JP2011079079A - Polishing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure the polishing load of a rotating polishing tool when pushed against a polished surface, and to control it with high accuracy. <P>SOLUTION: A polishing head includes a casing 9, a tool shaft 1 supported movably in the thrusting direction by a fluid bearing 2, a rotation driving means 7 for driving the tool shaft 1 to rotate, a displacing mechanism 8 for giving a load to the tool shaft 1, and a differential transformer 3 supported by the casing 9. The differential transformer 3 is opposed to a core 4 fixed to the tool shaft 1 and arranged on the lower side of an extensible connection part including a leaf spring 5 connecting the rotation driving means 7 to the tool shaft 1 for measuring the push-in length of the leaf spring 5 to detect the polishing load of a polishing pad 10 on the polished surface 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polishing apparatus for polishing a workpiece.

  In recent years, optical elements such as lenses and mirrors have been required to have higher processing accuracy. In these polishing processes, the polishing head controls the polishing load and the number of rotations of the polishing tool. Generally, it is known as Preston's rule of thumb that the removal amount of polishing is proportional to the contact pressure between the polishing tool and the surface to be polished, the number of revolutions of the polishing tool, and the processing time. Therefore, in order to control the polishing removal amount, the polishing load for pressing the polishing tool against the surface to be polished and the rotation speed of the polishing tool must be controlled. In order to precisely control the polishing load, it is effective to monitor the polishing load and feed back the measured value. In general, a load cell is used to measure the load.

  A conventional polishing head includes a load detection unit such as a load cell and a tool driving unit supported so as to be movable in the load detection direction (see Patent Document 1). As shown in FIG. 6, the polishing head is provided with a load generation unit 108, a load detection unit 103, a rotation driving means 107, and a polishing tool 110. The casing 109 supports the load generation unit 108, and the rotation driving means 107 that rotates the polishing tool 110 can move in the thrust direction of the tool shaft 101 along the guide 106 installed inside the casing 109. It is configured. The load generator 108 moves the rotation driving means 107 to press the polishing tool 110 against the surface to be polished. The polishing load, which is the contact pressure between the polishing tool 110 and the surface to be polished, is added to the load value obtained by the load detection unit 103 due to the weight of the movable part between the load detection unit 103 and the surface to be polished. Can be obtained. Here, the movable portion is configured to be movable in the thrust direction of the tool shaft 101 and refers to a combination of components of the polishing head pressed against the surface to be polished below the load detection unit 103. That is, a combination of the rotation driving means 107, the polishing tool 110, and the tool shaft 101 is a movable part.

  FIG. 7 shows a polishing head according to another example. In this configuration, the load generation unit 108 is supported by the casing 109 via the load detection unit 103, and the combination of the load generation unit 108, the rotation driving unit 107, the polishing tool 110, and the tool shaft 101 is a movable unit. It is.

In any case, when the polishing head is inclined by an angle θ with respect to the direction of gravity, a force (load) ΔF having a magnitude represented by the following equation (1) is polished by the weight of the movable part. It affects the polishing load, which is the contact pressure between the tool 110 and the surface to be polished.
ΔF = M · g · cos θ (1)
Here, ΔF: Load due to weight of movable part among polishing load
M: Mass of the moving part
g: Gravity acceleration
θ: Angle of inclination of the polishing head with respect to the direction of gravity

  The polishing head controls the load generation unit 108 based on a value obtained by adding ΔF to the load value obtained by the load detection unit 103, and an arbitrary polishing load between the polishing tool 110 and the surface to be polished. Can be generated.

Japanese Patent Laid-Open No. 08-141899

However, when the inclination θ with respect to the gravitational direction of the polishing head is not accurately detected, the load value between the polishing tool 110 detected by the polishing head and the surface to be polished has an error E represented by the following equation (2). Including.
E = M · g · (cos (θ + Δθ) −cos θ) (2)
Where E: error included in the load value detected by the polishing head
M: Mass of the moving part
g: Gravity acceleration
θ: Angle of inclination of the polishing head with respect to the direction of gravity
Δθ: Error in tilt angle with respect to gravitational direction of polishing head

  Thus, the error E is proportional to the mass M of the movable part of the polishing head. Among conventional polishing heads, a polishing head that rotates while pressing a polishing tool increases the error of the polishing load detected during the polishing process because the mass of the movable part includes the mass of the rotation driving means. There was a problem.

  An object of this invention is to provide the grinding | polishing apparatus which can control the grinding | polishing load which presses a grinding | polishing tool on a to-be-polished surface with high precision.

  The polishing apparatus of the present invention is a polishing apparatus that polishes a surface to be polished with a rotating polishing tool, the polishing tool, a tool axis that holds the polishing tool and is movable in a thrust direction, and the tool axis. A rotational driving means for rotationally driving, a load applying means for applying a load in the thrust direction to the polishing tool via the tool shaft, and the rotational driving means and the tool shaft are connected to be extendable in the thrust direction. Then, from the expansion / contraction connecting portion for transmitting the rotational torque of the rotation driving means to the tool shaft, the expansion / contraction measuring means for measuring the expansion / contraction length of the expansion / contraction connecting portion, and the expansion / contraction length of the expansion / contraction connecting portion, It has a calculating means for calculating a polishing load when polishing the polishing surface, and a control means for controlling the load applying means in accordance with the output of the calculating means.

  The polishing load, which is a thrust force acting on the tool shaft, can be measured as the expansion / contraction length of the expansion / contraction connecting portion without obstructing the rotation during rotation of the polishing tool. In addition, since the rotational drive means is not included in the movable part below the load measuring part composed of the expansion / contraction connecting part and the expansion / contraction measuring means, the polishing load acting on the surface to be polished is measured with high precision and stable precision. Can be polished.

It is a schematic diagram explaining the structure of the grinding | polishing apparatus by 1st Embodiment. It is a figure which shows the magnet coupling which comprises an expansion-contraction connection part, the gear using a magnet, and the elastic body which can expand-contract elastically and can transmit torque. It is a figure explaining the measuring method of the expansion-contraction length of an expansion-contraction connection part. It is a schematic diagram explaining the structure of the grinding | polishing apparatus by 2nd Embodiment. It is a schematic diagram explaining the structure of the grinding | polishing apparatus by 3rd Embodiment. It is a schematic diagram explaining the structure of the grinding | polishing apparatus by one prior art example. It is a schematic diagram explaining the structure of the grinding | polishing apparatus by another prior art example.

  FIG. 1 shows a polishing apparatus according to a first embodiment. A tool shaft 1 holds a polishing pad 10 as a polishing tool at a lower end and is supported by a fluid bearing 2 so as to be rotatable and movable in a thrust direction. The differential transformer 3 detects the movement of the tool shaft 1 in the thrust direction. The support means for the tool shaft 1 is not necessarily limited to the fluid bearing 2, and a contact-type ball bush or the like may be used. However, a non-contact method such as an air bearing is preferable. The expansion / contraction connecting portion composed of the leaf spring 5 and the leaf spring support 6 connects the rotation driving means 7 and the tool shaft 1 in a telescopic manner, and transmits the rotational torque of the rotation driving means 7 to the tool shaft 1.

  The telescopic connecting portion is not limited to the coupling composed of the leaf spring 5 and the leaf spring support 6. For example, a magnet coupling in which the magnet 61a provided on the cylindrical inner ring 60 shown in FIG. 2A is opposed to the magnet 61b of the outer ring 62, or a pair of gears 63 using the magnet 63a shown in FIG. . Moreover, the structure which can transmit torque and elastically expands-contracts in a thrust direction, such as elastic bodies, such as a metal and resin shown in FIG.2 (c), may be interposed.

  The differential transformer 3 constituting the expansion / contraction measuring means measures the expansion / contraction length of the expansion / contraction connecting portion as a movement amount in the thrust direction of the tool shaft 1 in a non-contact manner by displacement of the core 4 fixed to the tool shaft 1. The expansion / contraction measuring means for measuring the expansion / contraction length of the expansion / contraction connecting portion is not limited to the method using the differential transformer 3. For example, as shown in FIG. 3A, a measurement point 66 on the lower surface of the leaf spring may be measured by a laser displacement meter 65, or as shown in FIG. The measurement point 66 may be arranged on the lower surface. Further, instead of the laser displacement meter, other displacement sensors such as an eddy current displacement meter may be used. A casing 9 is connected to a displacement mechanism 8 which is a load applying means for applying a load in the thrust direction to the polishing pad 10 via the tool shaft 1, and the casing 9 includes a rotation driving means 7, a differential transformer 3, a fluid bearing. 2 is supported. The tool shaft 1 is moved in the thrust direction by the displacement mechanism 8 through the housing 9.

  Next, measurement of the polishing load acting between the polishing pad 10 and the surface 11 to be polished will be described. When the housing 9 is brought close to the workpiece by the displacement mechanism 8, the polishing pad 10 attached to the tip of the tool shaft 1 contacts the surface 11 to be polished while rotating. Even after the polishing pad 10 at the tip of the tool shaft 1 comes into contact with the surface 11 to be polished, the tool shaft 1 is pushed into the leaf spring 5 to deform the leaf spring 5 when the casing 9 is brought close to the workpiece. The indentation length of the tool shaft 1 into the leaf spring 5 (the expansion / contraction length of the expansion / contraction connecting portion) is measured by the differential transformer 3 as the displacement of the core 4. The thrust force (the load in the thrust direction) that the displacement mechanism 8 acts on the tool shaft 1 via the leaf spring 5 can be calculated from the measured value of the pushing length of the leaf spring 5 and existing data by the calculation means 12. . Further, if the mass of the movable part consisting of the polishing pad 10, the tool shaft 1 and the core 4 is measured in advance, the polishing pad 10 and the surface 11 to be polished being polished together with the thrust force acting on the tool shaft 1 will be described. The polishing load acting between the two can be known.

When the polishing head is tilted, the tilt measuring means (not shown) detects the tilt angle of the polishing head with respect to the gravitational direction, corrects the load due to the weight of the movable part by the tilt angle, and the polishing pad 10 and the surface 11 to be polished What is necessary is just to calculate the polishing load acting in between. The polishing load FP is calculated by the following equation (3).
FP = FC + M · g · (1−cos θ) (3)
Here, FP: polishing load acting between the polishing pad 10 and the surface 11 to be polished
FC: Force by which the leaf spring 5 pushes the tool shaft 1
M: Mass of the movable part (total of the masses of the tool shaft 1, the polishing pad 10, and the core 4)
g: Gravity acceleration
θ: Inclination angle of polishing head

  If there is an error in the measurement of the inclination angle θ, the measurement error of the polishing load FP increases in proportion to the mass M of the movable part. Therefore, it is possible to measure the polishing load FP more accurately by reducing the mass M of the movable part.

  In the conventional polishing head, the movable part includes the rotational driving means. However, since the rotational driving means 7 of the polishing apparatus according to the present embodiment is not included in the movable part related to the measurement of the polishing load, the movable part can be reduced in weight. The polishing load can be measured with higher accuracy.

  In the polishing apparatus of this embodiment, in order to increase the polishing load, the displacement mechanism 8 moves the casing 9 so as to approach the surface 11 to be polished, and to decrease the polishing load, the displacement mechanism 8 moves the casing 9 to the polishing apparatus 9. What is necessary is just to move it away from the to-be-polished surface 11.

  In accordance with the output of the calculation means 12 based on the measurement result of the polishing load, the change of the polishing load is reduced by the control means 13 and the displacement mechanism 8 is controlled so as to achieve the target polishing load. The result can be obtained.

  FIG. 4 shows a second embodiment. In the present embodiment, the displacement mechanism 8 is disposed inside the housing 9. As a result, the number of components to be moved by the displacement mechanism 8 is reduced, and the portion to be moved by the displacement mechanism 8 can be reduced in weight, thereby improving the control responsiveness. Further, instead of fixing the differential transformer 3 inside the housing 9 and moving the housing 9 by the displacement mechanism 8, the differential transformer 3 is attached to the differential transformer holder 14 fixed to the displacement mechanism 8 inside the housing. And the rotational drive means 7 is moved by the displacement mechanism 8. The method for measuring the polishing load acting between the polishing pad 10 and the surface 11 to be polished and the polishing process are the same as those in the first embodiment.

  FIG. 5 shows a third embodiment, which measures the indentation length of the tool shaft 1 into the leaf spring 5 with higher accuracy, thereby allowing the polishing pad 10 and the surface 11 to be polished to be more accurately measured. It makes it possible to measure the polishing load acting in between.

  Two sets of differential transformers 3 constituting the expansion / contraction measuring means are fixed to the housing 9 and face the core 4 fixed to the tool shaft 1. The indentation length of the tool shaft 1 to the leaf spring 5 is determined by measuring the displacement of the two cores 4 arranged above and below the expansion / contraction connecting portion constituted by the leaf spring 5 and the leaf spring support 6. measure. By taking the difference in displacement between the two cores 4, it is possible to eliminate the influence of pushing the leaf spring support 6 into the rotation driving means 7. Therefore, it is possible to measure the indentation length of the tool shaft 1 into the leaf spring 5 with higher accuracy, and to measure the polishing load acting between the polishing pad 10 and the surface 11 to be polished with higher accuracy. The method for measuring the polishing load and the polishing process are the same as those in the first embodiment.

DESCRIPTION OF SYMBOLS 1 Tool axis | shaft 2 Fluid bearing 3 Differential transformer 4 Core 5 Leaf spring 6 Leaf spring support 7 Rotation drive means 8 Displacement mechanism 9 Case 10 Polishing pad 11 Polishing surface 12 Calculation means 13 Control means

Claims (3)

In a polishing apparatus that polishes a surface to be polished with a rotating polishing tool,
The polishing tool;
A tool shaft that holds the polishing tool and is movable in a thrust direction;
Rotation driving means for driving the tool shaft to rotate;
Load applying means for applying a load in the thrust direction to the polishing tool via the tool shaft;
An expansion / contraction connecting portion that connects the rotation driving means and the tool shaft so as to be extendable and contractible in the thrust direction, and transmits rotational torque generated by the rotation driving means to the tool shaft;
Expansion / contraction measuring means for measuring the expansion / contraction length of the expansion / contraction connection part;
An arithmetic means for calculating a polishing load when polishing the surface to be polished by the polishing tool from the expansion / contraction length of the expansion / contraction connecting portion,
And a control means for controlling the load applying means in accordance with the output of the calculating means.   The polishing apparatus according to claim 1, wherein the expansion / contraction measuring unit includes a differential transformer that measures the expansion / contraction length of the expansion / contraction coupling portion in a non-contact manner.   The polishing apparatus according to claim 1, wherein the control unit controls the load applying unit so as to reduce a change in the polishing load calculated by the calculation unit.

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