second rotating shaft 43. Regarding the fulcrum on the movable member 22 side, the intersection of the fourth rotation shaft 53 and the fourth support member 54 has been described as a fulcrum, but in reality, the fourth support member 54 ahead of the fourth rotation shaft 53, Since an error in manufacturing also occurs in the fifth rotating shaft 55 and the leg 25, an accurate leg length is obtained by using the coupling point of the fifth rotating shaft 55 and the leg 25 as a fulcrum on the movable member 22 side. It is preferable to obtain it. Accordingly, as static error information of the fulcrum on the movable member 22 side, the rotation of the third rotating shaft 51, the fourth rotating shaft 53, and the fifth rotating shaft 55 of the joint 24 attached to the movable member 22 is performed. The coordinates of the fulcrum on the movable member 22 side, the position information of the fifth rotating shaft 55, the position information of the fourth rotating shaft 53, and the position information of the third rotating shaft 51 when the angles are all 0. There is. Here, the position where the rotation angle of each rotating shaft becomes 0 may be determined appropriately. Position information of each axis of rotation, for example, be expressed by a direction vector of the coordinates of a point on the axis of the rotary shaft and the axis.
[0016]
The mechanism parameter correction unit 6 obtains an actual mechanism parameter RP based on the static error information PE and the direction LD of each leg . Request fulcrum of actual fixing member as follows. As described above, the leg direction calculation unit 4 uses the interpolation coordinates CP obtained by interpreting the machining program and the ideal mechanism parameter IP so that the machining positions coincide with the interpolation coordinates CP. Absolute coordinates are obtained, and the direction of each leg 25 is calculated from the absolute coordinates. The angle at which the leg direction changes with respect to the reference direction (rotation angle 0) when the static error information is obtained is calculated. Since the fulcrum of the fixing member has two rotation axes as shown in FIG. 4, the change in the direction of the leg can be expressed as a rotation angle around each axis of the two rotation axes. The rotation angle around the axis of the rotation shaft 41 is α, and the rotation angle around the axis of the second rotation shaft 43 is β. Further, the rotation angle about the first axis of rotation 41 is A1, the rotation angle about the second axis of rotation 43 is referred to as the (A1, A2) that is A2. The coordinates of the fulcrum on the stationary member 21 side of the static error information PE are rotated by β around the axis stored as the position information of the second rotation shaft 43 of the static error information PE, and (0, The coordinates of the fulcrum on the fixing member 22 side in the case of β) are obtained. The coordinates of the fulcrum on the fixed member 21 side at (0, β) are rotated by α around the axis stored as the position information of the first rotating shaft 41 of the static error information PE, and ( The coordinates of the fulcrum on the fixing member 21 side at the time of α, β) are obtained. That is, the coordinate difference of the fulcrum position measured at the time of (0, 0) as the static error information PE is set around each axis based on the leg direction LD calculated using ideal mechanism parameters. The coordinates of the actual fulcrum of the fixing member 21 can be obtained by rotating each by (α, β).
[0017]
Next, the actual fulcrum of the movable member is obtained in the same manner. That is, the angle at which each leg direction LD based on the ideal mechanism parameter IP and the interpolation position CP is changed from the reference direction when the static error position information is obtained is calculated. Since the fulcrum of the movable member has three rotation axes as shown in FIG. 5, the change in the direction of the leg can be expressed as a rotation angle around each axis of these rotation axes. Rotation angle around the axis of 51 is γ, rotation angle around the axis of the fourth rotation shaft 53 is δ, and rotation angle around the axis of the fifth rotation shaft 55 is ε. Moreover, indicating that the rotation angle about the third rotation shaft 51 is A3, the rotational angle about the fourth rotation shaft 53 is A4, the rotation angle for the fifth rotation shaft 55 is A5 with (A3, A4, A5) . The coordinates of the fulcrum of the movable member 22 of the static error information PE are rotated by ε around the axis stored as the position information of the fifth rotating shaft 55 of the static error information PE, and (0, 0 , Ε), the coordinates of the fulcrum of the movable member 22 are obtained. The coordinates of the fulcrum of the movable member 22 at the time of (0, 0, ε) are rotated by δ around the axis stored as the position information of the fourth rotating shaft 53 of the static error information PE, The coordinates of the fulcrum of the movable member 22 at (0, δ, ε) are obtained. The coordinate of the fulcrum of the movable member 22 at the time of (0, δ, ε) is rotated by γ around the axis stored as the position information of the third rotating shaft 51 of the static error information PE, The coordinates of the fulcrum of the movable member 22 when (γ, δ, ε), that is, the coordinates of the actual fulcrum of the movable member 22 are obtained. In this way, the coordinates of each fulcrum considering the error are obtained. As described above, since the mechanism parameter is determined by the coordinates of each fulcrum, the mechanism parameter obtained from the coordinates of each fulcrum considering this error is a mechanism parameter considering the error. In this way, the actual mechanism parameter RP is obtained by correcting the ideal mechanism parameter.
[0018]
The reverse mechanism conversion unit 7 converts the interpolation position CP in Cartesian coordinates into the length LP of the leg 25 using the actual mechanism parameter RP.
[0019]
Here, the leg direction calculation unit 4 obtains the leg direction by calculation, but the direction of each leg 25 may actually be measured using a sensor or the like.
[0020]
【The invention's effect】
As described above, according to the numerical controller of the parallel mechanism machine tool of the present invention, the mechanism parameters are corrected in consideration of the manufacturing error of the machine tool, so that the accurate leg length can be obtained. , Processing accuracy can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a configuration in the present invention.
FIG. 2 is an explanatory view showing an example of a machine tool to which a parallel mechanism is applied.
FIG. 3 is a block diagram illustrating an example of a configuration in a conventional technique.
FIG. 4 is an explanatory view showing an example of a joint for joining a fixing member and a leg.
FIG. 5 is an explanatory view showing an example of a joint for joining a movable member and a leg.
[Explanation of symbols]
1 program interpretation unit, 2 interpolation coordinate calculation unit, 3 mechanism parameter storage unit, 4 leg direction calculation unit, 5 static error information storage unit, 6 mechanism parameter correction unit, 7 reverse mechanism conversion unit, 8 drive device control unit, 21 Fixed member, 22 Movable member, 23 1st joint, 24 2nd joint, 25 legs, 26 Drive device, 41 1st rotating shaft, 42 1st support member, 43 2nd rotating shaft, 44 2nd Support member, 51 3rd rotating shaft, 52 3rd supporting member, 53 4th rotating shaft, 54 4th supporting member, 55 5th rotating shaft.

Claims (1)

A fixing member;
A parallel mechanism machine tool having a movable member supported by a plurality of variable length legs extending from the fixed member and to which a machining tool is attached;
According to the machining program, the interpolation position on the machining trajectory is calculated, and this interpolation position is the absolute coordinates of the fulcrum of the fixed member, which is the coupling point between the fixed member and the variable length leg, and the coupling point between the movable member and the variable length leg. In a numerical control device for controlling the parallel mechanism machine tool by converting the length of a leg using a mechanism parameter composed of a relative coordinate with a processing point of a processing tool of a fulcrum of a movable member as an origin ,
Means for storing static position error information relating to the fulcrum ;
Means for calculating the direction of each variable length leg at the interpolation position using ideal mechanism parameters;
Means for calculating a position error of each fulcrum that changes due to a change in the direction of the variable length leg based on the direction of the variable length leg and the static position error information, and correcting a mechanism parameter based on the calculation result ;
A numerical control device comprising:

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