Stylus attitude determination method and stylus attitude determination device

Abstract

The present invention comprises: a repetitive control unit (140) that causes units from an evaluation point setting unit (126) to a moment calculation unit (138) to operate repeatedly at a plurality of rotation angle positions of a stylus model (26M) while rotating the stylus model (26M) around a rotation axis (C); and an optimal attitude determination unit (142) that determines an optimal attitude of a stylus (26) in a direction around the rotation axis (C) on the basis of the calculation results of the moment calculation unit (138) for each rotation angle position. Units from an initial setting unit (124) to the optimal attitude determination unit (142) are made to operate repeatedly for each of a plurality of measurement path positions (On) on a measurement path (202).

Description

Stylus attitude determination method and stylus attitude determination device

[0001] The present invention relates to a stylus attitude determination method and a stylus attitude determination device for determining the attitude of a stylus for each of a plurality of positions on a measurement path.

[0002] Conventionally, there has been known a three-dimensional coordinate measuring machine that has a drive unit that displaces the position and attitude of a stylus, and that measures various measurement items such as the dimensions and shape of the measurement element by bringing a contactor at the tip of the stylus into contact (probing) with the measurement surface of various measurement elements (e.g., circular holes, flat surfaces, spheres, etc.) formed on the workpiece (object to be measured).

[0003] In such a three-dimensional coordinate measuring machine, measurements corresponding to the measurement items are performed by bringing the contactor into contact with the surface to be measured while displacing the position and attitude of the stylus along a measurement path (measurement route) set along the surface to be measured of the measurement element, based on a measurement program in which a plurality of measurement items related to the workpiece are defined (see Patent Document 1). For this reason, prior to measuring the workpiece with the three-dimensional coordinate measuring machine, several candidate stylus attitudes are prepared using a CAD (Computer Aided Design) model of the workpiece and stylus, and a collision simulation is performed to determine the optimal stylus attitude.

[0004] Japanese Patent Application Laid-Open No. 2015-222196

[0005] In recent years, additive manufacturing has made it possible to manufacture workpieces with shapes that were previously difficult to manufacture. This has resulted in the need for complex shapes for the measurement features of the workpiece (e.g., curved holes and curved gaps). Therefore, in order to determine the optimal stylus posture on a measurement path set along the measurement surface of a complex-shaped measurement feature using the collision simulation described above, it is necessary to prepare a large number of possible stylus postures (with fine angular resolution), which increases the number of trials. This results in an increased computational cost.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a stylus attitude determination method and a stylus attitude determination device that can reduce the calculation cost required to determine the optimal stylus attitude even when the surface to be measured has a complex shape.

[0007] A stylus orientation determination method for achieving the object of the present invention is a stylus orientation determination method for determining the orientation of a stylus at multiple positions on a measurement path when the tip of the stylus of a coordinate measuring machine is moved along a measurement path that is set in advance along the surface to be measured, the method comprising: a model acquisition step for acquiring a measurement surface model that models the surface to be measured and a stylus model that models the stylus; an initial setting step for setting the tip of the stylus model at a measurement path position that is a position on the measurement path that is set along the measurement surface model; an evaluation point setting step for setting multiple evaluation points along the surface of the stylus model; a normal setting step for setting a normal to the surface of the stylus model for each evaluation point; a shortest distance point setting step for setting a shortest distance point on the measurement surface model that has the shortest distance from each evaluation point; a determination step for determining, when the direction of the normal is the normal direction, whether or not the shortest distance point corresponding to the evaluation point satisfies a condition that the shortest distance point corresponding to the evaluation point is located on the normal direction side of the evaluation point relative to the tangent plane of the stylus model at the evaluation point; a distance vector calculation step that calculates a distance vector between a suitable evaluation point and a shortest distance point for each suitable evaluation point that satisfies the conditions based on the judgment result of the step; a pressure vector calculation step that calculates a pressure vector that is virtually applied to the suitable evaluation point in a direction opposite to the normal direction for each suitable evaluation point based on the calculation result of the distance vector calculation step; a moment calculation step that calculates a virtual moment centered on the measurement path position for each suitable evaluation point based on the calculation result of the pressure vector calculation step; a repetitive control step that repeatedly executes processing from the evaluation point setting step to the moment calculation step at multiple rotational angle positions of the stylus model while rotating the stylus model around a rotation axis set at the measurement path position; and an optimal attitude determination step that determines the optimal attitude of the stylus in a direction around the axis of the rotation axis based on the calculation result of the moment calculation step for each rotational angle position, and repeatedly executes steps from the initial setting step to the optimal attitude determination step for each measurement path position on the measurement path.

[0008] According to this stylus attitude determination method, even if the surface to be measured has a complex shape, the optimum attitude of the stylus can be easily determined for each measurement path position on the measurement path set along the surface to be measured.

[0009] In another aspect of the stylus attitude determination method of the present invention, the moment calculation step calculates the total moment of the moments for each compatible evaluation point, and the optimal attitude determination step determines the optimal attitude based on the total moment calculated in the moment calculation step for each rotation angle position.

[0010] In a stylus attitude determination method according to another aspect of the present invention, the determining step determines whether a condition is satisfied for each evaluation point based on whether the angle between the direction of the distance vector and the normal direction is less than π / 2, thereby making it possible to determine whether the condition that the shortest-distance point is located on the normal direction side of the evaluation point relative to the tangent plane at the evaluation point is satisfied.

[0011] In the stylus attitude determination method according to another aspect of the present invention, the magnitude of the pressure vector calculated in the pressure vector calculation step is inversely proportional to the magnitude of the distance vector.

[0012] In a stylus attitude determining method according to another aspect of the present invention, a storing step is executed in which the optimum attitude determined in the optimum attitude determining step is stored in a storage unit for each measurement path position.

[0013] In a stylus attitude determination method according to another aspect of the present invention, the measurement path is set to be non-linear in accordance with the non-linear measurement surface.

[0014] In a stylus orientation determination method according to another aspect of the present invention, the stylus is non-linear, so that even if the surface to be measured and the measurement path have non-linear shapes, the tip of the stylus can be moved along the measurement path from its start point to its end point.

[0015] A stylus attitude determination device for achieving the object of the present invention determines the attitude of a stylus at a plurality of positions on a measurement path when the tip of the stylus of a coordinate measuring machine is moved along a measurement path that is set in advance along the surface to be measured, and includes a model acquisition unit that acquires a measurement surface model that models the surface to be measured and a stylus model that models the stylus, an initial setting unit that sets the tip of the stylus model at a measurement path position that is a position on the measurement path that is set along the measurement surface model, an evaluation point setting unit that sets a plurality of evaluation points along the surface of the stylus model, a normal line setting step that sets a normal to the surface of the stylus model for each evaluation point, a shortest distance point setting unit that sets, on the measurement surface model for each evaluation point, a shortest distance point that is the shortest distance from the evaluation point, and a step that checks whether, when the direction of the normal line is the normal direction, the shortest distance point corresponding to the evaluation point satisfies a condition that, for each evaluation point, the shortest distance point corresponding to the evaluation point is located on the normal direction side of the evaluation point relative to a tangent plane of the stylus model at the evaluation point a distance vector calculation unit that calculates a distance vector between a suitable evaluation point and a shortest distance point based on the determination result of the determination unit for each suitable evaluation point that satisfies the conditions; a pressure vector calculation unit that calculates a pressure vector that is virtually applied to the suitable evaluation point in a direction opposite to the normal direction based on the calculation result of the distance vector calculation unit for each suitable evaluation point; a moment calculation unit that calculates a virtual moment centered on the measurement path position for each suitable evaluation point based on the calculation result of the pressure vector calculation unit; a repetitive control unit that repeatedly operates from the evaluation point setting unit to the moment calculation unit at multiple rotational angle positions of the stylus model while rotating the stylus model around a rotation axis set at the measurement path position; and an optimal attitude determination unit that determines the optimal attitude of the stylus in a direction around the rotation axis based on the calculation result of the moment calculation unit for each rotational angle position on the measurement path, and repeatedly operates from the initial setting unit to the optimal attitude determination unit for each measurement path position on the measurement path.

[0016] The present invention can reduce the calculation cost required to determine the optimum attitude of the stylus even if the surface to be measured has a complex shape.

[0017] 1 is a schematic diagram of a three-dimensional coordinate measuring machine and a computer; 2 is a diagram showing an example of a stylus shape and a measurement path showing a movement path of the tip (contact) of the stylus when measuring the shape of a curved hole (hole inner surface); 3 is a functional block diagram of the computer; ｎ The measurement path position O is the starting point of ０ 1 is an explanatory diagram for explaining the initial setting by the initial setting unit, the setting of the evaluation point by the evaluation point setting unit, and the setting of the normal line by the normal line setting unit in the measurement path position O ０ 10 is an explanatory diagram for explaining the setting of the shortest distance point by the shortest distance point setting unit, the determination by the determination unit, and the calculation of the distance vector by the distance vector calculation unit in the measurement path position O ０ 10 is an explanatory diagram for explaining calculation of a virtual pressure vector by a pressure vector calculation unit at a measurement path position O ０ 1 is an explanatory diagram for explaining calculation of a virtual moment by a moment calculation unit at a measurement path position O ０ 1 is an explanatory diagram for explaining the repeat control by the repeat control unit in the measurement path position O １ 1 is an explanatory diagram for explaining determination of the optimum posture of the stylus at an arbitrary measurement path position O ｎ 11 is an explanatory diagram for explaining the optimal attitude of the stylus in Fig. 11. Fig. 12 is a flowchart showing the flow of a measurement program generation process by a computer. Fig. 13 is a flowchart showing the flow of an optimal attitude determination process (step S3) in Fig. 11. Fig. 14 is a flowchart showing the flow of an optimal attitude determination process (step S3) in Fig. 11.

[0018] 1 is a schematic diagram of a three-dimensional coordinate measuring machine 10, which corresponds to the coordinate measuring machine of the present invention, and a computer 100, which corresponds to the stylus attitude determining device of the present invention. Note that the mutually orthogonal X, Y and Z axes in Fig. 1 indicate the X, Y and Z directions of a machine coordinate system that is determined based on the machine coordinate origin specific to the three-dimensional coordinate measuring machine 10.

[0019] 1, a three-dimensional coordinate measuring machine 10 uses a coordinate measurement stylus 26 (also referred to as a stylus shaft or a probe) that supports contact measurement to perform shape measurement of one or more measurement elements of a workpiece W, which is an object to be measured. In this embodiment, an example will be described in which the shape of a curved hole 200 (measurement element) formed in the workpiece W is measured.

[0020] The three-dimensional coordinate measuring machine 10 includes a base 12, a table 14 (surface plate) provided on the base 12, a right Y carriage 16R and a left Y carriage 16L provided upright at both ends of the table 14, and an X guide 18 connecting the upper parts of the right Y carriage 16R and the left Y carriage 16L. The right Y carriage 16R, the left Y carriage 16L, and the X guide 18 form a portal frame 19.

[0021] Sliding surfaces along which the right Y carriage 16R and left Y carriage 16L slide in the Y direction are formed on the top and side surfaces of both ends of the table 14 in the X direction. Air bearings (not shown) are provided on the right Y carriage 16R and left Y carriage 16L at positions facing the sliding surfaces of the table 14. This allows the right Y carriage 16R and left Y carriage 16L to move freely in the Y direction together with the X guide 18.

[0022] An X carriage 20 is attached to the X guide 18. A sliding surface along the X direction is formed on this X guide 18, along which the X carriage 20 slides. An air bearing (not shown) is also provided on the X carriage 20 at a position opposite the sliding surface of the X guide 18. This allows the X carriage 20 to move freely in the X direction.

[0023] A Z carriage 22 (also called a Z spindle) is attached to the X carriage 20. The X carriage 20 is also provided with a Z-direction guide air bearing (not shown) that guides the Z carriage 22 in the Z direction. This allows the Z carriage 22 to be held by the X carriage 20 so that it can move in the Z direction. A head 24 that selectively holds various types of styluses 26 is provided at the bottom end of the Z carriage 22.

[0024] The three-dimensional coordinate measuring machine 10 is also provided with an XYZ drive unit (not shown) that moves the portal frame 19 in the Y direction, the X carriage 20 in the X direction, and the Z carriage 22 in the Z direction. The XYZ drive unit is a known actuator constituted by, for example, a motor. Driving this XYZ drive unit makes it possible to move the head 24 (stylus 26) in the X, Y, and Z directions.

[0025] The head 24 is, for example, a five-axis simultaneous control head equipped with a stepless positioning mechanism. The head 24 is provided with a rotation drive unit (not shown) such as a motor that rotates the stylus 26 around a rotation axis parallel to the Z direction and around a rotation axis perpendicular to the Z direction. Driving the rotation drive unit makes it possible to change the orientation of the stylus 26. Note that the head 24 may be a six-axis simultaneous control head that combines rotation around the X, Y, and Z axes and three other axes, or may be one that has six degrees of freedom in the position and orientation of the stylus 26, such as an articulated robot.

[0026] The stylus 26 is detachably attached to the head 24. The stylus 26 is a contact-type touch-trigger stylus, and has a known contactor 26a (probing ball) at its tip. The shape of the stylus 26 will be described later. Instead of using the contact-type stylus 26, a non-contact type may be used. Also, instead of using the touch-trigger type stylus 26, a scanning type may be used.

[0027] The three-dimensional coordinate measuring machine 10 includes a controller 29 that controls the movement of the head 24 , that is, the position and attitude of the stylus 26 , by controlling the XYZ drive unit and the rotation drive unit (not shown) described above.

[0028] When the three-dimensional coordinate measuring machine 10 is in the manual measurement mode, the controller 29 drives an XYZ drive unit and a rotation drive unit (not shown) in response to operation input from the user (operator) to change the position and attitude of the stylus 26. When the three-dimensional coordinate measuring machine 10 is in the automatic measurement mode, the controller 29 drives the XYZ drive unit and the rotation drive unit under the control of the control device 30 to move the stylus 26 along a measurement path 202 (see FIG. 2 ) set along the inner surface 200 a of the curved hole 200 (corresponding to the surface to be measured in this invention) and to change its attitude.

[0029] Connected to the controller 29 are a contact detection sensor (not shown) for the contact touch trigger type stylus 26, a position detection sensor (not shown) that detects the XYZ position coordinates of the head 24, and an attitude detection sensor (not shown) that detects the angle (attitude) of the stylus 26. The controller 29 acquires the detection results of the position detection sensor and the attitude detection sensor and outputs them to the control device 30 the moment the contact detection sensor detects that the stylus 26 has come into contact with the measurement point on the surface to be measured (the inner surface 200 a of the hole).

[0030] The control device 30 is connected to the controller 29 via a known communication interface such as a LAN (Local Area Network) so as to be able to communicate data. The control device 30 comprehensively controls the operations of each part of the three-dimensional coordinate measuring machine 10. The control device 30 controls the movement and attitude of the stylus 26 along a measurement path 202 (see FIG. 2 ) by controlling the controller 29 in accordance with a measurement program 114 input from the computer 100 (described later). The control device 30 also generates shape measurement data of the hole inner surface 200 a, etc., based on detection results, etc., of a position detection sensor and an attitude detection sensor (not shown) input from the controller 29.

[0031] 2 is a diagram showing an example of the shape of the stylus 26 and a measurement path 202 showing the movement path of the tip (contact 26a) of the stylus 26 when measuring the shape of the curved hole 200 (hole inner surface 200a). As shown in Fig. 2, the measurement path 202 is set in a spiral shape so as to follow the hole inner surface 200a from one opening of the curved hole 200 to the other opening.

[0032] The stylus 26 is formed in a curved shape corresponding to the shape of the curved hole 200 so that the contact 26a can be moved from one opening of the curved hole 200 to the other opening along the measurement path 202. In this way, when the measurement element such as the curved hole 200 in the workpiece W has a complex shape (non-linear), the stylus 26 is also formed in a non-linear shape such as a curved shape to correspond to this complex shape.

[0033] 1, the computer 100 generates in advance a measurement program 114 corresponding to the shape measurement of the curved hole 200 in the workpiece W. The measurement program 114 includes at least coordinate data of a measurement path 202 corresponding to the curved hole 200 in the workpiece W, and a position on this measurement path 202 [hereinafter referred to as measurement path position O]. ｎ (n is a natural number of 0 to N, where N is 1 or more) and the optimal posture of the stylus 26 for each of these positions. This measurement program 114 is input to the control device 30. This enables the three-dimensional coordinate measuring machine 10 to automatically measure the shape of the curved hole 200.

[0034] The measurement program 114 may be generated by the control device 30 of the three-dimensional coordinate measuring machine 10. In this case, the control device 30 functions as the stylus attitude determining device of the present invention.

[0035] 3 is a functional block diagram of the computer 100. The computer 100 includes a calculation device 102, a storage unit 104, an operation unit 106, and a display unit 108.

[0036] The calculation device 102 includes a calculation circuit configured with various processors and memories, etc., and calculates the measurement path position O ｎThe computing device 102 determines the optimal posture of the stylus 26 for each measurement and generates the measurement program 114. The various processors include a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), and a programmable logic device (e.g., a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)). The various functions of the computing device 102 may be realized by a single processor, or by multiple processors of the same or different types.

[0037] The memory unit 104 stores a control program (not shown) for the arithmetic device 102, as well as a workpiece model WM (corresponding to the measurement surface model of the present invention), a stylus model 26M, optimal posture information 112, a measurement program 114, and the like.

[0038] The workpiece model WM is a CAD model (also referred to as CAD data) that models the workpiece W (hole inner surface 200a), and is stored in the storage unit 104 for each workpiece W whose shape is to be measured by the three-dimensional coordinate measuring machine 10. The stylus model 26M is a CAD model that models the stylus 26, and is stored in the storage unit 104 for each type of stylus 26. The optimal attitude information 112 is a CAD model that models the measurement path position O determined by the calculation device 102. ｎ The measurement program 114 is information indicating the optimum posture of the stylus 26 for each measurement. The measurement program 114 is generated by the arithmetic unit 102 and is stored.

[0039] The operation unit 106 is configured with, for example, a keyboard, a mouse, etc., and accepts input of various operations by the user. The various operations include, for example, an operation for selecting a CAD model (workpiece model WM and stylus model 26M) corresponding to the workpiece W whose shape is to be measured and the stylus 26 used for shape measurement, an operation for setting the measurement path 202, and an operation for starting determination of the optimal posture, which will be described later.

[0040] Various information is displayed on the display unit 108. For example, when the measurement program 114 is generated, the measurement path position O ｎ A simulation screen 300 (see FIG. 4) for determining the optimum posture of the stylus 26 for each measurement is displayed on the display unit 108. After the measurement program 114 is generated, the measurement program 114 can be displayed on the display unit 108.

[0041] By executing a control program (not shown) stored in the memory unit 104, the calculation device 102 functions as a CAD model acquisition unit 120, a measurement path setting unit 122, an initial setting unit 124, an evaluation point setting unit 126, a normal setting unit 128, a shortest distance point setting unit 130, a judgment unit 132, a distance vector calculation unit 134, a pressure vector calculation unit 136, a moment calculation unit 138, a repetitive control unit 140, an optimal posture determination unit 142, a memory control unit 144, and a measurement program generation unit 146.

[0042] The CAD model acquisition unit 120 corresponds to the model acquisition unit of the present invention, and in response to a CAD model selection operation input to the operation unit 106, acquires the workpiece model WM and stylus model 26M selected in this CAD model selection operation from the storage unit 104. Here, the CAD model selection operation includes a selection operation for selecting the workpiece model WM of the workpiece W whose shape is to be measured, and a selection operation for selecting the stylus model 26M of the stylus 26 used to measure the shape of the workpiece W. Note that instead of acquiring the workpiece model WM and stylus model 26M from the storage unit 104, the CAD model acquisition unit 120 may acquire the workpiece model WM and stylus model 26M from an external server via a known communication network.

[0043] Based on the workpiece model WM and the stylus model 26M acquired by the CAD model acquisition unit 120, the measurement path 202 is set and the measurement path position O ｎ and determining the optimum posture of the stylus 26 for each time period.

[0044] Furthermore, a simulation screen 300 (see FIG. 4 ) is displayed on the display unit 108 based on the workpiece model WM and the stylus model 26M acquired by the CAD model acquisition unit 120. This allows the user to perform operations such as setting the measurement path 202 and starting to determine the optimal posture (described later) based on the simulation screen 300 displayed on the display unit 108.

[0045] The measurement path setting unit 122 sets the measurement path 202 along the hole inner surface 200a of the workpiece model WM in response to an input of a setting operation for the measurement path 202 to the operation unit 106. For example, the measurement path setting unit 122 analyzes the shape of the hole inner surface 200a based on the workpiece model WM, and automatically sets the measurement path 202 based on the analysis results and the measurement items for the hole inner surface 200a. Alternatively, the user may set the measurement path 202 by performing a designation operation to designate the route (start point, multiple relay points, and end point) of the measurement path 202 on the workpiece model WM displayed on the display unit 108. In this case, the measurement path setting unit 122 sets the measurement path 202 along the route designated by the user.

[0046] The method for setting the measurement path 202 is a known technique, and therefore the method for setting the measurement path 202 is not particularly limited to the above-described method.

[0047] The initial setting unit 124 to the optimal attitude determination unit 142 determine the individual measurement path positions O ｎ It acts in determining the optimum posture of the stylus 26 for each scan.

[0048] FIG. 4 shows the measurement path position O ｎ The measurement path position O is the starting point of ０ The initial setting by the initial setting unit 124 and the evaluation point p ｉ and the normal n by the normal setting unit 128 ｉ 10 is an explanatory diagram for explaining the setting of

[0049] 4, the initial setting unit 124 operates in response to an operation to start determining the optimum posture on the operation unit 106. The initial setting unit 124 starts the process of setting the measurement path position O on the simulation screen 300. ０The contact 26a, which is the tip of the stylus model 26M, is set in the stylus model 26M.

[0050] The evaluation point setting unit 126 is activated when the initial setting is completed by the initial setting unit 124. The evaluation point setting unit 126 sets a plurality of evaluation points p along the surface of the stylus model 26M. ｉ (i=1 to K: K is a natural number of 2 or more) are set. In order to prevent the drawing from becoming too complicated, evaluation points P ｉ Although the evaluation score P ｉ The setting position of is not particularly limited as long as it is on the surface of the stylus model 26M (the same applies below).

[0051] In this embodiment, evaluation points p ｉ are set at approximately equal intervals, but the evaluation point p ｉ may be set at uneven intervals.

[0052] The normal setting unit 128 sets the evaluation point p ｉ The normal setting unit 128 operates every time the evaluation point p ｉ For each normal n ｉ For example, the normal setting unit 128 sets the surface shape of the stylus model 26M and each evaluation point p ｉ and the position coordinates of the evaluation point p ｉ The normal setting unit 128 calculates the tangent plane T (see FIG. 5) of the stylus model 26M for each evaluation point p ｉ Based on the calculation result of the tangent plane T for each point, the evaluation point p ｉ Normal n perpendicular to the tangent plane T for each ｉ Hereafter, normal n ｉ The direction is called the "normal direction."

[0053] FIG. 5 shows the measurement path position O ０ The shortest distance point Pc ｉ 13A and 13B are explanatory diagrams for explaining the setting of the distance vector d, the determination by the determination unit 132, and the calculation of the distance vector d by the distance vector calculation unit 134.

[0054] As shown in FIG. 5, the shortest distance point setting unit 130 sets the evaluation point p ｉ Whenever the normal line setting unit 128 sets the normal line n ｉ The shortest distance point setting unit 130 operates every time the evaluation point p set by the evaluation point setting unit 126 on the simulation screen 300 is set. ｉ For each, evaluation score p ｉ Based on the position of the workpiece and the workpiece model WM, this evaluation point p ｉ The shortest distance point Pc is the point where the distance between ｉ is set on the inner surface 200a of the hole of the workpiece model WM (see FIG. 10 described later).

[0055] The determination unit 132 determines whether the shortest distance point Pc ｉ The determination unit 132 operates every time the evaluation point p ｉ For each evaluation point p ｉ The shortest distance point Pc corresponding to ｉ is the evaluation score p ｉ The evaluation point p is located at the tangent plane T of the stylus model 26M. ｉ It is determined whether the condition that the point is located on the normal line side of the point (hereinafter abbreviated as the shortest distance point position condition) is satisfied.

[0056] For example, the determination unit 132 determines whether the shortest distance point Pc ｉ and evaluation score p ｉ Vector Vc between ｉ [Vc ｉ = PC ｉ -p ｉ (equivalent to the distance vector d described later)]. Then, the determination unit 132 calculates the vector Vc ｉ direction and normal direction (normal n ｉ ) and the angle [= cos －１ (Vc ｉ ・n ｉ / (|Vc ｉ | |n ｉ |)))] and determines whether the shortest-distance point position condition is satisfied based on whether this angle is less than π / 2. The determination result of this determination unit 132 is output to distance vector calculation unit 134.

[0057] The distance vector calculation unit 134 calculates the evaluation point p ｉ The evaluation point p satisfies the shortest distance point position condition. ｉ (Hereafter, the conformity evaluation score p ｉ The distance vector calculation unit 134 is activated each time it is determined that the matching evaluation point p ｉ and the shortest distance point Pc ｉ Based on the position coordinates of the matching evaluation point p ｉ For each, the conformance evaluation score p ｉ The shortest distance point Pc ｉ The distance vector d (d = |Pc ｉ -p ｉ |) is calculated.

[0058] FIG. 6 shows the measurement path position O ０ In this case, the virtual pressure vector V ｉ FIG. 10 is an explanatory diagram for explaining the calculation of

[0059] As shown in FIG. 6, the pressure vector calculation unit 136 calculates the matching evaluation point p ｉ The pressure vector calculation unit 136 operates every time it calculates the distance vector d for each matching evaluation point p ｉ For each point, a matching evaluation point p is calculated based on the calculation result of the distance vector d by the distance vector calculation unit 134. ｉ A pressure vector V is virtually applied in the direction opposite to the normal direction to ｉ Calculate the following.

[0060] Specifically, the pressure vector calculation unit 136 calculates the matching evaluation point p ｉ For each, a virtual pressure vector V ｉ V ｉ = -(1 / d)n ｉ In this calculation, the pressure vector V is expressed as (1 / d). ｉ is inversely proportional to the magnitude of the distance vector d. This is because it is assumed that the closer the workpiece model WM (hole inner surface 200a) is to the stylus model 26M, the stronger the pressure applied from the workpiece W to the stylus 26, and that this pressure acts as a force that moves the stylus 26 away from the workpiece W.

[0061] FIG. 7 shows the measurement path position O ０ In this case, the virtual moment M calculated by the moment calculation unit 138 ｉ FIG. 10 is an explanatory diagram for explaining the calculation of

[0062] As shown in FIG. 7, the moment calculation unit 138 calculates the matching evaluation point p ｉ Pressure vector V for each ｉ The moment calculation unit 138 operates every time it calculates the matching evaluation point p ｉ The pressure vector V ｉ Based on the calculation result, the measurement path position O ０ Pressure vector V centered at ｉ The virtual moment M ｉ Specifically, the moment calculation unit 138 calculates the matching evaluation point p ｉ For each, a virtual moment M ｉ M ｉ = (P ｉ -O ０ ) x V ｉ The calculation is performed using the following formula.

[0063] The moment calculation unit 138 also calculates the matching evaluation point p ｉ Moment M ｉ The total moment M (M = Σ [i = 1, ... K] M ｉ ) is calculated.

[0064] FIG. 8 shows the measurement path position O ０ 10 is an explanatory diagram for explaining the repetition control by the repetition control unit 140 in FIG.

[0065] 8, the repetitive control unit 140 operates after the moment calculation unit 138 calculates the total moment M. Based on the calculation result of the total moment M, the repetitive control unit 140 displays the measurement path position O on the simulation screen 300. ０ The stylus model 26M is rotated by an angle r (r=a|M| [rad]) around the rotation axis C set at the measurement path position O. ０is a straight line in the direction of the total moment M passing through. Here, "a" in the above equation is an optimization coefficient, and is a value obtained by experiment or the like. As a result, the attitude of the stylus model 26M rotates by an angle r around the rotation axis C.

[0066] Next, the repetitive control unit 140 executes repetitive control to repeatedly operate each unit from the evaluation point setting unit 126 to the moment calculation unit 138. As a result, the evaluation point setting unit 126 sets a plurality of evaluation points p ｉ and the normal setting unit 128 sets the evaluation point p ｉ Normal for each n ｉ and the evaluation point p ｉ The shortest distance point Pc ｉ and the evaluation score p ｉ and the distance vector calculation unit 134 calculates the matching evaluation point p ｉ The distance vector d is calculated for each point, and the pressure vector calculation unit 136 calculates the matching evaluation point p ｉ Pressure vector V for each ｉ and the matching evaluation point p ｉ Moment M ｉ and the calculation of the total moment M are repeatedly performed.

[0067] Similarly, the repetitive control unit 140 rotates the stylus model 26M by an angle r around the rotation axis C, and executes repetitive control to repeatedly operate each unit from the evaluation point setting unit 126 to the moment calculation unit 138 at a plurality of rotation angle positions of the stylus model 26M. As a result, the total moment M at a plurality of rotation angle positions of the stylus model 26M is calculated. That is, ０ When the attitude of the stylus model 26M is changed in the direction around the axis of the stylus model 26M, the total moment M for each attitude of the stylus model 26M is calculated.

[0068] The optimum attitude determination unit 142 operates when the calculation of the total moment M at all rotation angle positions of the stylus model 26M is completed. The optimum attitude determination unit 142 compares the total moment M for each rotation angle position of the stylus model 26M and determines the measurement path position O. ０ The optimum attitude of the stylus 26 in the direction around the axis of rotation C at

[0069] Specifically, the total moment M becomes smaller as both the first contour line 27a and the second contour line 27b (see FIG. 4) of the stylus model 26M are separated in a balanced manner from the inner surface 200a of the hole in the workpiece W (see FIG. 10 described later). Therefore, the optimal posture determination unit 142 determines the rotational angle position of the stylus model 26M corresponding to the smallest total moment M among the total moments M for each rotational angle position of the stylus model 26M as the measurement path position O. ０ The optimum posture of the stylus 26 is determined as

[0070] The memory control unit 144 stores the measurement path position O determined by the optimal attitude determination unit 142. ０ The optimum attitude of the stylus 26 at this point is stored as optimum attitude information 112 in the storage unit 104.

[0071] FIG. 9 shows the measurement path position O １ 10 is an explanatory diagram for explaining determination of the optimum attitude of the stylus 26 in the embodiment. FIG.

[0072] As shown in FIG. ０ After the optimal posture of the stylus 26 is determined, the initial setting unit 124 moves the contact 26a of the stylus model 26M to the measurement path position O on the simulation screen 300 in response to an optimal posture determination start operation on the operation unit 106. １ At this time, the attitude of the stylus model 26M may be rotated as appropriate.

[0073] Next, the measurement path position O ０ Similarly to the determination of the optimum posture of the stylus 26 in the above, the units from the evaluation point setting unit 126 to the optimum posture determination unit 142 operate to determine the measurement path position O １The optimum attitude of the stylus 26 in the direction around the axis of rotation C at the measurement path position O is determined. １ The optimum attitude of the stylus 26 at this point is stored as optimum attitude information 112 in the storage unit 104.

[0074] FIG. 10 shows an arbitrary measurement path position O ｎ 10 is an explanatory diagram for explaining the optimal posture of the stylus 26 in the case where the evaluation point p ｉ is determined by the determination unit 132 as a matching evaluation score p ｉ Non-conforming evaluation points p that are not judged to be ｉ In addition, the non-conformity evaluation score p ｉ The imaginary pressure vector V applied to ｉ is defined as "0".

[0075] As shown in FIG. 10, the measurement path position O ０ and measurement path position O １ Similarly to determining the optimum orientation of the stylus 26 at ｎ The optimum attitude of the stylus 26 at this point is determined and stored as optimum attitude information 112 in the storage unit 104.

[0076] 3 , the measurement program generation unit 146 generates a measurement program 114 for measuring the shape of the curved hole 200 in the workpiece W by a known method based on the measurement path 202 set by the measurement path setting unit 122 and the optimal posture information 112 in the storage unit 104, and stores the measurement program 114 in the storage unit 104. This measurement program 114 is input to the control device 30 of the three-dimensional coordinate measuring machine 10.

[0077] [Operation of this embodiment] Fig. 11 is a flowchart showing the flow of the process of generating the measurement program 114 by the computer 100. Figs. 12 and 13 are flowcharts showing the flow of the optimal attitude determination process (step S3) in Fig. 11 according to the stylus attitude determination method of the present invention.

[0078] 11, first, the user inputs a CAD model selection operation to the operation unit 106. In response to this CAD model selection operation, the CAD model acquisition unit 120 of the calculation device 102 acquires the CAD models (workpiece model WM and stylus model 26M) selected by the user from the storage unit 104 (step S1, which corresponds to the model acquisition step of the present invention).

[0079] Furthermore, a display control unit (not shown) of the arithmetic device 102 generates a simulation screen 300 based on the workpiece model WM, the stylus model 26M, etc. acquired by the CAD model acquisition unit 120, and displays it on the display unit 108.

[0080] After the display unit 108 displays the simulation screen 300, the user inputs a setting operation for the measurement path 202 to the operation unit 106. In response to this setting operation, the measurement path setting unit 122 automatically sets the measurement path 202 on the workpiece model WM, or sets the measurement path 202 along the route specified by this selection operation (step S2).

[0081] Then, the individual measurement path positions O of the measurement path 202 are ｎ An optimum posture determination process is started to determine the optimum posture of the stylus 26 for each position (step S3).

[0082] 12 and 13, the user first inputs an operation to start determining the optimum posture to the operation unit 106. In response to this setting operation, the initial setting unit 124 sets the contact 26a of the stylus model 26M to the measurement path position O. ０ (Steps S4 and S5, which correspond to the initial setting steps of the present invention).

[0083] After the initial setting, the evaluation point setting unit 126 sets evaluation points p along the surface of the stylus model 26M. ｉ The evaluation point setting unit 126 first starts setting the evaluation point p １ is set on the surface of the stylus model 26M (steps S7 and S8). Step S8 corresponds to the evaluation point setting step of the present invention.

[0084] Evaluation score p １After setting, the normal setting unit 128 sets the evaluation point p １ Normal n in the normal direction １ is set (step S9, which corresponds to the normal setting step of the present invention).

[0085] Next, the shortest distance point setting unit 130 sets the evaluation point p １ Based on the position of the workpiece and the workpiece model WM, this evaluation point p １ The shortest distance point Pc is the point where the distance between １ is set on the hole inner surface 200a of the workpiece model WM (step S10, which corresponds to the shortest distance point setting step of the present invention).

[0086] Shortest distance point Pc １ After setting, the determination unit 132 determines the shortest distance point Pc １ and evaluation score p １ Vector Vc between １ [Vc １ = PC １ -p １ Then, the determination unit 132 calculates the vector Vc ｉ direction and normal direction (normal n １ ) and the angle [= cos －１ (Vc １ ・n １ / (|Vc １ | |n １ |)))] and determines whether this angle is less than π / 2. １ is the evaluation score p １ The evaluation point p is located at the tangent plane T of the stylus model 26M. １ Whether the evaluation point p １ It is determined whether or not satisfies the shortest distance point position condition (step S11, which corresponds to the determination step of the present invention).

[0087] Evaluation score p １ does not satisfy the shortest distance point position condition (NO in step S11), the process proceeds to step S16, which will be described later.

[0088] Conversely, evaluation score p １If the determination unit 132 determines that the shortest distance point position condition is satisfied (YES in step S11), the distance vector calculation unit 134 calculates the evaluation point p １ The matching score p ｉ (Step S12). Then, the distance vector calculation unit 134 selects the matching evaluation point p １ The shortest distance point Pc １ Distance vector d (= |Pc １ -p １ |) is calculated (step S13, which corresponds to the distance vector calculation step of the present invention).

[0089] After calculating the distance vector d, the pressure vector calculation unit 136 calculates the matching evaluation point p １ Normal direction (normal n １ ) A virtual pressure vector V is applied in the opposite direction to １ [=-(1 / d)n １ ] is calculated (step S14, which corresponds to the pressure vector calculation step of the present invention). １ Based on the calculation results of the above, the moment calculation unit 138 calculates a pressure vector V centered on the rotation axis C. １ The virtual moment M １ (Step S15, which corresponds to the moment calculation step of the present invention).

[0090] Similarly, step S17 (i is incremented by 1) and the processes from step S8 to step S15 described above are repeatedly executed (NO in step S16). ｉ Moment M ｉ is calculated (YES in step S16).

[0091] Then, the moment calculation unit 138 calculates the matching evaluation point p ｉ Moment M ｉ The total moment M is calculated (step S18).

[0092] After calculating the total moment M, the repeat control unit 140 calculates the measurement path position O based on the calculation result of the total moment M. ０The stylus model 26M is rotated by an angle r (= a|M| [rad]) around the rotation axis C set in (step S19: YES, step S20). Next, the repetitive control unit 140 executes repetitive control to repeatedly operate each unit from the evaluation point setting unit 126 to the moment calculation unit 138 (corresponding to the repetitive control step of the present invention). As a result, the processing from step S7 to step S18 described above is repeatedly executed.

[0093] Similarly, the repetitive control unit 140 performs the above-described repetitive control (the processing from step S7 to step S18) at multiple rotational angle positions of the stylus model 26M while rotating the stylus model 26M by angle r around the rotation axis C. As a result, the total moment M for each rotational angle position of the stylus model 26M is calculated.

[0094] When the calculation of the total moment M at all rotation angle positions of the stylus model 26M is completed (NO in step S19), the optimum attitude determination unit 142 compares the total moment M for each rotation angle position and determines the measurement path position O. ０ The optimum attitude of the stylus 26 at the target position is determined (step S21, which corresponds to the optimum attitude determining step of the present invention).

[0095] Then, the memory control unit 144 stores the measurement path position O determined by the optimal attitude determination unit 142. ０ The optimum attitude of the stylus 26 at this point is stored in the storage unit 104 as optimum attitude information 112 (step S22, which corresponds to the storage step of the present invention).

[0096] Similarly, the remaining measurement path positions O ｎ Until the determination of the optimum posture of the stylus 26 is completed (NO in step S23), step S24 (n is incremented by 1) and the processes from step S5 to step S22 described above are repeatedly executed. ｎ The optimum attitude of the stylus 26 at this point is stored in the storage unit 104 as optimum attitude information 112 (YES in step S23). This completes the optimum attitude determination process (step S3).

[0097] Returning to Figure 11, the measurement program generation unit 146 generates a measurement program 114 for measuring the shape of the curved hole 200 using a known method based on the measurement path 202 previously set in step S2 and the optimal posture information 112 in the memory unit 104, and stores it in the memory unit 104 (step S25).

[0098] As described above, in this embodiment, even if the surface to be measured has a complex shape, such as the inner surface 200a of the curved hole 200, the measurement path position O can be calculated by the calculation process (simulation) by the computer 100. ｎ As a result, the optimum posture of the stylus 26 for each measurement path position O can be determined almost automatically. ｎ This reduces the computational cost required to determine the optimum posture of the stylus 26 for each measurement.

[0099] [Others] In the above embodiment, the measurement path position O of the measurement path 202 set along the hole inner surface 200 a of the curved hole 200 ｎ The determination of the optimum posture of the stylus 26 for each measurement surface has been described as an example, but the shape of the measurement surface is not particularly limited. ｎ The present invention can also be applied to determining the optimum posture of the stylus 26 for each measurement.

[0100] In the above embodiment, the stylus 26 is formed in a non-linear shape, but the shape of the stylus 26 is not particularly limited.

[0101] 10... Three-dimensional coordinate measuring machine, 12... Stand, 14... Table, 16L... Left Y carriage, 16R... Right Y carriage, 18... X guide, 19... Gate-shaped frame, 20... X carriage, 22... Z carriage, 24... Head, 26... Stylus, 26M... Stylus model, 26a... Contact, 29... Controller, 30... Control device, 100... Computer, 102... Arithmetic unit, 104... Storage unit, 106... Operation unit, 108... Display unit, 112... Optimal posture information, 114... Measurement program, 120... CAD model Vector acquisition unit, 122... measurement path setting unit, 124... initial setting unit, 126... evaluation point setting unit, 128... normal setting unit, 130... shortest distance point setting unit, 132... judgment unit, 134... distance vector calculation unit, 136... pressure vector calculation unit, 138... moment calculation unit, 140... repetition control unit, 142... optimum attitude determination unit, 144... memory control unit, 146... measurement program generation unit, 200... curved hole, 200a... hole inner surface, 202... measurement path, 300... simulation screen, C... rotation axis, M... total moment, M ｉ …Moment, O ｎ ...Measurement path position, Pc ｉ ...Shortest distance point, p ｉ ...Evaluation point (conformance evaluation point, non-conformance evaluation point), T...tangent plane, V ｉ ...pressure vector, W...workpiece, WM...workpiece model, d...distance vector, n ｉ ...normal, r...angle

Claims

1. A stylus orientation determination method for determining the orientation of a stylus at a plurality of positions on a measurement path when the tip of the stylus of a coordinate measuring machine is moved along a predetermined measurement path along the surface to be measured, comprising: a model acquisition step for acquiring a measurement surface model that models the surface to be measured and a stylus model that models the stylus; an initial setting step for setting the tip of the stylus model at a measurement path position that is a position on the measurement path that is set along the measurement surface model; an evaluation point setting step for setting a plurality of evaluation points along the surface of the stylus model; a normal line setting step for setting a normal to the surface of the stylus model for each of the evaluation points; a shortest distance point setting step for setting, on the measurement surface model for each of the evaluation points, a shortest distance point that is the shortest distance from the evaluation point; and a determination step for determining, for each of the evaluation points, whether or not the shortest distance point corresponding to the evaluation point satisfies a condition that, when the direction of the normal line is taken as the normal direction, the shortest distance point corresponding to the evaluation point is located on the normal direction side of the evaluation point relative to the tangent plane of the stylus model at the evaluation point. a distance vector calculation step of calculating a distance vector between each of the suitable evaluation points that satisfy the condition and the shortest distance point based on the determination result of the determination step; a pressure vector calculation step of calculating a pressure vector that is virtually applied to each of the suitable evaluation points in a direction opposite to the normal direction based on the calculation result of the distance vector calculation step; a moment calculation step of calculating a virtual moment centered on the measurement path position for each of the suitable evaluation points based on the calculation result of the pressure vector calculation step; a repetitive control step of repeatedly executing the processes from the evaluation point setting step to the moment calculation step at a plurality of rotation angle positions of the stylus model while rotating the stylus model around a rotation axis set at the measurement path position; and an optimal attitude determination step of determining an optimal attitude of the stylus in a direction around the rotation axis based on the calculation result of the moment calculation step for each of the rotation angle positions,a stylus attitude determining method that repeatedly executes steps from the initial setting step to the optimum attitude determining step for each of a plurality of measurement path positions on the measurement path; 2. A stylus attitude determination method as described in claim 1, wherein in the moment calculation step, a total moment of the moments for each of the compatibility evaluation points is calculated, and in the optimal attitude determination step, the optimal attitude is determined based on the total moment calculated in the moment calculation step for each of the rotation angle positions.

3. A stylus attitude determination method as described in claim 1, wherein the judgment step determines whether or not the condition is met for each evaluation point based on whether or not the angle between the direction of the distance vector and the normal direction is less than π / 2.

4. A stylus attitude determination method according to claim 1, wherein the magnitude of the pressure vector calculated in the pressure vector calculation step is inversely proportional to the magnitude of the distance vector.

5. A stylus attitude determination method according to any one of claims 1 to 4, further comprising a storage step of storing the optimum attitude determined in the optimum attitude determination step in a storage unit for each measurement path position.

6. A stylus attitude determination method according to any one of claims 1 to 4, wherein the measurement path is set to be non-linear in accordance with the non-linear measurement surface.

7. A method for determining stylus pose as claimed in claim 6, wherein said stylus is non-linear.

8. A stylus attitude determination device that determines the attitude of a stylus at a plurality of positions on a measurement path when the tip of the stylus of a coordinate measuring machine is moved along a predetermined measurement path along the surface to be measured, comprising: a model acquisition unit that acquires a measurement surface model that models the surface to be measured and a stylus model that models the stylus; an initial setting unit that sets the tip of the stylus model at a measurement path position that is a position on the measurement path that is set along the measurement surface model; an evaluation point setting unit that sets a plurality of evaluation points along the surface of the stylus model; a normal line setting step that sets a normal to the surface of the stylus model for each of the evaluation points; a shortest distance point setting unit that sets, for each of the evaluation points, a shortest distance point on the measurement surface model that is the shortest distance from the evaluation point; and a determination unit that determines, for each of the evaluation points, whether or not the shortest distance point corresponding to the evaluation point satisfies a condition that, when the direction of the normal line is the normal direction, the shortest distance point corresponding to the evaluation point is located on the normal direction side of the evaluation point relative to the tangent plane of the stylus model at the evaluation point. a pressure vector calculation unit that calculates, for each of the suitable evaluation points, a pressure vector that is virtually applied to the suitable evaluation point in a direction opposite to the normal direction based on the calculation result of the distance vector calculation unit; a moment calculation unit that calculates, for each of the suitable evaluation points, a virtual moment centered on the measurement path position based on the calculation result of the pressure vector calculation unit; a repetitive control unit that repeatedly operates from the evaluation point setting unit to the moment calculation unit at a plurality of rotational angle positions of the stylus model while rotating the stylus model around a rotation axis set at the measurement path position; and an optimal attitude determination unit that determines an optimal attitude of the stylus in a direction around the rotation axis based on the calculation result of the moment calculation unit for each of the rotational angle positions,

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