JP2010234520A - Polishing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a polishing device that always maintains a polishing load at a target value even if the position and posture of a polishing head are simultaneously changed. <P>SOLUTION: An acceleration detecting part 10 mounted to a polishing head 1 detects acceleration in a direction (a Z-direction) that a polishing tool 9 presses a face 17 to be polished. The acceleration to be detected is a sum of gravitational acceleration and a Z-direction component of acceleration by the movement of the polishing head 1. Effects on a polishing load due to changes in position and posture of the polishing head 1 are calculated on the basis of a detected value of the acceleration detecting part 10 so as to control a load that presses the polishing tool 9, thereby maintaining the polishing load at a target value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polishing apparatus that polishes a workpiece such as a lens or a mirror with high accuracy.

  In recent years, higher accuracy is required for optical elements such as lenses and mirrors. In order to realize more accurate polishing, it is necessary to control the polishing removal amount with high accuracy. In general, it is empirically known that the polishing removal amount is proportional to the contact pressure between the polishing tool and the surface to be polished, the relative speed between the polishing tool and the workpiece, and the processing time. Therefore, in order to control the polishing removal amount with high accuracy, it is necessary to control the contact pressure (polishing load) between the polishing tool and the surface to be polished with high accuracy. Therefore, as disclosed in Patent Document 1, the position and posture of the polishing head are controlled so that the polishing load acts in the normal direction of the processing surface, and the predetermined scanning speed distribution and design shape data are determined for the polishing tool. There is a polishing apparatus that performs polishing while scanning according to the above. However, depending on the shape of the workpiece, the posture of the polishing head must be changed in order to make the polishing load coincide with the normal direction of the surface to be polished.

  The change in the posture of the polishing head causes a fluctuation in the polishing load, and causes a problem of inclination that a stable removal amount cannot be obtained. For such a problem, a polishing apparatus (see Patent Document 2) is known that detects the tilt angle of the polishing head and corrects the polishing load based on the detected angle.

  Further, the acceleration when the polishing head moves causes an inertial force in the polishing head, a part of which acts on the polishing load and causes the polishing load to fluctuate. For such a problem, a polishing apparatus (see Patent Document 3) that calculates acceleration from a detection result of a position detector included in the tool drive unit, calculates inertial force based on the acceleration, and corrects polishing load. Are known.

Japanese Patent No. 3304994 JP-A-8-141899 Japanese Patent Laid-Open No. 10-264221

  However, in the polishing head in the polishing apparatus, the tilt problem and the inertia force problem occur at the same time, which may cause the polishing load to vary. Therefore, it is difficult to cope with the conventional technique.

  An object of the present invention is to provide a polishing apparatus capable of obtaining a stable polishing load even when the polishing head moves while accompanying a change in posture.

  The polishing apparatus of the present invention is a polishing apparatus for polishing a workpiece while changing the position and posture of the polishing tool, the polishing tool, and load generating means for generating a load for pressing the polishing tool against the workpiece, Means for changing the relative position and orientation of the polishing tool and the workpiece; acceleration detection means for detecting an acceleration component of the polishing tool in a direction of pressing the polishing tool against the workpiece; and the acceleration detection means Control means for controlling the magnitude of the load generated by the load generating means based on the detected value.

  According to the above configuration, by controlling the load generating means based on the acceleration component in the load direction of the polishing tool, the polishing tool changes its posture and tilts, moves while performing acceleration / deceleration, and tilts and accelerates / decelerates. Even if these are performed simultaneously, the polishing load can always be kept at the target value. That is, the influence on the polishing load due to the inclination and the inertial force can be eliminated at the same time.

  Since only one sensor is required to correct the load variation due to the change in position and orientation, the manufacturing cost of the polishing head can be reduced. In addition, the calculation necessary for correcting the load fluctuation is simplified, and a complicated calculator is not required.

It is a mimetic diagram showing a polish device by one embodiment. It is a schematic cross section which shows the structure of the grinding | polishing head of the apparatus of FIG. It is a schematic cross section which shows the structure of the polishing head by one modification. It is a schematic diagram which shows the structure of the polishing head which has arrange | positioned two acceleration sensors.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows a polishing apparatus according to an embodiment. The polishing apparatus includes a polishing head 1, a link mechanism 2, a load control unit 3, a tool drive control unit 4, and a main control device 5. .

  As shown in FIG. 2, the polishing head 1 includes a load generation unit 6, a load detection unit 7, a tool driving unit 8, a polishing tool 9, an acceleration detection unit (acceleration detection means) 10, and a housing 11. The guide 12, the movable body 13, and the piston 14 are included.

  The tool drive unit 8 performs polishing by rotating the polishing tool 9 in accordance with an instruction from the tool drive control unit 4.

  In the present embodiment, the rotation axis of the polishing tool 9 is installed parallel to the X axis, but the direction of the polishing tool rotation axis is not limited to this. For example, as shown in FIG. 3, a configuration using a polishing tool 29 in which the tool rotation axis is arranged in parallel to the Z axis may be used.

  In this embodiment, the polishing tool 9 is rotated, but the movement of the polishing tool 9 is not limited to rotation. As the movement of the polishing tool 9, rocking and fixing, a combination of rotation and rocking, and the like can be applied. The tool driving unit 8 is fixed to a movable body 13 that moves along a guide 12 fixed to the housing 11. The movable body 13 that moves together with the tool driving unit 8 and the polishing tool 9, the acceleration detection unit 10, and the like are collectively referred to as a “movable unit”.

  The movable body 13 is configured to be movable in the Z direction (the direction in which the polishing tool 9 is pressed against the workpiece 16 on the table 15) along the guide 12 installed inside the housing 11 of the polishing head 1. ing. Therefore, the movable part is not fixed to the housing 11 and can move in the Z direction.

  The load generating unit 6 is a load generating unit that generates a force (load) for moving the movable unit including the movable body 13, the tool driving unit 8, the polishing tool 9, and the acceleration detecting unit 10 in the Z direction. In the present embodiment, an air cylinder is employed as the load generating unit 6, and a piston 14 that can expand and contract according to an instruction from the load control unit 3 is provided. The movable portion is connected to the piston 14 via the load detection portion 7.

  The polishing head 1 polishes the surface to be polished 17 while moving along the surface of the workpiece 16. By expanding and contracting the piston 14, the magnitude of the load for pressing the polishing tool 9 against the surface 17 to be polished can be adjusted.

  The specific configuration of the load generating unit 6 is not limited to the air cylinder. For example, any load controllable device such as a voice coil motor or a combination mechanism of a ball screw and a motor may be used.

  The load detection unit 7 is disposed between the piston 14 and the movable unit, and detects a force acting between the load generation unit 6 and the movable unit. In the present embodiment, a load detection unit 7 is provided for feedback control of a load generated by the load generation unit 6. When the load generated by the load generation unit 6 is controlled by an open loop, the load detection unit 7 is not necessary.

  The acceleration detection unit 10 outputs the sum of the Z-direction acceleration of the center of gravity of the movable portion of the polishing head 1 due to the movement of the polishing head 1 and the Z-direction component of gravitational acceleration as a detection value. That is, the acceleration detection unit as the acceleration detection unit detects an acceleration component in a direction in which the polishing tool is pressed against the workpiece. The acceleration detection unit 10 is capable of detecting static acceleration including gravitational acceleration. In the present embodiment, the acceleration detection unit 10 is configured using an acceleration sensor.

  The link mechanism 2 is a means for supporting the weight of the polishing head 1 and changing the position and posture of the polishing head 1. The link mechanism 2 arbitrarily changes the position and posture at which the polishing tool 9 is pressed against the polishing surface 17 of the workpiece 16 by changing the relative position and posture relative to the table 15 in conjunction with each other. In the present embodiment, a three-axis parallel link mechanism is employed as the link mechanism 2, and the link mechanism 2 can change the position and inclination angle of the polishing head 1 in the Z direction. The specific configuration of the link mechanism 2 is not limited to the parallel link mechanism. The function of changing the position and inclination angle of the polishing head 1 in the Z direction can be realized by a combination of serial link mechanisms. The movement of the polishing head 2 by the link mechanism 2 is not limited to the position and inclination in the Z direction. For example, the link mechanism 2 changes only the position in the Z direction, and the table 15 tilts the workpiece 16 so that the position and posture at which the polishing tool 9 is pressed against the surface 17 to be polished of the workpiece 16 are arbitrary. It is possible to change.

  The table 15 is driven via driving means (not shown) so as to displace the polishing position of the surface 17 to be polished of the workpiece 16. In the present embodiment, the table 15 moves in the X and Y directions and operates in conjunction with the link mechanism 2, so that the relative position and posture of the surface 17 to be polished of the workpiece 16 and the polishing tool 9 are set. Change arbitrarily. The driving direction of the table 15 is not limited to the XY direction. Any driving direction that can arbitrarily change the relative position and posture of the surface 17 to be polished of the workpiece 16 and the polishing tool 9 by interlocking with the operation of the link mechanism 2 may be used.

  The main controller 5 is for controlling and controlling the entire polishing apparatus of the present embodiment in accordance with the input instruction. Note that the main control device 5, the load control unit 3, and the tool drive control unit 4 can actually be configured integrally.

  The load control unit 3 includes a control unit that controls the load generation unit 6 so that the contact pressure between the surface to be polished 17 and the polishing tool 9 maintains an instructed value during polishing. The load control unit 3 performs sequential control based on the detection value of the acceleration detection unit 10, the load detected by the load detection unit 7, and the target value of the polishing load input to the main control device 5. .

  In the present embodiment, the load detection unit 7 is required for feedback control of the load generation unit 6, but the load detection unit 7 is not necessary when the load generation unit 6 is controlled in an open loop.

  The tool drive control unit 4 operates the tool drive unit 8 in accordance with an instruction from the main control device 5.

  In the polishing apparatus configured as described above, correction of a load (polishing load) that presses the polishing tool 9 against the surface to be polished 17 that changes as the position and posture of the polishing head 1 change will be described below.

  When polishing the workpiece 16 having the surface 17 to be polished which is a non-axis target free-form surface, the workpiece 16 is mounted on a table 15 and the polishing tool 9 of the polishing head 1 is mounted as shown in FIG. Then, the workpiece 16 is brought into contact with the workpiece 16 with a predetermined polishing pressure by the load generator 6. Then, the polishing operation is performed while the relative position and posture between the polishing surface 17 of the workpiece 16 and the polishing tool 9 are changed by the interlocking operation of the link mechanism 2 and the table 15. During this polishing process, the link mechanism 2 and the table 15 are operated so that the normal direction of the surface 17 to be polished of the workpiece 16 and the Z direction of the polishing head 1 coincide.

The contact pressure between the polishing tool 9 and the surface to be polished 17 acts on the force generated by the load generating unit 6 and the movable unit (the movable body 13, the tool driving unit 8, the polishing tool 9, and the acceleration detecting unit 10). Determined by gravity and inertial forces. However, not all gravity and inertial force acting on the movable part are added to the contact pressure, but only the Z direction component is included in the contact pressure. That is, the polishing load due to the contact pressure is expressed by the following formula (1).
f = F + M · g _z + M · a _z (1)
here,
f: Polishing load applied to the workpiece 16 (integration of contact pressure between the polishing tool 9 and the polishing surface 17)
F: The magnitude of the load generated by the load generating unit 6 M: Mass of the movable part g _z : Z-direction component of gravity acceleration a _z : Z-direction component of acceleration of the center of gravity of the movable part The formula is obtained.
f = F + M (g _z + a _z ) (2)
(G _z + a _z ) included in the right side of Expression (2) is equal to the detection value of the acceleration detection unit 10 that changes due to the movement of the polishing head 1 and the change in posture. In the present invention, hereinafter, the sum (g _z + a _z ) of the acceleration in the Z direction of the center of gravity of the movable part and the Z direction component of the gravitational acceleration is referred to as the acceleration G of the center of gravity of the movable part. Therefore, when F is constant, the polishing load f varies depending on the movement of the polishing head 1 and the change in posture. In order to keep the polishing load f at a desired value (target value), it is possible to cancel the load fluctuation caused by the movement of the polishing head 1 and the change of the posture by changing the force generated by the load generator 6. is necessary. That is, in order for the polishing load f to be the target value f ₀ , the force generated by the load generator 6 must be {f ₀ −MG}.

Therefore, the load control unit 3 compares {f ₀ -MG} calculated from the output of the acceleration detection unit 10 with the output of the load detection unit 7, and the output of the load detection unit 7 is {f ₀ -M (g _The load generation unit 6 is controlled so as to be _z + a _z )}.

  Thus, even when the position and posture of the polishing head change, the contact pressure between the polishing surface processing surface 17 and the polishing tool 9 can be maintained at a desired value, and stable polishing processing can be performed.

  In the present embodiment, the case where the contact pressure between the surface to be polished 17 and the polishing tool 9 is kept constant has been described. However, by making it possible to set the contact pressure for each position of the surface to be polished, the contact pressure can be set to a different value for each position. Even when the contact pressure is set for each position of the surface to be polished, by applying the present invention, it is possible to always match the polishing load (contact pressure) with the set value.

  The acceleration detector 10 may be arranged at any position as long as it can detect the sum of the Z-direction acceleration of the center of gravity of the movable part and the Z-direction component of the gravitational acceleration, that is, the acceleration G of the center of gravity of the movable part.

  In the embodiment shown in FIG. 2, an example in which the acceleration detection unit 10 is arranged at the center of gravity of the movable unit is shown. In this way, if the acceleration detection unit 10 can be arranged at the center of gravity of the movable unit, the acceleration G of the center of gravity of the movable unit is detected by the acceleration detection unit 10. However, depending on the configuration of the movable part, the acceleration detection part may not be arranged at the center of gravity. When the acceleration detection unit cannot be arranged at the center of gravity of the movable unit, a plurality of acceleration sensors are arranged on the polishing head, and the acceleration G of the center of gravity of the movable unit is calculated from the output result of each acceleration sensor, thereby FIG. The same effect as the embodiment shown can be obtained.

  The relationship between the output of the acceleration sensor arranged on the polishing head and the acceleration G of the center of gravity of the movable part will be described below, and the acceleration G of the center of gravity of the movable part can be obtained by arranging a plurality of acceleration sensors on the polishing head. Indicates that calculation is possible.

  Considering the polishing head as one rigid body, the movement of the polishing head can be thought of as translation and rotation of a head coordinate system fixed to the polishing head relative to the global coordinate system. Consider a head coordinate system in which the center of gravity of the movable part is the reference position (0, 0, 0) and the Z direction of the polishing head is the Z-axis direction. In general, for the movement of the coordinate system, an expression method using a matrix of 4 rows and 4 columns in combination of translation and rotation is used. When the speed and acceleration of the head coordinate system in the global coordinate system are expressed using a matrix, the speed is expressed as Expression (3) and the acceleration is expressed as Expression (4).

Expression (3) indicates that the velocity vector of the head coordinate system is (v _x , v _y , v _z ) and the angular velocity vector is (ω _x , ω _y , ω _z ). Expression (4) indicates that the acceleration vector of the head coordinate system is (b _x , b _y , b _z ) and the angular acceleration vector is (α _x , α _y , α _z ). At this time, the velocity (x ′, y ′, z ′) and acceleration (x ″, y ″, z ″) in the global coordinate system of an arbitrary point (x, y, z) in the head coordinate system are They are represented by formulas (5) and (6), respectively.

  Substituting Equations (3) and (4) into Equation (6) yields Equation (7).

From equation (7), the acceleration of an arbitrary point in the head coordinate system that moves on the global coordinate system can be obtained. Since the position of the center of gravity of the movable part is (0, 0, 0), the acceleration _az at the center of gravity of the movable part due to the movement of the polishing head is as shown in Expression (8).

Since the acceleration G of the center of gravity of the movable part is a _z + g _z , z ″ can be expressed as in Expression (9).

  By transforming equation (9), equation (10) is obtained.

The output of the acceleration sensor arranged at the point (x, y, z) on the polishing head is obtained by adding g _z to the acceleration z ″ of the point (x, y, z) on the polishing head. That is, Formula (10) shows the relationship between the output of the acceleration sensor arranged on the polishing head and the acceleration G of the center of gravity of the movable part.

If (−ω _y ² −ω _x ² ), (ω _y ω _z + α _x ), (ω _x ω _z −α _y ), and G in Equation (10) are regarded as four unknowns, an acceleration sensor is attached to the polishing head. If arranged at four different places, the acceleration G of the center of gravity of the movable part can be calculated.

  Further, when the two points are in the relationship of Expression (11), the acceleration G at the center of gravity of the movable part can be calculated by arranging the acceleration sensors at two locations. When the two points are in the relationship of Expression (11), that is, they are on a straight line passing through (0, 0, 0), that is, on a straight line including the center of gravity of the movable part.

ただしｋは０でない実数

Where k is a non-zero real number

  FIG. 4 shows an example of an embodiment in which the acceleration G at the center of gravity of the movable part can be calculated by arranging the acceleration sensors at two locations. The same parts as those in FIG. In FIG. 4, 18 indicates the center of gravity of the movable part, and 19 and 20 indicate acceleration sensors. Thus, if the acceleration sensors are arranged at two different locations on the straight line including the center of gravity 18 of the movable part, the acceleration G of the center of gravity of the movable part can be calculated.

The Example which has arrange | positioned the acceleration sensor in four places is shown. The coordinates of the center of gravity of the movable part are (0, 0, 0), and the acceleration sensor has coordinates (-100, 100, 100), (-100, -100, 200), (100, -100, 100), respectively. , (100, 100, 200). The acceleration (z ″ + g _z ) detected by the acceleration sensor was set as Ac ₁ , Ac ₂ , Ac ₃ , and Ac ₄ respectively, and the following four formulas were obtained from formula (10).

In Equations (11) to (14), (−ω _y ² −ω _x ² ), (ω _y ω _z + α _x ), (ω _x ω _z −α _y ), G are regarded as four unknowns, The acceleration G of the center of gravity of the movable part was obtained by the following equation (16).

The Example which has arrange | positioned the acceleration sensor in two places is shown. The positions of the acceleration sensors 19 and 20 were (x ₁ , y ₁ , z ₁ ) and k (x ₁ , y ₁ , z ₁ ), respectively. When the acceleration (z ″ + g _z ) detected by the acceleration sensor is set to Ac ₁ and Ac ₂ , the following two expressions are obtained from Expression (10).

From the equations (17) and (18), the acceleration G of the center of gravity of the movable part was obtained by the following equation (19).

DESCRIPTION OF SYMBOLS 1 Polishing head 2 Link mechanism 3 Load control part 4 Tool drive control part 5 Main controller 6 Load generation part 7 Load detection part 8 Tool drive part 9 Polishing tool 10 Acceleration detection part

Claims (5)

In a polishing apparatus for polishing a workpiece while changing the position and posture of a polishing tool,
The polishing tool;
A movable part that moves with the polishing tool in a direction in which the polishing tool is pressed against the workpiece;
Load generating means for generating a load for moving the movable part and pressing the polishing tool against the workpiece;
Means for changing a relative position and posture of the polishing tool and the workpiece;
Acceleration detecting means for detecting the acceleration of the center of gravity of the movable part;
A polishing apparatus comprising: control means for controlling the magnitude of the load generated by the load generating means based on the detected acceleration of the center of gravity of the movable part. 2. The polishing according to claim 1, wherein the control means controls the magnitude F of the load generated by the load generating means based on the detected acceleration of the center of gravity of the movable part as follows. apparatus.
F = f ₀ -MG
f ₀ : Target value of the polishing load by the polishing tool M: Mass of the movable part moving with the polishing tool G: Acceleration of the detected center of gravity of the movable part   The acceleration detecting means is an acceleration sensor arranged at the center of gravity of the movable part, and the detected acceleration of the center of gravity of the movable part is a value detected by an acceleration sensor arranged at the center of gravity of the movable part. The polishing apparatus according to claim 1, wherein the polishing apparatus is provided.   The acceleration detecting means is composed of acceleration sensors arranged at two places on a straight line including the center of gravity of the movable part, and the value of the center of gravity of the movable part is detected from the values detected by the acceleration sensors arranged at the two places. The polishing apparatus according to claim 1, wherein acceleration is calculated.   The acceleration detection means includes acceleration sensors arranged at four locations, and calculates the acceleration of the center of gravity of the movable part from values detected by the acceleration sensors arranged at the four locations. Item 2. The polishing apparatus according to Item 1.

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