Double-ended surface grinding machine

Abstract

To enable detection of small cracks occurring in a workpiece and wear occurring in a stopper mechanism and reduction of costs.SOLUTION: A double head surface grinding device 1 includes: a moving mechanism 8 which causes first and second workpiece holders 10, 20 to close toward support positions; a stopper mechanism 9 which restricts the closing motion of the first and second workpiece holders 10, 20 by the moving mechanism 8 so that the first and second workpiece holders 10, 20 are positioned at the support positions; a distance sensor 102 which detects the relative distance between the first and second workpiece holders 10, 20; and a controller 100. The controller 100 compares the detection value of the relative distance in a state that the first and second workpiece holders 10, 20 are closed with a first threshold value and determines that a foreign object is sandwiched between a workpiece W and the first and second workpiece holders 10, 20 to stop grinding of the workpiece W when the relative distance is larger than the first threshold value.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present disclosure relates to a double-sided surface grinding apparatus.

Background Art

[0002] Patent Document 1 discloses an example of a double-sided surface grinding apparatus. Specifically, the apparatus disclosed in Patent Document 1 includes first and second work holders that non-contact support a thin plate-shaped work by the pressure of a fluid, and a pair of grinding wheels that grind both surfaces of the work supported by the first and second work holders.

[0003] Furthermore, the apparatus disclosed in Patent Document 1 includes a slide drive mechanism that slides the first and second work holders, and a stopper bolt and a stopper block. Here, the slide drive mechanism is a mechanism that brings the first and second work holders closer to each other toward a support position (grinding position) where the work is non-contact supported. The stopper bolt and the stopper block achieve accurate positioning by abutting against each other when the first and second work holders are brought close to the support position.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, when grinding thin, plate-shaped workpieces, slight chipping can occur due to material defects or abnormalities during grinding. If these fragments remain and the grinding process moves on to the next workpiece, there is a possibility that the fragments from the previous grinding operation will become lodged between the workpiece and the grinding wheel. Until now, while technologies for detecting relatively large damage such as cracks and fractures of workpieces have been known, such technologies have been insufficient to detect slight chipping.

[0006] One possible method for detecting minor defects is to image the workpiece using an image sensor. However, image sensors are generally expensive. Furthermore, using an image sensor requires the installation of new lighting equipment to clearly distinguish between light and dark areas, as well as a background, which is inconvenient for cost reduction.

[0007] Similar challenges exist in stopper mechanisms, which consist of stopper bolts and stopper blocks. In other words, wear can occur in the stopper mechanism as a large number of workpieces are ground. Conventional methods have been insufficient to achieve both the detection of such wear and cost reduction.

[0008] This disclosure has been made in view of the above, and its purpose is to achieve both the detection of slight chipping on the workpiece or wear on the stopper mechanism during the previous grinding, and cost reduction. [Means for solving the problem]

[0009] A first aspect of the present disclosure relates to a double-ended surface grinding apparatus comprising: first and second workpiece holders that non-contact support a thin plate-shaped workpiece by fluid pressure at a support position determined to sandwich the workpiece; and a pair of grinding wheels that grind the surfaces to be ground on both sides of the workpiece supported by the first and second workpiece holders. The double-ended surface grinding apparatus comprises: a moving mechanism that closes the first and second workpiece holders toward the support position; a stopper mechanism that restricts the closing of the first and second workpiece holders by the moving mechanism so that the first and second workpiece holders are positioned at the support position; a distance sensor that detects the relative distance between the first and second workpiece holders; and a controller to which the detection signal from the distance sensor is input.

[0010] Furthermore, according to the first embodiment, the controller sets a reference value for the relative distance achieved when the closing movement is restricted by the stopper mechanism and the first and second workpiece holders are in the support position, and a predetermined value set to be greater than the reference value as the first threshold. Based on the detection signal of the distance sensor, the controller compares the detected value of the relative distance when the first and second workpiece holders are in the closed position with the first threshold. If the relative distance is greater than the first threshold, the controller assumes that foreign matter is caught between the workpiece and the first or second workpiece holder and stops grinding the workpiece.

[0011] When the first and second workpiece holders are positioned at the desired support positions, the detected relative distance is expected to match the reference value. On the other hand, if a small chip occurs in the workpiece, there is a possibility that the fragment may stick to the first or second workpiece holder and remain there. In this case, if the grinding of the next workpiece proceeds with the fragment remaining, the detected value is expected to be larger than the reference value by the thickness of the fragment.

[0012] Therefore, according to the first embodiment, the controller compares the detected value with a first threshold value that is set to be larger than the reference value. By performing such a comparison, it becomes possible to detect chips that occurred in the workpiece during the previous grinding. Furthermore, the first embodiment does not require expensive sensors such as image sensors. Therefore, the first embodiment can achieve both the detection of slight chips that occurred in the workpiece during the previous grinding and cost reduction.

[0013] A second aspect of the present disclosure relates to a double-ended surface grinding apparatus comprising: first and second workpiece holders that non-contact support a thin plate-shaped workpiece by fluid pressure at a support position determined to sandwich the workpiece; and a pair of grinding wheels that grind the surfaces to be ground on both sides of the workpiece supported by the first and second workpiece holders. The double-ended surface grinding apparatus comprises: a moving mechanism that closes the first and second workpiece holders toward the support position; a stopper mechanism that restricts the closing of the first and second workpiece holders by the moving mechanism so that the first and second workpiece holders are positioned at the support position; a distance sensor that detects the relative distance between the first and second workpiece holders; and a controller to which the detection signal from the distance sensor is input.

[0014] Furthermore, according to the second embodiment, the relative distance achieved when the closing movement is restricted by the stopper mechanism and the first and second workpiece holders are in the support position is set as a reference value, and a predetermined value set to be smaller than the reference value is set as a second threshold. Based on the detection signal of the distance sensor, the controller compares the detected value of the relative distance when the first and second workpiece holders are in the closed position with the second threshold, and if the relative distance is smaller than the second threshold, it is determined that wear has occurred in the stopper mechanism, and grinding of the workpiece is stopped.

[0015] When the first and second workpiece holders are positioned at the desired support positions, the detected relative distance is expected to coincide with the reference value as described above. On the other hand, if wear occurs in the stopper mechanism, the detected value is expected to become smaller than the reference value depending on the amount of wear.

[0016] Therefore, according to the second embodiment, the controller compares the detected value with a second threshold value set to be smaller than the reference value. By performing such a comparison, it becomes possible to detect that wear has occurred in the stopper mechanism. Furthermore, the second embodiment does not require dedicated sensors such as linear scales for detecting the positions of the first and second workpiece holders. Therefore, the second embodiment can achieve both the detection of wear in the stopper mechanism and cost reduction.

[0017] A third aspect of the present disclosure relates to a double-ended surface grinding apparatus comprising: first and second workpiece holders that non-contact support a thin plate-shaped workpiece by fluid pressure at a support position determined to sandwich the workpiece; and a pair of grinding wheels that grind the surfaces to be ground on both sides of the workpiece supported by the first and second workpiece holders. The double-ended surface grinding apparatus comprises: a moving mechanism that closes the first and second workpiece holders toward the support position; a stopper mechanism that restricts the closing of the first and second workpiece holders by the moving mechanism so that the first and second workpiece holders are positioned at the support position; a distance sensor that detects the relative distance between the first and second workpiece holders; and a controller to which the detection signal from the distance sensor is input.

[0018] Furthermore, according to the third embodiment, the relative distance achieved when the closing movement is restricted by the stopper mechanism and the first and second workpiece holders are in the support position is set as a reference value, a predetermined value set to be greater than the reference value is set as the first threshold, and a predetermined value set to be less than the reference value is set as the second threshold. Based on the detection signal of the distance sensor, the controller compares the detected value of the relative distance when the first and second workpiece holders are in the closed position with the first threshold. If the relative distance is greater than the first threshold, grinding of the workpiece is stopped, assuming that foreign matter is caught between the workpiece and the first or second workpiece holder. On the other hand, if the relative distance is less than the second threshold, grinding of the workpiece is stopped, assuming that wear is occurring in the stopper mechanism.

[0019] When the first and second workpiece holders are positioned at the desired support positions, the detected relative distance is expected to match the reference value. On the other hand, if a small chip occurs in the workpiece, there is a possibility that the fragment may stick to the first or second workpiece holder and remain there. In this case, if the grinding of the next workpiece proceeds with the fragment remaining, the detected value is expected to be larger than the reference value by the thickness of the fragment. Furthermore, if wear occurs in the stopper mechanism, the detected value is expected to be smaller than the reference value depending on the amount of wear.

[0020] Therefore, according to the third embodiment, the controller compares the detected value with a first threshold set to be greater than a reference value, or compares the detected value with a second threshold set to be less than a reference value. By performing such comparisons, it becomes possible to detect chips in the workpiece or wear in the stopper mechanism. Furthermore, the third embodiment does not require expensive sensors such as image sensors. Therefore, the third embodiment, like the first and second embodiments, can achieve both the detection of slight chips in the workpiece or wear in the stopper mechanism and cost reduction.

[0021] Further, according to the fourth aspect of the present disclosure, each of the first and second work holders includes a base that slides as the moving mechanism operates, and a pad that is disposed on an end surface of the base and supports the work in a non-contact manner. The stopper mechanism includes a plurality of members disposed between the bases of the first and second work holders so as to surround the pads of the first and second work holders respectively. The distance sensor is disposed adjacent to at least one of the plurality of stopper mechanisms, and a distance between the distance sensor and the adjacent stopper mechanism may be shorter than a distance between the distance sensor and a central portion of the pad.

[0022] According to the fourth aspect, the distance sensor is disposed closer to at least one stopper mechanism than to the central portion of the pad. When the base is tilted, the detected value of the distance sensor changes significantly near the stopper mechanism. Therefore, by disposing the distance sensor near the stopper mechanism, even a slight tilt can be reliably detected. This is advantageous in ensuring the detection accuracy of chipping or wear.

Advantages of the Invention

[0023] As described above, according to the present disclosure, it is possible to achieve both detection of slight chipping occurring on the work or wear occurring on the stopper mechanism and cost reduction.

Brief Description of the Drawings

[0024] [Figure 1] It is a plan view illustrating the configuration of the double-sided surface grinding apparatus. [Figure 2] It is a front sectional view of the double-sided surface grinding apparatus. [Figure 3] It is a side sectional view of the double-sided surface grinding apparatus. [Figure 4] It is a schematic diagram for explaining the reference position. [Figure 5] It is a schematic diagram for explaining the support position. [Figure 6]This is a block diagram illustrating a configuration related to the controller. [Figure 7] This is a flowchart illustrating the first and second processes. [Figure 8] This is a diagram illustrating the trapping of foreign objects. [Figure 9] This is a diagram illustrating the wear of the stopper mechanism. [Figure 10] Figure 7 is a corresponding diagram showing a modified example of the processing performed by the controller. [Figure 11] Figure 7 is a corresponding diagram showing a modified example of the processing performed by the controller. [Modes for carrying out the invention]

[0025] The embodiments of this disclosure will be described below with reference to the drawings. Note that the following description is illustrative.

[0026] (Overall structure) Figure 1 is a plan view illustrating the configuration of the double-ended surface grinding machine 1. Figure 2 is a front cross-sectional view of the double-ended surface grinding machine 1, corresponding to the view taken by arrow AA in Figure 1. Figure 3 is a side cross-sectional view of the double-ended surface grinding machine 1, corresponding to the view taken by arrow BB in Figure 1. Figure 4 is a schematic diagram illustrating the reference position, and Figure 5 is a schematic diagram illustrating the support position. Figure 6 is a block diagram illustrating the configuration related to the controller 100.

[0027] As shown in Figure 1, the double-ended surface grinding apparatus 1 comprises first and second workpiece holders 10 and 20, and a first grinding wheel 31 and a second grinding wheel 32. The first and second workpiece holders 10 and 20 non-contact support the workpiece W by fluid pressure at a predetermined "support position". The first and second grinding wheels 31 and 32 grind the surfaces to be ground on both sides of the workpiece W supported by the first and second workpiece holders 10 and 20, and constitute a "pair of grinding wheels" in this embodiment.

[0028] The term "support position" here refers to a position determined to hold a thin plate-shaped workpiece W in a non-contact manner, as shown in Figure 5. Furthermore, the non-contact support achieved at the "support position" can be rephrased as "static pressure support." The workpiece W may be a thin, disc-shaped object to be ground, such as a semiconductor wafer.

[0029] Specifically, the double-ended surface grinding apparatus 1 comprises a work drive apparatus 2 having the first and second work holders 10 and 20, a grinding wheel apparatus 3 having a pair of grinding wheels consisting of a first grinding wheel 31 and a second grinding wheel 32, and a controller 100.

[0030] (Work drive device) The work drive device 2 is a device that holds and rotates a workpiece W when grinding both sides of the workpiece W. This work drive device 2 comprises a case 5, a workpiece holding mechanism 6, a workpiece rotation mechanism 7, a moving mechanism 8, and a stopper mechanism 9.

[0031] Here, case 5 surrounds the workpiece holding mechanism 6 and supports the workpiece holding mechanism 6 within case 5 so that it can move relative to it. Case 5 is formed, for example, in the shape of a roughly rectangular box with openings at the top and bottom.

[0032] The workpiece holding mechanism 6 holds the workpiece W from both sides. The workpiece holding mechanism 6 has a first workpiece holder 10 and a second workpiece holder 20. The first workpiece holder 10 holds the workpiece W from one side, front or back. The second workpiece holder 20 holds the workpiece W from the other side, front or back. The first and second workpiece holders 10 and 20 are arranged facing each other and are supported by the case 5 so as to be movable in the left-right direction.

[0033] The first and second workpiece holders 10 and 20 each have a base 11 and 21 that slides in conjunction with the operation of the moving mechanism 8, and pads 12 and 22 that are positioned on the end faces of the bases 11 and 21 respectively and provide non-contact support for the workpiece W.

[0034] Specifically, the first workpiece holder 10 includes a reference base 11 arranged parallel to a vertical plane in the front-rear direction, and a reference pad 12 provided on the end face of the reference base 11 on the side of the second workpiece holder 20.

[0035] The second workpiece holder 20 includes a pressurizing base 21 arranged parallel to a vertical plane in the front-rear direction, and a pressurizing pad 22 provided on the end face of the pressurizing base 21 on the side of the first workpiece holder 10.

[0036] The reference pad 12 and the pressure-side pad 22 are designed to provide non-contact support to the workpiece W from both sides by the pressure of a fluid, such as water pressure, and are formed in a substantially disc shape. Discharge ports (not shown) for discharging fluid are opened on the opposing surfaces of the reference pad 12 and the pressure-side pad 22.

[0037] The reference pad 12 and the pressure pad 22 are provided with arc-shaped first notches 61 corresponding to the first and second grinding wheels 31 and 32, respectively, extending from their outer edges to a position slightly beyond the centers of the reference base 11 and the pressure base 21 (see Figures 2 and 3).

[0038] The reference base 11 and the pressure-side base 21 are each composed of a substantially rectangular plate with thickness in the left-right direction. On the lower side of the reference base 11 and the pressure-side base 21, an arc-shaped second notch 62 corresponding to the first notch 61 is provided, extending from its outer edge to a position slightly beyond the center of the reference base 11 and the pressure-side base 21 (shown only in Figure 2).

[0039] Furthermore, four support rollers 63 surrounding the reference pad 12 are arranged on the surface of the reference base 11 facing the pressurizing base 21. These four support rollers 63 rotatably support the carrier 60 that holds the workpiece W.

[0040] The carrier 60 is formed in a ring shape that allows the workpiece W to be loosely fitted. The inner circumferential surface of the carrier 60 is provided with a projection (not shown) that protrudes radially inward. This projection is configured to engage with a notch (not shown) provided on the outer circumferential surface of the workpiece W. This engagement causes the workpiece W to rotate in conjunction with the rotation of the carrier 60.

[0041] The workpiece rotation mechanism 7 rotates the workpiece W held by the workpiece holding mechanism 6. This workpiece rotation mechanism 7 includes a carrier drive motor 71 and a carrier drive shaft 72.

[0042] The carrier drive motor 71 is connected to the carrier drive shaft 72. When the carrier drive motor 71 is activated, its rotational force rotates the carrier drive shaft 72. The carrier drive shaft 72 has a carrier drive gear (not shown) at its tip. When the carrier drive shaft 72 rotates, its rotational force rotates the carrier 60 via the carrier drive gear. As the carrier 60 rotates, the workpiece W also rotates as described above.

[0043] The moving mechanism 8 closes the first and second workpiece holders 10 and 20 toward the "support position" for achieving static pressure support. This closing operation is achieved by sliding the workpiece holder mechanism 6 relative to the case 5. In this embodiment, this sliding operation corresponds to movement along the left-right direction in Figures 1 and 2, and Figures 3 and 4. Furthermore, the closing operation of the first and second workpiece holders 10 and 20 is an operation that brings the first workpiece holder 10 and the second workpiece holder 20 closer to each other. To achieve such an operation, the moving mechanism 8 according to this embodiment has a plurality of guide bars 81, a plurality of bushings 82, a reference side cylinder 83, and a pressurizing side cylinder 84.

[0044] Each of the multiple guide bars 81 extends horizontally within the case 5 and penetrates the first workpiece holder 10 and the second workpiece holder 20 in the horizontal direction. The multiple guide bars 81 support the first workpiece holder 10 and the second workpiece holder 20 so that they can slide freely in the horizontal direction. In this embodiment, a total of four guide bars 81 are installed in the case 5, one each in the front, back, top, and bottom.

[0045] The multiple bushes 82 are interposed members between each guide bar 81 and the through holes of the first and second workpiece holders 10 and 20 through which each guide bar 81 is inserted. Each guide bar 81 is slidably inserted through each through hole of the first and second workpiece holders 10 and 20 via each bush 82. This allows the first and second workpiece holders 10 and 20 to slide left and right along each guide bar 81. Each bush 82 may be, for example, a double bush.

[0046] The reference cylinder 83 moves the first workpiece holder 10 relative to the case 5 and the second workpiece holder 20. The pressurizing cylinder 84 moves the second workpiece holder 20 relative to the case 5 and the first workpiece holder 10. The reference cylinder 83 and the pressurizing cylinder 84 may be, for example, pneumatic cylinders, so-called air cylinders.

[0047] The moving mechanism 8 brings the first workpiece holder 10 and the second workpiece holder 20 close enough to the workpiece W that they do not come into direct contact with it during grinding of the workpiece W. At that time, the first workpiece holder 10 and the second workpiece holder 20 will be positioned at the desired "support position" shown in Figure 5, provided that no foreign matter is caught between them, the stopper mechanism 9 is worn, etc.

[0048] When the workpiece W is replaced, the moving mechanism 8 moves the second workpiece holder 20 apart from the first workpiece holder 10 in the left-right direction. At that time, the first workpiece holder 10 is maintained in the desired "reference position" shown in Figure 4.

[0049] The aforementioned "support position" can be considered as the relative positional relationship achieved when the first workpiece holder 10 is positioned at the "reference position" and the second workpiece holder 20 is brought closer to the desired position, as shown in Figure 5.

[0050] The stopper mechanism 9 is a mechanism that restricts the closing movement of the first and second workpiece holders 10 and 20 by the moving mechanism 8 so that the first and second workpiece holders 10 and 20 are positioned in the "support position".

[0051] Multiple stopper mechanisms 9 are provided between the bases 11 and 21 of the first and second workpiece holders 10 and 20, respectively, so as to surround the pads 12 and 22 of the first and second workpiece holders 10 and 20, respectively. For example, as shown in Figure 3, the stopper mechanisms 9 according to this embodiment are arranged at each of the four corners (particularly the four corners in the front-rear and up-down directions) between the first and second workpiece holders 10 and 20.

[0052] Furthermore, each of the multiple (four in this embodiment) stopper mechanisms 9 includes multiple (four in this embodiment) reference-side bolts 91, the same number of pressure-side bolts 92 as the reference-side bolts 91, and the same number of stopper blocks 93 as the reference-side bolts 91.

[0053] As shown in Figures 1 and 2, each reference bolt 91 is fixed to the four corners of the first workpiece holder 10, particularly the reference base 11. As schematically shown in Figures 4 and 5, each reference bolt 91 has a bolt head 91a that protrudes to the left, i.e., toward the second workpiece holder 20. The amount of protrusion of the bolt head 91a is adjustable.

[0054] As shown in Figures 1 and 2, each pressure-side bolt 92 is fixed to the four corners of the second workpiece holder 20, particularly the pressure-side base 21. As schematically shown in Figures 4 and 5, each pressure-side bolt 92 has a bolt head 92a that protrudes to the right, i.e., toward the first workpiece holder 10. The amount of protrusion of the bolt head 92a is adjustable.

[0055] As shown in Figures 1 to 3, each stopper block 93 is fixed to one of the four corners of the case 5. And, as schematically shown in Figures 4 and 5, each stopper block 93 has a reference-side stop pin 93a that protrudes opposite to the corresponding reference-side bolt 91 and a pressure-side stop pin 93b that protrudes opposite to the corresponding pressure-side bolt 92.

[0056] As shown in Figure 4, when the first workpiece holder 10 is in the "reference position", the stopper block 93 and the reference bolt 91 come into contact. More specifically, when the first workpiece holder 10 is in the "reference position", the reference stop pin 93a and the bolt head 91a of the reference bolt 91 come into contact.

[0057] As shown in Figure 5, when the first workpiece holder 10 and the second workpiece holder 20 are in the "support position", the stopper block 93 and the reference side bolt 91 come into contact with each other, and the stopper block 93 and the pressure side bolt 92 come into contact with each other. More specifically, when the first workpiece holder 10 and the second workpiece holder 20 are in the "support position", the reference side stop pin 93a and the bolt head 91a of the reference side bolt 91 come into contact with each other, and the pressure side stop pin 93b and the bolt head 92a of the pressure side bolt 92 come into contact with each other.

[0058] Then, at the "support position," the workpiece W is supported without contact between the reference pad 12 and the pressure pad 22. Considering that it is supported without contact, the actual distance (predetermined distance X) between the reference pad 12 and the pressure pad 22 at the "support position" is at least greater than the thickness D of the workpiece W.

[0059] To detect that the "reference position" and the "support position" have been achieved, the double-ended surface grinding machine 1 is further equipped with a reference sensor 101 and a distance sensor 102.

[0060] The reference sensor 101 detects the position of the first workpiece holder 10 relative to the stopper block 93. In this embodiment, the reference sensor 101 is fixed to the stopper block 93 and detects the distance of the first workpiece holder 10 to the stopper block 93 in the left-right direction. The reference sensor 101 is electrically connected to the controller 100 by wire or wireless connection and inputs an electrical signal indicating the detection result to the controller 100. This electrical signal can be used to determine whether or not the first workpiece holder 10 is located at the "reference position".

[0061] The distance sensor 102 is used to detect the relative distance between the first and second workpiece holders 10 and 20. More specifically, the distance sensor 102 is provided on one of the first and second workpiece holders 10 and 20 and detects the relative distance between it and the other of the first and second workpiece holders 10 and 20.

[0062] More specifically, the distance sensor 102 is provided on the first workpiece holder 10 and detects the relative distance between the first workpiece holder 10 and the second workpiece holder 20. The distance sensor 102 may be, for example, an eddy current type distance sensor.

[0063] Specifically, as shown in Figure 3, the distance sensor 102 according to this embodiment is positioned adjacent to one of the multiple stopper mechanisms 9 (in the illustrated example, the stopper mechanism 9 located above and behind). Here, the distance between the distance sensor 102 and the stopper mechanism 9 adjacent to the distance sensor 102 is shorter than the distance between the distance sensor 102 and the central part C of the reference side pad 12.

[0064] The relative distance detected by the distance sensor 102 may be the distance between the reference pad 12 and the pressure pad 22, or the distance between the reference base 11 and the pressure base 21.

[0065] Furthermore, if the distance sensor 102 is attached to the first workpiece holder 10, the distance may be defined as the distance between the distance sensor 102 and the pressurized base 21 or the pressurized pad 22. Similarly, if the distance sensor 102 is attached to the second workpiece holder 20, the distance may be defined as the distance between the distance sensor 102 and the reference base 11 or the reference pad 12.

[0066] For example, the distance sensor 102 according to this embodiment is fixed to the reference side base 11 of the first workpiece holder 10. The distance sensor 102 according to this embodiment detects the distance between the distance sensor 102 and the pressurized side base 21 of the second workpiece holder 20.

[0067] The distance sensor 102 is electrically connected to the controller 100 by wire or wireless connection and inputs an electrical signal indicating its detection result to the controller 100. This electrical signal can be used in combination with the detection signal from the reference sensor 101 to determine whether the first workpiece holder 10 and the second workpiece holder 20 are located in the "support position".

[0068] (Grinding device) The grinding wheel device 3 is a device that grinds both sides of a workpiece W, which is held and rotated by the work drive device 2, using first and second grinding wheels 31 and 32. The first grinding wheel 31 moves back and forth through the first notch 61 and the second notch 62 of the first workpiece holder 10. The second grinding wheel 32 moves back and forth through the first notch 61 and the second notch 62 of the second workpiece holder 20.

[0069] The grinding wheel device 3 comprises cup-shaped first and second grinding wheels 31 and 32, and a grinding wheel drive motor 33 that rotates the grinding wheels 31 and 32. The grinding wheel device 3 is located on both the left and right sides of the work drive device 2. The grinding wheel drive motor 33 is shown only in Figure 6.

[0070] The first and second grinding wheels 31 and 32 are positioned to face both sides of the workpiece W held by the carrier 60, via the first and second notches 61 and 62 of the first workpiece holder 10 and the second workpiece holder 20, respectively.

[0071] Specifically, the first grinding wheel 31 is positioned to face one side (for example, the right side) of the workpiece W held by the carrier 60 via the first and second notches 61 and 62 of the first workpiece holder 10.

[0072] On the other hand, the second grinding wheel 32 is positioned to face the other side (for example, the left side) of the workpiece W held by the carrier 60 via the first and second notches 61 and 62 of the second workpiece holder 20.

[0073] Furthermore, the grinding device 3 is configured to allow the first and second grinding wheels 31 and 32 to move in the axial direction (left and right direction), and when the workpiece W is replaced, the first and second grinding wheels 31 and 32 are moved from the "grinding position" to a predetermined "standby position".

[0074] (controller) The controller 100 has a CPU, memory, and input / output bus, and is configured, for example, as a CNC machine. As shown in Figure 6, the controller 100 is electrically connected by wire or wireless to the carrier drive motor 71, the reference side cylinder 83, the pressurizing side cylinder 84, and the grinding wheel drive motor 33. More specifically, the reference side cylinder 83 and the pressurizing side cylinder 84 are electrically connected via electromagnetic switching valves (not shown).

[0075] When grinding the workpiece W, the controller 100 positions the first and second grinding wheels 31 and 32 in the "standby position" and opens the second workpiece holder 20 while holding the first workpiece holder 10 in the "reference position". The workpiece W is mounted onto the carrier 60 via the space between the first workpiece holder 10 and the second workpiece holder 20 by a loader (not shown) (see Figures 1 and 3).

[0076] When the workpiece W is mounted on the carrier 60, the controller 100 activates the pressurizing cylinder 84 to move the second workpiece holder 20 toward the first workpiece holder 10, positioning it in a "support position" where the reference pad 12 and the pressurizing pad 22 are in close proximity to both sides of the workpiece W.

[0077] The controller 100 then discharges fluids such as air or water from the discharge ports of the reference pad 12 and the pressurizing pad 22, respectively. As a result, the workpiece W is held in a non-contact state by receiving fluid pressure from both sides.

[0078] As described above, with the workpiece W held in place, the controller 100 activates the carrier drive motor 71 to rotate the carrier 60. This rotation also causes the workpiece W to start rotating. The controller 100 also activates the grinding wheel drive motor 33 to rotate the first and second grinding wheels 31 and 32. While rotating the first and second grinding wheels 31 and 32, the controller 100 gradually moves the first and second grinding wheels 31 and 32 closer to the grinding surface of the workpiece W from the "standby position". This approach causes the workpiece W to be sandwiched on both sides by the first and second grinding wheels 31 and 32, which are in the "grinding position". This initiates the grinding of the workpiece W.

[0079] When grinding of the workpiece W is complete, the controller 100 moves the first and second grinding wheels 31 and 32 from the "grinding position" to the "standby position," and also moves the second workpiece holder 20 from the "support position." The ground workpiece W is removed from the carrier 60 and transported away by a loader (not shown).

[0080] As mentioned above, the controller 100 is electrically connected to both the reference sensor 101 and the distance sensor 102. The controller 100 receives detection signals (electrical signals) from the reference sensor 101 and the distance sensor 102.

[0081] The controller 100 can determine whether the first workpiece holder 10 is in the "reference position" based on the detection signal from the reference sensor 101. The controller 100 can also determine whether the first and second workpiece holders 10 and 20 are in the "support position" based on the detection signal from the distance sensor 102.

[0082] Furthermore, the controller 100 detects the relative distance between the first and second workpiece holders 10 and 20 based on the detection signal from the distance sensor 102, as described above. In particular, the controller 100 according to this embodiment detects the relative distance between the reference pad 12 and the pressure-side pad 22.

[0083] Furthermore, relative distance detection can be performed, for example, by considering the relative position of the distance sensor 102 with respect to the reference base 11, and the left-right thickness of the reference pad 12 and the pressure pad 22, respectively, in the detection value of the distance sensor 102.

[0084] Furthermore, the detected relative distance referred to here may be the actual distance between the reference pad 12 and the pressure pad 22, or it may not be the actual distance.

[0085] For example, when calculating the length of the former, the relative position of the distance sensor 102 with respect to the reference base 11 may be added to the detected value of the distance sensor 102, and the thickness of the reference pad 12 and the pressure pad 22 in the left-right direction may be subtracted from this added value to obtain the detected relative distance value.

[0086] On the other hand, when using the latter length, the detected relative distance may be a relative value relative to the relative distance (a predetermined distance X in Figure 5) achieved when the closing movement of the first and second workpiece holders 10 and 20 is restricted by the stopper mechanism 9 and the first and second workpiece holders 10 and 20 are in a desired "support position".

[0087] In the latter case, as illustrated in Figure 5, when the first and second workpiece holders 10 and 20 are in the desired "support position", there is a predetermined distance X between the first workpiece holder 10 and the second workpiece holder 20. However, in the process described below, the magnitude of the deviation from the predetermined distance X is treated as the "detected relative distance".

[0088] For example, using the definition of the predetermined distance X described above, if the relative distance between the first and second workpiece holders 10 and 20 is "X + ΔX", then the value of "ΔX" rather than the value of "X + ΔX" itself can be treated as the detected relative distance. In this embodiment, such a value of "ΔX" (relative value from a reference value) is used as the detected relative distance.

[0089] For example, in this embodiment, when the first and second workpiece holders 10 and 20 are located at the "support position," the detected relative distance becomes "zero" (ΔX = 0 as defined above). Also, when the first and second workpiece holders 10 and 20 are closer than the "support position," the detected relative distance becomes a "negative value." Also, when the first and second workpiece holders 10 and 20 are further apart than the "support position," the detected relative distance becomes a "positive value."

[0090] The processing performed by the controller 100 consists of at least one of the following: a first process for detecting that a foreign object M has been caught in addition to the workpiece W at the "support position"; and a second process for detecting that wear has occurred in the stopper mechanism 9, also at the "support position".

[0091] In this case, when a thin plate-shaped workpiece W is used for grinding, the workpiece W may chip slightly due to defects in the material or abnormalities that occur during grinding. If the grinding of the next workpiece W is started while these fragments remain, there is a possibility that the fragments from the previous workpiece may get stuck between the workpiece W and the grinding wheels 31 and 32. The foreign matter M referred to here is foreign matter such as these fragments.

[0092] It is not mandatory for the controller 100 to perform at least one of the first and second processes. A separate controller from the grinding controller 100 may be provided, and that controller may be made to perform at least one of the first and second processes, or to perform various other processes. The "various processes" referred to here include processes for discharging fluid, processes for determining whether the first workpiece holder 10 is in the "reference position", etc.

[0093] The controller 100 uses the "reference value" as a parameter common to the first and second processes. The controller 100 uses a predetermined first threshold as a parameter specific to the first process. The controller 100 uses a predetermined second threshold as a parameter specific to the second process. The values ​​of the reference value, the first threshold, and the second threshold may be read into the controller 100 from an external source, or they may be stored in the controller 100's memory or elsewhere beforehand.

[0094] Here, the "first threshold" is a predetermined value set to be at least greater than the "reference value," and the "second threshold" is a predetermined value set to be at least less than the "reference value."

[0095] Both the first and second processes are performed when the first and second workpiece holders 10 and 20 are closed toward the "support position" during grinding of the workpiece W. Both the first and second processes detect whether or not the first and second workpiece holders 10 and 20 have been positioned at the desired "support position".

[0096] The first process detects a situation in which the first and second workpiece holders 10 and 20 were moved to the "support position" but the closing motion stopped while the first and second workpiece holders 10 and 20 were actually separated from the "support position".

[0097] The second process detects a situation where, although the first and second workpiece holders 10 and 20 are moved to the "support position," they have actually come closer to the "support position."

[0098] The details of the first and second processes are described below.

[0099] (Details of the first and second processes) Figure 7 is a flowchart illustrating the first and second processes. Figure 8 is a diagram illustrating the trapping of foreign matter M, and Figure 9 is a diagram illustrating the wear of the stopper mechanism 9.

[0100] First, in step S1 of Figure 7, the controller 100 reads the detection signal from the distance sensor 102.

[0101] In the subsequent step S2, the controller 100 detects the relative distance between the first and second workpiece holders 10 and 20 based on the detection signal from the distance sensor 102. As described above, the detected relative distance in this embodiment corresponds to a relative value based on the state when the first and second workpiece holders 10 and 20 are in the desired "support position". This detected value corresponds to the value when the first and second workpiece holders 10 and 20 are closed. When acquiring the relative distance, it is not necessary to consider whether the "support position" is actually achieved or not. Situations in which the "support position" is not actually achieved include the situation in which a foreign object M is caught, as shown in Figure 8, and the situation in which wear occurs in the stopper mechanism 9, as shown in Figure 9.

[0102] In the subsequent step S3, the controller 100 compares the detected relative distance with a first threshold, and also compares the detected value with a second threshold.

[0103] In the following step S4, the controller 100 determines whether the detected relative distance is greater than the first threshold. If the determination is NO, the controller 100 proceeds to step S5 of the control process.

[0104] On the other hand, if the determination in step S4 is YES, it is considered that a foreign object M is trapped between the workpiece W and the first or second workpiece holder 10, 20, as shown in Figure 8, for example. In this case, as is clear from comparing Figure 5 and Figure 8, the distance between the reference pad 12 and the pressure pad 22 becomes longer than the predetermined distance X achieved at the desired "support position" (see ΔX1>0 in Figure 8). In this case, non-contact support is not necessarily maintained, and if grinding is performed in this state, there is a concern that the workpiece W and the first and second grinding wheels 31, 32 may be damaged.

[0105] As mentioned above, when the relative value from a predetermined distance X is set as the detected value of the distance sensor 102, the detected value referenced in step S4 corresponds to the value of the deviation ΔX1 in Figure 8. If this deviation ΔX1 is greater than the first threshold, the determination in step S4 becomes YES. In this case, the controller 100 assumes that a foreign object M is caught between the workpiece W and the first or second workpiece holder 10, 20, and proceeds to step S6 of the control process, stopping the grinding of the workpiece W.

[0106] Furthermore, assuming that fragments resulting from chipping of the workpiece W become foreign matter M, the thickness (horizontal dimension) of this foreign matter M is thought to reach a maximum of approximately the thickness D of the workpiece W. In that case, the actual distance X' between the reference side pad 12 and the pressure side pad 22 can be assumed to reach approximately twice the thickness D, taking both the workpiece W and the foreign matter M into consideration.

[0107] The deviation ΔX1 under these assumptions is: ΔX1 = X' - X = 2 × DX …(1) This is the result.

[0108] The first threshold value according to this embodiment is set to be smaller than the right-hand side of equation (1). For example, if the predetermined distance X = 1000 [μm] and the thickness D = 800 [μm], the right-hand side of equation (1) becomes 600 [μm]. To make it smaller than this value, for example, the first threshold value is set to 500 [μm].

[0109] By setting the first threshold to be smaller than the right-hand side of equation (1), it becomes possible to detect when a foreign object M with a thickness smaller than the thickness D of the workpiece W is trapped inside. This enables more accurate detection.

[0110] Furthermore, in step S5, the controller 100 determines whether the detected relative distance is smaller than the second threshold. If this determination is NO, the controller 100 proceeds to step S7 and continues grinding the workpiece W.

[0111] On the other hand, if the determination in step S5 is YES, it is considered that wear has occurred in at least one of the reference bolt 91, pressure bolt 92, and stopper block 93 that constitute the stopper mechanism 9, as shown in Figure 9 for example. Figure 9 illustrates a state in which the pressure stop pin 93b has worn down. In this case, as is clear from comparing Figure 5 and Figure 9, the distance between the reference pad 12 and the pressure pad 22 becomes shorter than the predetermined distance X achieved at the desired "support position" (see ΔX2<0 in Figure 9). In this case, normal non-contact support may not be maintained, and if grinding is performed in this state, there is a concern that the machining accuracy will deteriorate and the first and second grinding wheels 31 and 32 will be damaged. In other words, because the stopper mechanism 9 has worn down, the workpiece holders 10 and 20 that come into contact with it may tilt or the distance between the pads may narrow, which may disrupt the balance of static pressure holding of the workpiece W and worsen the machining accuracy.

[0112] As described above, when the relative value from a predetermined distance X is set as the detected value of the distance sensor 102, the detected value referenced in step S5 corresponds to the value of the deviation ΔX2 in Figure 9. If this deviation ΔX2 is smaller than the second threshold, the determination in step S5 becomes YES. In this case, the controller 100 assumes that wear has occurred in at least a part of the stopper mechanism 9, proceeds to step S6 of the control process, and stops grinding the workpiece W.

[0113] Thus, according to the above embodiment, as shown in steps S3 to S4 of Figure 7, the controller 100 compares the detected value of the distance sensor 102 with a first threshold value that is set to be larger than the reference value. By performing such a comparison, it becomes possible to detect foreign matter M caused by chipping of the workpiece W.

[0114] Furthermore, as shown in steps S3 and S5 of Figure 7, the controller 100 compares the detected value of the distance sensor 102 with a second threshold value set to be smaller than the reference value. By performing such a comparison, it becomes possible to detect that wear has occurred in the stopper mechanism 9.

[0115] Furthermore, this configuration does not require expensive sensors such as image sensors. Therefore, the above embodiment can achieve both the detection of slight chipping in the workpiece or the detection of wear in the stopper mechanism 9, and cost reduction.

[0116] Furthermore, as shown in Figure 3, the distance sensor 102 is positioned close to a stopper mechanism 9 located above and behind the central part C of the reference pad 12. If the reference base 11 tilts, the detected value of the distance sensor 102 will change significantly near the stopper mechanism 9. Therefore, by positioning the distance sensor 102 near the stopper mechanism 9, even slight tilts can be reliably detected. This is advantageous in ensuring the accuracy of detecting chipping or wear.

[0117] <Other Embodiments> Figures 10 and 11 are corresponding diagrams to Figure 7, showing modified examples of the processing performed by the controller 100. The flowchart in Figure 7 and the flowchart in Figure 10 differ only in the presence or absence of step S5. Similarly, the flowchart in Figure 7 and the flowchart in Figure 11 differ only in the presence or absence of step S4.

[0118] As mentioned above, it is not mandatory for the controller 100 to perform both the first and second processes; it may perform only the first process as shown in Figure 10, or only the second process as shown in Figure 11. [Explanation of Symbols]

[0119] 1. Double-ended surface grinding machine 10. First workpiece holder 11. Reference Base (Base) 12. Reference side pad (pad) 20 Second workpiece holder 21 Pressurized base (base) 22 Pressure side pad (pad) 31. First grinding wheel (a pair of grinding wheels) 32. Second grinding wheel (a pair of grinding wheels) 8 Moving mechanism 9. Stopper mechanism 100 controllers 102 Distance Sensor Double job M Foreign object

Claims

1. A double-ended surface grinding apparatus comprising: first and second workpiece holders that non-contact support a thin plate-shaped workpiece by fluid pressure at support positions determined to sandwich the workpiece; and a pair of grinding wheels that grind the surfaces to be ground on both sides of the workpiece supported by the first and second workpiece holders, A moving mechanism for closing the first and second workpiece holders toward the aforementioned support position, A stopper mechanism that restricts the closing movement of the first and second workpiece holders by the moving mechanism so that the first and second workpiece holders are positioned at the support position, A distance sensor for detecting the relative distance between the first and second workpiece holders, The system includes a controller to which the detection signal from the distance sensor is input, If the relative distance achieved when the closing movement is restricted by the stopper mechanism and the first and second workpiece holders are in the support position is taken as the reference value, and a predetermined value set to be greater than the reference value is taken as the first threshold value, Based on the detection signal from the distance sensor, the controller: The detected relative distance in the state in which the first and second workpiece holders are closed is compared with the first threshold value. If the relative distance is greater than the first threshold, it is assumed that foreign matter is trapped between the workpiece and the first or second workpiece holder, and the grinding of the workpiece is stopped. A double-ended surface grinding device characterized by the following features.

2. A double-ended surface grinding apparatus comprising: first and second workpiece holders that non-contact support a thin plate-shaped workpiece by fluid pressure at support positions determined to sandwich the workpiece; and a pair of grinding wheels that grind the surfaces to be ground on both sides of the workpiece supported by the first and second workpiece holders, A moving mechanism for closing the first and second workpiece holders toward the aforementioned support position, A stopper mechanism that restricts the closing movement of the first and second workpiece holders by the moving mechanism so that the first and second workpiece holders are positioned at the support position, A distance sensor for detecting the relative distance between the first and second workpiece holders, The system includes a controller to which the detection signal from the distance sensor is input, If the relative distance achieved when the closing movement is restricted by the stopper mechanism and the first and second workpiece holders are in the support position is taken as the reference value, and a predetermined value set to be smaller than the reference value is taken as the second threshold value, Based on the detection signal from the distance sensor, the controller: The detected relative distance in the state in which the first and second workpiece holders are closed is compared with the second threshold value. If the relative distance is smaller than the second threshold, wear is assumed to be occurring in the stopper mechanism, and the grinding of the workpiece is stopped. A double-ended surface grinding device characterized by the following features.

3. A double-ended surface grinding apparatus comprising: first and second workpiece holders that non-contact support a thin plate-shaped workpiece by fluid pressure at support positions determined to sandwich the workpiece; and a pair of grinding wheels that grind the surfaces to be ground on both sides of the workpiece supported by the first and second workpiece holders, A moving mechanism for closing the first and second workpiece holders toward the aforementioned support position, A stopper mechanism that restricts the closing movement of the first and second workpiece holders by the moving mechanism so that the first and second workpiece holders are positioned at the support position, A distance sensor for detecting the relative distance between the first and second workpiece holders, The system includes a controller to which the detection signal from the distance sensor is input, If the relative distance achieved when the closing movement is restricted by the stopper mechanism and the first and second workpiece holders are in the support position is taken as the reference value, a predetermined value set to be greater than the reference value is set as the first threshold value, and a predetermined value set to be less than the reference value is set as the second threshold value, Based on the detection signal from the distance sensor, the controller: The detected relative distance in the state in which the first and second workpiece holders are closed is compared with the first threshold value. When the relative distance is greater than the first threshold, grinding of the workpiece is stopped, assuming that a foreign object is trapped between the workpiece and the first or second workpiece holder. When the relative distance is smaller than the second threshold, the grinding of the workpiece is stopped, assuming that wear is occurring in the stopper mechanism. A double-ended surface grinding device characterized by the following features.

4. In a double-ended surface grinding apparatus according to any one of claims 1 to 3, The first and second workpiece holders are, A base that slides along with the operation of the aforementioned moving mechanism, The base has a pad positioned on the end face of the base and providing non-contact support for the workpiece, The stopper mechanism is arranged in multiple locations between the bases of the first and second workpiece holders so as to surround the pads of the first and second workpiece holders, The distance sensor is positioned adjacent to at least one of the plurality of stopper mechanisms. The distance between the distance sensor and the stopper mechanism adjacent to the distance sensor is shorter than the distance between the distance sensor and the center of the pad. A double-ended surface grinding device characterized by the following features.

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