JP5891010B2 - Thin plate workpiece grinding method and double-head surface grinding machine - Google Patents

Description

  The present invention relates to a method for grinding a thin plate workpiece used when grinding a thin plate workpiece such as a silicon wafer, and a double-head surface grinder.

  When grinding both sides of a thin plate workpiece such as a silicon wafer with a pair of grinding wheels using a double-head surface grinder, measure the thickness of the workpiece being ground by a measuring means having a pair of measuring heads, In-process sizing grinding is employed in which the measured value is controlled to coincide with the grinding reference value and finished to a predetermined dimensional accuracy (Patent Document 1).

For example, in the case of grinding the master work the same thickness, by measuring the thickness of the master work by previously not a measurement unit to determine the thickness of the master workpiece and the grinding reference value under the grinding environment Zeroing. When grinding an actual workpiece, the thickness of the workpiece is measured by the same measuring means during grinding, and when the measured value coincides with the zeroed grinding reference value, it shifts to spark out, After continuing the spark-out for a certain time, the grinding wheel is moved backward to finish grinding.

JP 2003-71713 A

  By adopting such in-process sizing grinding, the workpiece can be ground in the same grinding environment as the master workpiece, so that the workpiece can be finished to the same thickness as the master workpiece. However, if there is a difference in the sharpness of both grinding wheels, there will be a large difference in the finished state of both sides of the workpiece, and there is a drawback that the predetermined grinding accuracy cannot be stably maintained over a long period of time.

  That is, in a double-sided surface grinder, when a workpiece held statically by a pair of hydrostatic pads is ground from both sides by a pair of grinding wheels, rough grinding, intermediate grinding and finish grinding are performed as shown in FIG. After that, the workpiece is ground to a predetermined grinding accuracy. In this case, it is very important that the sharpness of the pair of grinding wheels is always the same during the grinding of the workpiece at the time when higher accuracy of grinding is required.

  When the sharpness of the pair of grinding wheels is equal, the machining allowance of each workpiece by the grinding wheels is the same as shown by the solid line in FIG. However, since there is variation in the amount of wear of each grinding wheel in an actual grinding wheel, if the grinding wheel is used for a long period of time, a great difference occurs in the sharpness of the grinding wheel due to the difference in the amount of grinding wheel wear.

  In a grinding wheel having a large grinding wheel wear amount, the self-generated action of the abrasive grains is sustained and the sharpness is good, so that the machining allowance increases as shown by a one-dot chain line in FIG. On the other hand, in a grinding wheel with a small grinding wheel wear amount, the sharpness is poor due to clogging between the abrasive grains, etc., so that the machining allowance is reduced as shown by a two-dot chain line in FIG. As a result, even if the workpiece finish dimensions are the same, there is a great difference in the finished state of both sides of the workpiece due to the difference in the sharpness of the grinding wheel.

  The surface of the workpiece ground with a sharp grinding wheel becomes rough, and the surface of the workpiece ground with a grinding wheel with poor sharpness has a mirror-like surface close to polishing. Occurs. If the workpiece in such a ground state is left as it is, due to the difference in surface area between the rough surface side and the mirror surface side of the workpiece, the rough surface side with a large surface area becomes the outside and the mirror surface side with a small surface area becomes the inside. There is a risk of warping.

  In addition, when a workpiece is ground with a grinding wheel with different sharpness, even if the workpiece itself has a predetermined finish thickness, stress corresponding to the difference in machining allowance is applied to both sides of the workpiece, and both sides of the workpiece are removed. Therefore, there is a problem that if the stress or damage is large, the grinding accuracy deviates from the reference value and becomes a defective product.

  Furthermore, since the workpiece between a pair of static pressure pads is normally held horizontally by holding water supplied from the holding surface side of each static pressure pad, the ideal grinding position of the workpiece is the center between the static pressure pads. I want to grind that position as the grinding reference position. However, when looking at the material shape of a workpiece such as an actual silicon wafer, it is not necessarily a perfect flat surface such as a warped side, and the thickness is uneven, so that the grinding accuracy such as flatness is within the standard value The position of the workpiece does not become the center between the hydrostatic pads, which may affect the sharpness of the left and right grinding wheels.

  In spite of the great sharpness caused by the difference in the amount of grinding wheel wear between the grinding wheels, the grinding accuracy of the workpiece is greatly affected. It is very difficult to adjust the grinding conditions of both grinding wheels so that the sharpness of both grinding wheels is always the same in accordance with the factors of the grinding wheel wear. Therefore, in conventional grinding of silicon wafers and the like, there is a problem that many defective products are generated due to variation in sharpness caused by the difference in grinding wheel wear amount of each grinding wheel, resulting in an increase in product cost and a decrease in yield. is there.

  In view of such conventional problems, the present invention can eliminate differences in sharpness due to differences in the amount of grinding wheel wear of each grinding wheel as much as possible, and can grind thin plate workpieces that can stably maintain a predetermined grinding accuracy over a long period of time. It is an object to provide a method and a double-head surface grinder.

The thin plate workpiece grinding method according to the present invention comprises a pair of grindings that move both side surfaces of a thin plate workpiece held between a pair of hydrostatic pads from a grinding back end to a grinding advance end at substantially the same speed at substantially the same speed. When grinding with a grindstone, determine the relative position between the hydrostatic pads of the workpiece being ground and compare the relative position of the workpiece being ground with the grinding reference position where the workpiece between the hydrostatic pads should be properly held. When there is a difference between them, the grinding back end of the grinding wheel is corrected according to the difference between the two after grinding the workpiece so that the grinding advance end of both grinding wheels coincides with the grinding reference position at the next grinding. Is.

  The position of the workpiece when the grinding accuracy of the workpiece being ground is within the reference accuracy may be set as the relative position. The position of the workpiece when the grinding accuracy of the workpiece is within the reference accuracy in the prior grinding may be set as the grinding reference position, and this grinding reference position may be fixedly set. The position of the workpiece when the zero signal indicating the workpiece sizing from the sizing device in prior grinding is received as the grinding reference position, and the workpiece position when the zero signal is received from the sizing device in the main grinding is the relative position. It is also good.

  The relative position and the grinding reference position may be compared to calculate a deviation amount and a deviation direction of the relative position with respect to the grinding reference position, and the grinding backward end of the grinding wheel may be corrected based on the deviation amount and the deviation direction. Calculate the absolute position between the static pressure pads of the workpiece when the grinding accuracy of the workpiece is within the reference accuracy in advance grinding, and set the grinding reference position when this absolute position is less than the threshold determined by the grinding accuracy. May be.

The double-sided surface grinding machine according to the present invention includes a pair of grinding wheels that move both side surfaces of a thin plate-like workpiece held between a pair of hydrostatic pads substantially simultaneously at substantially the same speed from a grinding back end to a grinding forward end. In the double-sided surface grinder to be ground, grinding is performed based on the measurement values of the pair of measuring heads that measure the positions of both sides of the workpiece being ground and the measurement head when the grinding accuracy of the workpiece being grounded is within the reference accuracy. The calculation means for obtaining the relative position between the static pressure pads of the workpiece in the middle, the relative position of the workpiece during grinding, and the grinding reference position where the workpiece between the static pressure pads should be properly held are obtained to obtain the difference. When there is a difference between the position comparison means and the both, the grinding wheel retreats according to the difference between the two after grinding the workpiece so that the grinding advance end of both grinding wheels coincides with the grinding reference position at the next grinding. Correct edges It is obtained by a Shisatan correction means.

According to the present invention, the relative position of the workpiece being ground is calculated, the relative position is compared with a grinding reference position where the workpiece should be properly held, and if there is a difference between the two, The grinding wheel wear of a pair of grinding wheels that grind both sides of the workpiece to correct the grinding back end of the grinding wheel according to the difference between the workpiece after grinding so that the grinding advance end of the grinding wheel matches the grinding reference position The difference in amount can be eliminated as much as possible, and a predetermined grinding accuracy can be stably maintained over a long period of time. Therefore, there is an advantage that the workpiece grinding accuracy can be improved, the product cost can be reduced, and the yield can be improved.

It is a plane lineblock diagram of a horizontal type double head surface grinding machine showing a 1st embodiment of the present invention. It is the same side view. It is a block diagram of the control system. It is explanatory drawing of the display means. It is explanatory drawing of the same position measuring method. It is planar sectional drawing of the jig | tool etc. for the same position measurement. It is a side view of the jig | tool for the same position measurement. It is explanatory drawing of the same position measuring method. It is a flowchart figure at the time of the same test grinding. It is a flowchart figure at the time of the same grinding. It is explanatory drawing of the same sharpness difference. It is a block diagram which shows the 2nd Embodiment of this invention. It is explanatory drawing of the flow volume adjustment of the grinding water. It is explanatory drawing of the machining allowance by the difference in the sharpness of a grinding wheel.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 to 11 illustrate a horizontal double-sided surface grinder adopting the present invention. As shown in FIGS. 1 and 2, the horizontal double-head surface grinding machine includes a pair of left and right static pressure pads 1 and 2 that are arranged opposite to each other and hold a thin plate-like workpiece W, and each static pressure pad 1. A pair of left and right grinding wheels 5 for grinding the left and right side surfaces of the workpiece W, which are rotatably arranged around the left and right axial centers corresponding to the concave portions 3 and 4 of the two, and are held by the static pressure pads 1 and 2. , 6, a carrier (not shown) that rotates the workpiece W held by the static pressure pads 1, 2 around the center, and the left and right sides of the workpiece W corresponding to the notches 7, 8 of the static pressure pads 1, 2. A pair of left and right measuring heads 9 and 10 are provided on both sides.

  The static pressure pads 1 and 2 are movable in the left-right direction between an advanced position for holding the workpiece W and a retracted position for retracting from the workpiece W, and the holding is supplied to the holding surface facing the workpiece W at the advanced position. The workpiece W is statically held via a holding fluid such as water.

  The grinding wheels 5 and 6 are cup-shaped or the like and are provided at the tips of the grinding wheel shafts 13 and 14 rotatably supported by the bearing boxes 11 and 12, and are driven to rotate by the grinding wheel drive motors 15 and 16. The bearing housings 11 and 12 are supported by a sliding guide mechanism (not shown) so as to be movable in the left-right direction, and driven by a cutting shaft drive motor (not shown) to provide a cutting shaft (not shown), a sliding guide mechanism, and the like. The grinding wheels 5 and 6 are moved in the left-right direction between the grinding forward end and the grinding backward end.

  The measuring heads 9 and 10 measure the positions of both side surfaces of the workpiece W, and are supported by the support member 17 on the fixed side via the pivotal support portions 9a and 10a so as to be swingable. Is configured to output an electrical signal corresponding to the angular displacement around the pivotal support portions 9a and 10a of the measuring heads 9 and 10 when they contact the side surface of the workpiece W. The measuring heads 9 and 10 can also measure the positions of the static pressure pads 1 and 2 via the workpiece W that contacts the static pressure pads 1 and 2.

  Each measuring head 9, 10 constitutes a part of a sizing device 18 for in-process sizing grinding, and its output end side is connected to an amplifier 19. The sizing device 18 is connected to the grinding control device 20. The sizing device 18 outputs a zero signal when the grinding accuracy of the workpiece W falls within the reference accuracy during grinding (for example, when the workpiece W reaches a predetermined thickness), and the grinding operation of the grinding control device 20 is performed. Under the control of the control means 21, a predetermined operation such as a spark out is shifted.

  As shown in FIG. 3, the grinding control device 20 includes measured values M <b> 1 and M <b> 1 from the measurement heads 9 and 10 in addition to the conventionally known grinding operation control means 21 that controls a series of grinding operations from insertion to removal of the workpiece W. The position calculation means 22 for calculating the position of the workpiece W in real time based on M2, and the relative position X of the workpiece W when the grinding accuracy of the workpiece W is within the reference accuracy in preliminary grinding such as trial grinding of the workpiece W. Is determined as a grinding reference position X0 which is a grinding target at the time of main grinding, and a grinding reference position setting means 23 for zeroing (stored in a storage means), and a workpiece W calculated by the position calculating means 22 at the time of main grinding of each workpiece W. The relative position X of the workpiece W is compared with the already stored grinding reference position X0 to obtain the difference between them (the positional deviation between them), the relative position X of the workpiece W and the grinding reference position X0. When the next grinding, the grinding advance ends of the grinding wheels 5 and 6 coincide (measured values M1 and M2 from the measuring heads 9 and 10 when the grinding wheels 5 and 6 advance to the grinding advance end) To match the reference values M1r and M2r on both sides of the workpiece W when the grinding reference position X0 is determined), after the grinding of the workpiece W, the grinding back ends of the grinding wheels 5 and 6 are set according to the difference. The back end correcting means 25 for correcting, the measured values M1, M2 on both sides of the workpiece W from the measuring heads 9, 10, and the reference values M1r, M2r on both sides of the workpiece W when the grinding reference position X0 is determined. Subtraction is performed to calculate the positions R1 and R2 on both sides of the workpiece W, and the difference between the positions R1 and R2 on both sides is compared in real time and the difference is calculated. Based on the difference in the wear amount of the grinding wheel. In this case, when there is a sharpness difference between the grinding wheels 5 and 6, the grinding wheel 5 and the grinding wheel 5 and 6 have the same sharpness. , 6 the grinding condition correction means 27 for correcting the grinding conditions related to the sharpness of the grinding wheels 5 and 6, the change in the relative position X of the workpiece W with respect to the grinding reference position X0, both side surfaces of the workpiece W Display means 28 for displaying the positions R1, R2, etc., and is constituted by a microcomputer including a ROM, a RAM, a CPU and the like.

  In addition, by comparing the positions R1 and R2 on both sides of the workpiece W in real time, in addition to the amount of grinding wheel wear on both grinding wheels 5 and 6 due to the difference between the positions R1 and R2 on both sides, 6 can also calculate the total machining allowance of the workpiece W.

  As shown in FIG. 4, the display means 28 includes a relative position display unit 29 for displaying the relative position X of the workpiece W in a bar graph, and a workpiece position display unit 30 for displaying the positions R1, R2 on the left and right side surfaces of the workpiece W in a bar graph. 31. The relative position display section 29 is horizontally long and long in the left-right direction. The relative position display section 29 is provided with a predetermined scale in the left-right direction around the zeroed grinding reference position X0, and is relative to the grinding reference position X0. A change in the relative position X of the workpiece W is displayed by an indicator 29a such as a pointer.

  The work position display units 30 and 31 are vertically long and long in the vertical direction, and are arranged side by side corresponding to the left and right side surfaces of the work W. Each workpiece position display unit 30, 31 is provided with a predetermined scale in the vertical direction, and positions R1, R2 on both side surfaces of the workpiece W are displayed by instruction units 30a, 31a extending from the bottom to the top (or from the top to the bottom). It is like that. The directions of the relative position display unit 29 and the work position display units 30 and 31 are arbitrary, and the relative position display unit 29 and the work position display units 30 and 31 are the relative position X and the positions R1 and R1 on both sides of the work W. R2 may be displayed as a numerical value. Further, the display means 28 has a display unit (not shown) for displaying each information described later as required.

  During grinding of a workpiece W such as a silicon wafer by a double-sided surface grinder, slight abrasive grains are dropped due to wear of the grinding wheels 5 and 6, the shape of the workpiece W is slightly different, and the workpiece W and a pair of hydrostatic pads 1. , 2 due to the effect of subtle changes in the water film between the two and two, especially the variation of the grinding wheel wear amount of the grinding wheels 5 and 6, the sharpness of the grinding wheels 5 and 6, the relative position X of the workpiece W, the workpiece Positions R1 and R2 on both side surfaces of W change from moment to moment.

  However, a relative position display unit 29 and workpiece position display units 30 and 31 are provided on the display means 28, the relative position display unit 29 displays the relative position X of the workpiece W, and the workpiece position display units 30 and 31 display the workpiece W. By displaying the positions R1 and R2 of the both side surfaces, the sharpness of the grinding wheels 5 and 6, the relative position X of the workpiece W, and the changes in the positions R1 and R2 of the both sides of the workpiece W can be visualized.

  The position calculating means 22 includes a pinch determination unit 34 that determines whether the grindstone 5 or 6 is pinched by the grinding wheel 5 or 6 based on an increase in load current of the grindstone drive motors 15 or 16, a decrease in rotational speed, or the like. A position calculation unit 35 that takes in the measurement values M1 and M2 from the measurement heads 9 and 10 and calculates the relative position X of the workpiece W between the static pressure pads 1 and 2;

  Using the fact that the thickness T of the workpiece W is known, the pinching determination unit 34 appropriately sets the timing for monitoring the position of the workpiece W as a grinding condition, and the timing comes after the start of the grinding cycle. It may be determined whether the workpiece W is caught by the grindstones 5 and 6. The position calculator 35 is based on the measured values M1 and M2 from the measuring heads 9 and 10, and the absolute position Xabs, which is the absolute position of the workpiece W with respect to the center position between the static pressure pads 1 and 2, and the static pressure pads 1 and 2. The grinding reference position X0 where the workpiece W should be properly held in between and the relative position X of the workpiece W held between the static pressure pads 1 and 2 are calculated and stored as needed.

  The grinding reference position setting means 23 includes a zeroing unit 36 for zeroing the grinding reference position X0, a reference position determination unit 37 for determining whether the grinding reference position X0 is appropriate based on the absolute value | Xabs | of the absolute position Xabs, Have

  When the grinding accuracy of the workpiece W falls within the reference accuracy in the preliminary grinding such as trial grinding, for example, when the zero signal output from the sizing device 18 is received, the zeroing unit 36 receives each measurement head 9 at that time, The relative position X calculated based on the ten measurement values M1 and M2 is read from the position calculation unit 35, and the relative position X is zeroed as a grinding reference position X0 which is a grinding target. Therefore, the relative position display unit 29 sets the grinding reference position X0 to zero, and displays the change in the relative position X during the grinding of the workpiece W with respect to the grinding reference position X0 by the position in the left-right direction of the instruction unit 29a.

  The reference position determination unit 37 reads the absolute position Xabs between the static pressure pads 1 and 2 of the workpiece W when zeroing the grinding reference position X0 calculated by the position calculation unit 35, and the absolute value | Xabs | Is determined to be less than a preset threshold value according to the grinding accuracy. For example, if the absolute value | Xabs | is less than the threshold value, the display means 28 is within the grinding reference position setting range. When the zeroing of the grinding reference position X0 is completed and the absolute value | Xabs | is equal to or greater than the threshold value, the display means 28 appropriately displays that the grinding reference position is out of the setting range. Encourage confirmation and adjustment of accuracy.

When the grinding accuracy of the workpiece W falls within the reference accuracy for each grinding of the main grinding, for example, when the zero signal output from the sizing device 18 is received, the position comparison means 24 receives each measuring head 9 at that time, The relative position X calculated by the position calculation unit 35 based on the ten measurement values M1 and M2 is read, and the relative position X is compared with the grinding reference position X0, and the difference between the relative position X and the grinding reference position X0 is compared. The presence / absence of (position misalignment) is determined. The position comparison means 24 calculates the deviation direction and the deviation amount of the relative position X of the workpiece W with respect to the grinding reference position X0.

  When there is a difference between the relative position X of the workpiece W and the grinding reference position X0 by the calculation of the position comparison means 24, the backward end correcting means 25 is the next time after the end of the spark-out that is performed for a certain time from the reception of the zero signal. According to the displacement direction and the displacement amount of the relative position X of the workpiece W so that the grinding advance ends of the grinding wheels 5 and 6 coincide with the reference values M1r and M2r of the both sides of the workpiece W at the grinding reference position X0 during grinding. The grinding backward end of the cutting shaft, that is, the grinding backward end of the grinding wheels 5 and 6 is corrected.

  The fixed time from the start to the end of the spark out is determined according to the grinding conditions. Further, the positions (reference values M1r, M2r) on both sides of the workpiece W at the grinding reference position X0 mean the grinding advance ends of the grinding wheels 5, 6. The correction of the grinding back end of the cutting shaft, that is, the grinding back end of the grinding wheels 5 and 6 functions as one of the sharpness control of the grinding wheels 5 and 6, so the other of the pair of grinding wheels 5 and 6 is used as a reference. May be corrected, or both may be corrected in the opposite direction.

  The sharpness comparison means 26 subtracts the measured values M1 and M2 from the measuring heads 9 and 10 and the reference values M1r and M2r on both sides of the workpiece W at the grinding reference position X0 to obtain the positions R1 and R2 on both sides of the workpiece W. The difference between the grinding wheel wear amounts of the grinding wheels 5 and 6 is calculated by comparing the difference between the workpiece position calculation unit 41 to be calculated and the positions R1 and R2 on both sides of the workpiece W, and the difference in the grinding wheel wear amount is calculated. And a sharpness determination unit 42 that determines the sharpness difference based on the difference. The sharpness determining unit 42 calculates the sharpness difference between the grinding wheels 5 and 6 and the correction direction. The positions R1 and R2 on both sides of the workpiece W calculated by the workpiece position calculation unit 41 are displayed as changes in the instruction units 30a and 31a of the workpiece position display units 30 and 31.

  The grinding condition correction means 27 includes an occasional correction unit 39 that corrects the grinding conditions as needed in real time so that the sharpness difference between the grinding wheels 5 and 6 is eliminated during grinding, and both in preparation for the next grinding after the workpiece W has been ground. A post-correction unit 40 that post-corrects the grinding conditions so as to eliminate the difference in sharpness between the grinding wheels 5 and 6 is provided.

  As needed, the correction unit 39 has grinding conditions that do not affect the grinding accuracy so as to eliminate the sharpness difference between the grinding wheels 5 and 6 according to the sharpness difference between the grinding wheels 5 and 6 calculated in real time by the sharpness comparison means 26. For example, the flow rate of the grinding water (grinding fluid) supplied between the grinding wheels 5 and 6 and the static pressure pads 1 and 2 from the center side of the grinding wheels 5 and 6 is controlled.

  The post-correction unit 40 performs both grinding wheels 5 and 5 according to the sharpness difference between the grinding wheels 5 and 6 at the time of receiving the zero signal after the spark-out that ends after a predetermined time from the reception of the zero signal determined by the grinding conditions. The grinding condition is controlled so that the difference in sharpness of 6 is eliminated. In this case, the correction of the grinding condition by the post-correction unit 40 is performed during grinding, whereas the correction in real time by the correction unit 39 is a flow control of the grinding water that does not affect the grinding accuracy. For example, it is control of grinding conditions that affect the grinding accuracy, for example, the number of revolutions of the grinding wheels 5 and 6 and / or the cutting speed of the grinding wheels 5 and 6. In addition, correction | amendment of grinding conditions is performed based on the difference in the sharpness of each grinding wheel 5 and 6, and a correction direction.

  Next, calculation of the gap D between the static pressure pads 1 and 2 and recognition of the position of the workpiece W between the static pressure pads 1 and 2 will be described with reference to FIGS. As shown in FIG. 5A, when it is determined where the workpiece W inserted in the gap D between the left and right static pressure pads 1 and 2 is located in the gap D, the measuring heads 9 and 10 are in advance. Measure the position of the static pressure pads 1 and 2 and store the measured values A1 and B2.

  In this case, since the measuring heads 9 and 10 cannot directly measure the positions of the static pressure pads 1 and 2 due to their structures, the measurement is performed by the following method. For example, a workpiece W having a known thickness T is arranged between the static pressure pads 1 and 2 as shown in FIG. 5A, and the measured values M1 and M2 of the measuring heads 9 and 10 are read. Next, as shown in FIG. 5B, the measured values A1 and A2 of the measuring heads 9 and 10 when the work W is brought into contact with the left static pressure pad 1 are read, and further as shown in FIG. 5C. The measured values B1 and B2 of the measuring heads 9 and 10 when the workpiece W is brought into contact with the right static pressure pad 2 are read and stored.

  The positions of the left and right static pressure pads 1 and 2 can be calculated if the measured values of the left and right measuring heads 9 and 10 can be grasped. For example, when the measured value M2 of the right measuring head 10 is used as a reference (hereinafter referred to as the right), the work W is brought into contact with the right static pressure pad 2 as shown in FIG. When the measured value of the measuring head 10 is B2, and the measured value of the right measuring head 10 when the workpiece W is brought into contact with the left hydrostatic pad 1 as shown in FIG. 5B is A2. Since the thickness T of the workpiece W is known, the position of the left static pressure pad 1 is A2-T, and the gap D between the left and right static pressure pads 1 and 2 is expressed by the equation D = B2- (A2-T ). This measurement may be performed after the installation of the machine or after the replacement of the static pressure pads 1 and 2 and does not have to be performed every normal grinding.

  When the static pressure pads 1 and 2 attract and deliver the workpiece W by the vacuuming means when the workpiece W is carried in / out, the workpiece W is transferred to the static pressure pad 1 using the vacuuming means. , 2 may be adsorbed. However, of the pair of static pressure pads 1 and 2, for example, the right static pressure pad 2 has a evacuation means, but the left static pressure pad 1 has no evacuation means. Using a jig 43 configured as shown in FIG. 7, a plate 44 with a known thickness T is mounted on the left hydrostatic pad 1, and the measuring elements 9b and 10b of the measuring heads 9 and 10 are brought into contact with the plate 44. And measure it.

  The jig 43 includes a plate-like main body portion 45 that is detachably fitted to the cutout portion 7 of the static pressure pad 1 from the outside in the radial direction, and the left static pressure pad 1 from the inner end side of the main body portion 45. It has the standing part 46 which stands to the back side, and the support part 47 which protrudes in the both sides of the notch part 7 from the outer end side of the main-body part 45. As shown in FIG.

  A plate 44 that comes into contact with the holding surface 1a of the left hydrostatic pad 1 is detachably fixed to the main body 45 via a fixing tool 48 such as a pair of mounting screws. The standing portion 46 is provided with a contact portion 49, and the contact portion 49 is urged by a spring or the like to elastically contact the back side of the left hydrostatic pad 1. Each support portion 47 is detachably fixed to the main body portion 45 via a fixing tool 50 such as a mounting screw. At both ends of the support portion 47, contact portions 51 that are urged by a spring or the like and elastically contact the right static pressure pad 2 are provided. The body portion 45 is provided with an opening 52 so that the measuring elements 9 b and 10 b come into contact with the plate 44.

  When the plate 44 is attached to the left hydrostatic pad 1 via the jig 43, the main body portion is arranged so that the outer peripheral edge of the plate 44 is in contact with or close to the holding surface 1a of the left hydrostatic pad 1. 45 is inserted into the notch 7 of the left hydrostatic pad 1. Then, the contact portion 49 of the standing portion 46 is brought into contact with the back surface of the static pressure pad 1, and the jig 43 and the plate 44 are attached to the left static pressure pad 1 by the pressing force. Thereafter, when the two static pressure pads 1 and 2 are brought close to each other, the contact portion 51 of the support portion 47 presses against the right static pressure pad 2, and both the static pressure pads 1 and 2 sandwich the plate 44. As shown in FIG. 7, the outer peripheral edge of the plate 44 can be fixed along the holding surface 1 a of the left hydrostatic pad 1.

  After the plate 44 is mounted on the left static pressure pad 1 in this way, the measurement values of the measuring heads 9 and 10 are measured by bringing the measuring elements 9b and 10b into contact with both sides of the plate 44 as shown by a two-dot chain line in FIG. If M1 and M2 are read, the position of the left static pressure pad 1 having no vacuuming means can be easily measured.

  The position of the workpiece W between the static pressure pads 1 and 2 is recognized as follows. When an unground workpiece W is inserted between the static pressure pads 1 and 2, the workpiece W is held between the static pressure pads 1 and 2 as shown in FIG. The right gap D2 between the workpiece W and the right static pressure pad 2 at this time is the measured value M2 on the right side of the workpiece W in FIG. 8A and the workpiece as shown in FIG. 8B. From the measured value B2 of the measuring head 10 when W is in contact with the right static pressure pad 2, it can be obtained by the arithmetic expression D2 = B2-M2.

  Similarly, the left gap D1 between the workpiece W and the left static pressure pad 1 is also measured with the measured value M1 on the left side surface of the workpiece W in FIG. 8A and the workpiece as shown in FIG. From the measured value A1 of the measuring head 9 when W comes into contact with the left static pressure pad 1, it can be obtained by the arithmetic expression D1 = A1-M1.

  Accordingly, since the distances D1 and D2 from the workpiece W to the respective static pressure pads 1 and 2 are known, the position of the workpiece W between the respective static pressure pads 1 and 2, for example, the absolute position Xabs and the relative position X can be monitored. If D1 = D2, the workpiece W is located at the center between the static pressure pads 1 and 2.

  Next, a method for determining the grinding reference position X0 as a grinding target and zeroing the grinding reference position X0 will be described with reference to the flowchart of FIG. First, a workpiece W is inserted in trial grinding (step S1), and a grinding cycle is started (step S2). By starting the grinding cycle, the respective static pressure pads 1 and 2 advance to a predetermined position and hold the workpiece W by static pressure, and then the respective grinding wheels 5 and 6 advance to grind both side surfaces of the workpiece W. However, since the position of the workpiece W is unstable until both the grinding wheels 5 and 6 sandwich the workpiece W, the sandwiching determination unit 34 of the position calculating means 22 confirms that the workpiece W is sandwiched by the grinding wheels 5 and 6. (Step S3), the position calculation unit 35 takes in the measured values M1 and M2 of the measuring heads 9 and 10, and starts monitoring the position of the workpiece W (Step S4).

  When the position monitoring of the workpiece W starts, first, the position calculation unit 35 calculates the absolute position Xabs of the workpiece W with respect to the center position between the static pressure pads 1 and 2 (step S5), and displays the absolute position Xabs on the display means 28. (Step S6). The absolute position Xabs of the workpiece W can be calculated by (D2-D1) / 2. The position calculating unit 35 calculates the relative position X of the workpiece W (step S7), and if there are previously zeroed reference values M1r and M2r (step S8), the relative position with respect to the reference values M1r and M2r. X is calculated and displayed (step S9). The relative position X is calculated by an arithmetic expression {(M1-M1r)-(M2-M2r)} / 2. If there is no zeroed position, the measured values M1 and M2 of the measuring heads 9 and 10 are displayed as they are (steps S8 and S10).

  If the workpiece W for trial grinding has a predetermined thickness, there is a zero signal from the sizing device 18 (step S11), and spark-out is started by the zero signal (step S12). When the spark-out is started, the cutting shaft is stopped, and the measuring heads 9 and 10 are retracted from both side surfaces of the workpiece W. On the other hand, simultaneously with the start of spark-out, the relative position X of the workpiece W at the time of reception of the zero signal calculated by the position calculation unit 35 is read (step S13), and the zeroing unit 36 sets the relative position X as a grinding target. Zeroing is performed as the grinding reference position X0 (step S14), and the grinding reference position X0 is displayed as zero on the display means 28.

  Simultaneously with the start of spark out, the absolute position of the workpiece W between the static pressure pads 1 and 2 when the reference position determination unit 37 receives the zero signal calculated by the position calculation unit 35 (when the grinding reference position X0 is zeroed). The absolute value | Xabs | of the position Xabs is read and compared with a threshold set in advance based on the absolute value | Xabs | Is determined (step S15). If the absolute position Xabs of the workpiece W is less than the threshold value, it is displayed on the display means 28 as being within the grinding reference position setting range, and zeroing is completed (step S16). If the absolute value | Xabs | is equal to or greater than the threshold value, it is displayed on the display means 28 as out of the grinding reference position setting range (step S17), and prompts the operator to check accuracy and adjust accuracy.

  The zeroing of the grinding reference position X0 is performed simultaneously with the start of spark out. The spark-out is set in advance to a certain time based on the grinding conditions. When the spark-out is completed after the lapse of the certain time (steps S18 and S19), the cutting shaft moves to the grinding backward end (step S20). Since the grinding cycle is completed (step S21), the workpiece W after the trial grinding is taken out (step S22), the workpiece W after the grinding is artificially measured (step S23), and the grinding accuracy is determined (step). S24).

  If the predetermined grinding accuracy is not obtained as a result of the judgment of the grinding accuracy, or the zeroed grinding reference position X0 is out of the grinding reference position range, the accuracy adjustment is performed so that the predetermined grinding accuracy is obtained. Then, the work W is inserted again, and an appropriate grinding reference position X0 is determined and zeroed.

  Next, the position monitoring of the workpiece W and the sharpness control of the grinding wheels 5 and 6 in the main grinding will be described with reference to the flowchart of FIG. First, the workpiece W is inserted (step S30), and a grinding cycle is started (step S31). When the grinding cycle is started, after the pinching determination unit 34 confirms that the workpiece W is pinched by the grinding wheels 5 and 6 (step S32), the position calculation unit 35 measures the measured values M1 and M2 of the measuring heads 9 and 10 in real time. The position of the workpiece W is monitored while taking in (step S33).

  When the measurement values M1 and M2 of the measuring heads 9 and 10 are taken in, the position calculation unit 35 calculates the current relative position X of the workpiece W based on the measurement values M1 and M2 (step S34), and the zeroed grinding reference position. The current position with respect to X0 is displayed in real time by the pointer 29a or the like (step S35).

  At the same time, the sharpness comparison means 26 determines the difference in sharpness between the grinding wheels 5 and 6. That is, the reference values M1r and M2r on both sides of the workpiece W when the grinding reference position X0 is determined from the stored data are read (step S36), and the workpiece position calculation unit 41 determines the reference values M1r and M2r and the time point After calculating the positions R1 and R2 on both sides of the workpiece W with respect to the reference values M1r and M2r by subtracting the measured values M1 and M2 (step S37), the sharpness determining unit 42 determines the positions R1 and R2 on both sides. R2 is compared to calculate the difference in grinding wheel wear amount between both grinding wheels 5 and 6, and based on the difference in grinding wheel wear amount, it is determined whether there is a difference in sharpness between both grinding wheels 5 and 6 (step S38).

  For example, when the grinding wheel wear amount of the left grinding wheel 5 is smaller than the grinding wheel wear amount of the right grinding wheel 6 and the sharpness of the left grinding wheel 5 is worse than the sharpness of the right grinding wheel 6, grinding is performed. As shown in FIG. 11, the inner workpiece W2 is pushed rightward by the grinding wheel 5 with poor sharpness and moved to the grinding wheel 6 with good sharpness.

  Therefore, if the workpiece W2 being ground has a positional relationship as shown in FIG. 11 with respect to the workpiece W1 when the grinding reference position X0 is determined, the reference values M1r and M2r of the workpiece W1 and the measurement of the current workpiece W2 are performed. From the values M1 and M2, the left position R1 of the workpiece W2 can be calculated by the arithmetic expression R1 = M1-M1r, and the right position R2 can be calculated by the arithmetic expression R2 = M2-M2r.

  And by calculating | requiring the right-and-left difference (DELTA) R (= R1-R2) of position R1, R2 of the both sides | surfaces of the workpiece | work W, the magnitude | size of the sharpness difference of both the grinding stones 5 and 6 can be known, and at the same time, the worse one It can be seen which of the grinding wheels 5 and 6 is. In the case as shown in FIG. 11, ΔR <0, which indicates that the left grinding wheel 5 has poor sharpness. ΔR = 0 indicates that the sharpness of the grinding wheels 5 and 6 is equal. Further, ΔR> 0 is a case opposite to that in FIG. 11, and indicates that the right grinding wheel 6 has poor sharpness.

  If the sharpness determination result is ΔR <0 or ΔR> 0 (step S38), the grinding water that the correction unit 39 does not affect the grinding accuracy at any time so as to eliminate the sharpness difference between the grinding wheels 5 and 6 during grinding. Is corrected in real time (step S39). In this case, a control map in which the flow rate of the grinding water changes in accordance with the left-right difference ΔR and the correction direction (±) is created in advance, and the grinding water corresponding to the magnitude and positive / negative of the left-right difference ΔR based on the control map. It is desirable to change the flow rate. The adjustment of the flow rate of the grinding water may be continued until the sharpness of the grinding wheels 5 and 6 coincides or may be controlled based on the control map.

  The workpiece position display units 30 and 31 of the display means 28 display the positions R1 and R2 of both side surfaces at that time with reference to both side surfaces of the workpiece W at the grinding reference position X0 during grinding of the workpiece W. If the sharpness of the left and right grinding wheels 5 and 6 is substantially the same, the display of the work position display sections 30 and 31 of the display means 28 shows substantially the same level, and if the sharpness of the grinding wheels 5 and 6 is different, As shown in FIG. 4, the level corresponding to the sharpness difference is displayed.

  For example, in the case shown in FIG. 11, the level of the instruction unit 30 a of the work position display unit 30 is low as shown in FIG. The level of the instruction unit 31a increases. For this reason, if the display of the workpiece position display parts 30 and 31 is seen, the difference in the sharpness of the grinding wheels 5 and 6 can be easily grasped as a change in the positions R1 and R2 on both side surfaces of the workpiece W during grinding.

  As shown in FIG. 11, when the sharpness of the left grinding wheel 5 is poor, the flow rate of the grinding water supplied between the left grinding wheel 5 and the workpiece W is decreased according to the degree of sharpness. As a result, the discharge of the abrasive grains falling from the grinding wheel 5 is delayed, and the residence time of the abrasive grains between the grinding wheel 5 and the workpiece W is increased, so that the abrasive grains wear as a sharpening stone. Promotes sharpness. As a result, the difference in sharpness between the left and right grinding wheels 5 and 6 can be minimized.

  The flow rate of the grinding water on the sharp grinding wheels 5 and 6 side may be kept constant, the flow rate of the grinding water on the grinding wheels 5 and 6 side having poor sharpness may be reduced, and conversely the grinding wheel having poor sharpness. The flow rate of the grinding water on the 5th and 6th side may be kept constant, and the flow rate of the grinding water on the 5th and 6th side of the grinding wheel 5 and 6 having good sharpness may be increased. Further, the grinding water of both grinding wheels 5 and 6 is reduced, for example, by increasing the flow rate of grinding water on the grinding wheels 5 and 6 side with good sharpness and decreasing the flow rate of grinding water on the grinding wheels 5 and 6 side with poor sharpness. The flow rate may be increased or decreased.

  When the workpiece W reaches the target thickness, a zero signal is received from the sizing device 18 (step S40), the cutting axis is stopped, the measuring heads 9 and 10 are retracted, and spark out is started (step S41). . At the same time, the position comparison means 24 calculates the relative position X of the workpiece W at the time of reception of the zero signal calculated by the position calculation means 22 (step S42), and compares this with the grinding reference position X0 that is the grinding target to perform grinding. A displacement amount and a displacement direction of the workpiece W with respect to the reference position X0 are obtained (step S43). At the same time, from the measured values M1 and M2 when the zero signal is received, the left / right difference ΔR between the positions R1 and R2 on both sides of the workpiece W at that time is calculated (step S44). Prepare for correction of grinding back end.

  The spark-out is set in advance to a certain time based on the grinding conditions. When the certain time elapses, the spark-out is completed (steps S45 and S46), and when the grinding cycle ends and the grinding of the workpiece W ends ( In step S47), the cutting shaft moves to the grinding backward end (step S48).

  When the zero signal is received, if there is a misalignment in which the relative position X of the workpiece W deviates from the grinding reference position X0, as a part of the sharpness control of the grinding wheels 5 and 6, the grinding advance end is set at the grinding reference position at the next grinding. The back end correction means 25 corrects the position of the grinding back end of the grinding wheels 5 and 6, that is, the position of the grinding back end of the cutting shaft so as to coincide with X 0. Therefore, at the next grinding of the workpiece W, the grinding wheels 5 and 6 cut the workpiece W while absorbing the displacement of the relative position X of the workpiece W, and the positions R1 and R2 on both side surfaces of the workpiece W are set. It is possible to return to the grinding reference position X0.

  At the same time, if there is a left-right difference ΔR on both sides of the workpiece W, the post-correction unit 40 corrects and updates the grinding conditions that affect the sharpness of the grinding wheels 5 and 6 in preparation for the next grinding (step S49). Here, the grinding conditions that could not be changed during grinding, for example, the rotational speed of the grinding wheels 5 and 6 and / or the cutting speed of the grinding wheels 5 and 6 can be changed. The correction is performed based on the magnitude of the left / right difference ΔR and the correction direction.

  If the rotational speed of the grinding wheels 5 and 6 and / or the cutting speed of the grinding wheels 5 and 6 are corrected, the sharpness of the grinding wheels 5 and 6 can be adjusted. For example, if the number of revolutions of the grinding wheels 5 and 6 is decreased or the cutting speed is increased, the grinding load when the grinding wheels 5 and 6 grind the workpiece W increases, and the falling of the abrasive grains proceeds and new abrasive grains. Appear one after another, and even with the grinding wheels 5 and 6 having poor sharpness, the sharpness can be improved by the progress of the grinding wheel wear.

  Further, the grinding back ends of the grinding wheels 5 and 6 are corrected based on the displacement of the relative position X of the workpiece W, and the grinding conditions of both the grinding wheels 5 and 6 are corrected based on the positional difference ΔR between both side surfaces of the workpiece W. By doing so, compared with the case where the grinding conditions of only one of the grinding wheels 5 and 6 are corrected, the damage, warpage, etc. of the workpiece W after grinding are reduced, and the grinding accuracy of the workpiece W can be further improved. .

  Thereafter, the work W is taken out and the process ends (step S50).

  In this way, the unbalance of the sharpness caused by the variation in the grinding wheel wear amount of both grinding wheels 5 and 6 is quantified, and automatically based on this, the sharpness of both grinding wheels 5 and 6 becomes the same. Can be controlled. In addition, when grinding many workpiece | work W continuously, operation in the same procedure, control, etc. are performed repeatedly.

  FIG. 12 illustrates a second embodiment of the present invention. In the second embodiment, the relative position X of the workpiece W being ground and the grinding reference position X0 where the workpiece W should be properly held by the static pressure pads 1 and 2 are compared, and both grinding wheels are obtained by the difference between the two. The sharpness comparison means 26 that calculates the sharpness difference between the grinding wheels 5 and 6 and the grinding wheels 5 and 6 so that the sharpnesses of the grinding wheels 5 and 6 substantially match based on the sharpness difference between the grinding wheels 5 and 6. And grinding condition correction means 27 for correcting the grinding conditions of the grinding wheels 5 and 6 such as controlling the flow rate of the grinding water supplied between the workpiece W and the workpiece W.

  If there is a difference in the wear amount of the grinding wheels 5 and 6 due to long-term use, even if the cutting amounts of the grinding wheels 5 and 6 are the same, the grinding advance ends of the grinding wheels 5 and 6 are different. To do. On the other hand, in the grinding wheels 5 and 6 on the side where the grinding wheel wear amount is large, the sharpness is improved by the self-generated action and the machining allowance is large. Therefore, the workpiece W is worn by the grinding wheels 5 and 6 on the side where the grinding wheel wear amount is small. As a result, the relative position X of the workpiece W is shifted to the grinding wheel 5 or 6 side where the wear amount of the wheel is large and the sharpness is good.

  Thus, during grinding of the workpiece W, the relative position X of the workpiece W is obtained in real time, and the sharpness comparing means 26 compares the relative position X with the grinding reference position X0, and the sharpness of both grinding wheels 5 and 6 is determined by the difference between the two. The presence / absence of the positional deviation of the workpiece W due to the difference, the magnitude of the positional deviation, and the deviation direction are calculated.

  If there is a positional deviation of the relative position X of the workpiece W with respect to the grinding reference position X0, the grinding condition correction means 27 responds to the sharpness difference between the grinding wheels 5 and 6, that is, the magnitude of the positional deviation and the deviation direction. The flow rate of the grinding water supplied between the grinding wheels 5 and 6 and the workpiece W is controlled. As a result, the difference in sharpness between the grinding wheels 5 and 6 can be eliminated.

  Incidentally, when the flow rate of the grinding water of both grinding wheels 5 and 6 is controlled in accordance with the size of the relative displacement X and the displacement direction, the relationship shown in FIG. Just control.

  As mentioned above, although each embodiment of this invention was explained in full detail, this invention is not limited to these embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, although each embodiment illustrated about the horizontal type | mold double-sided surface grinder, it can implement similarly with a vertical-type double-headed surface grinder.

  The difference in sharpness between the grinding wheels 5 and 6 is calculated by calculating the positions R1 and R2 on both side surfaces of the workpiece W being ground, and comparing the positions R1 and R2 on both side surfaces, the difference in the amount of grinding wheel wear between both grinding wheels 5 and 6 And calculating a relative position X of the workpiece W during grinding, based on the difference between the grinding wheel wear amounts of the two grinding wheels 5 and 6, A method of comparing the relative position X and the grinding reference position X0 where the workpiece W should be properly held between the static pressure pads 1 and 2 and determining the sharpness difference between the grinding wheels 5 and 6 based on the difference between the two. However, any other method may be adopted as long as it measures the positions R1 and R2 on both sides of the workpiece W during grinding and determines the sharpness of both grinding wheels 5 and 6 based on the measured positions.

  Further, when the grinding condition is controlled by calculating the left / right difference ΔR between the positions R1, R2 on both side surfaces of the workpiece W, the sharpness difference between the grinding wheels 5 and 6 is determined based on the left / right difference ΔR. May be controlled to be substantially the same, or the difference in the grinding wheel wear amount of the grinding wheels 5 and 6 is determined based on the left-right difference ΔR, and the grinding wheel wear amount is controlled to be substantially the same. Also good.

  When measuring the gap D between the static pressure pads 1 and 2, for example, when the right static pressure pad 2 has only a vacuum pulling means and no jig 43, it is directly measured using a commercially available gap gauge. Also good. The left position D1 of the workpiece W is calculated by the following calculation formula D1 = D−D2 based on the pad position D2 of the right static pressure pad 2, the pad gap D grasped by the gap gauge, and the known thickness T of the workpiece W. It can also be obtained by -T. If the left position D1 of the workpiece W is known, the left pad position A1 is obtained based on the value, and the left pad position A1 is determined from the left pad position A1 and the measured values M1 and M2 of the left measuring head 9. It can also be obtained by the following arithmetic expression A1 = D1 + M1.

  Zeroing is best performed on the basis of the grinding reference position X0 when the workpiece W reaches the finishing dimension. However, in order to avoid scratches on the workpiece W, the workpiece W remains for the spark-out time set in the grinding conditions even after the zero signal is received from the sizing device 18 and both measuring heads 9 and 10 are retracted from the workpiece W. Since it is ground, zeroing at the finished dimensions is difficult. Therefore, it is desirable to perform the timing when the zero signal is received from the sizing device 18.

  During grinding, the workpiece W rotating while being held by the static pressure pads 1 and 2 is ground from both sides by the rotating grinding wheels 5 and 6, and both sides of the workpiece W are measured in real time by the measuring heads 9 and 10. Therefore, there is always a slight variation in the measured values M1 and M2 on both side surfaces. Accordingly, the relative position X of the workpiece W is preferably obtained by moving average processing of the measured values M1 and M2 of the measuring heads 9 and 10.

  In the embodiment, the measuring heads 9 and 10 of the sizing device 18 are used and the zero signal from the sizing device 18 is used. However, a dedicated measuring means including the measuring heads 9 and 10 is used. It is also possible to measure both side surfaces of the workpiece W and perform zeroing or the like in response to a signal when the workpiece W reaches a predetermined grinding accuracy instead of the zero signal from the sizing device 18.

  The measuring heads 9 and 10 can use a non-contact type such as a laser displacement type or a capacitance type in addition to a contact type that contacts both side surfaces of the workpiece W, and measure the positions of both sides of the workpiece W. If possible, the measurement method is not a problem.

  By using the position monitoring of the workpiece W by the measuring heads 9 and 10 and the position calculating means 22, it is possible to measure the automation of the grinding positioning operation after the replacement of the grinding wheels 5 and 6. As a result, it is possible to reduce the time for setup and the like, and it is possible to prevent the occurrence of misalignment due to human factors. That is, unless the alignment of the pair of static pressure pads 1 and 2 is adjusted, the grinding position is almost the same as before the grinding stones 5 and 6 are exchanged. What is necessary is just to match | combine with the position of the workpiece | work W within the reference value of the predetermined precision before replacement | exchange, Since the position has memorize | stored in the machine, automation can be achieved easily.

W Workpieces M1, M2 Measured value X Relative position X0 Grinding reference position M1r, M2r Reference value R1, R2 Side position Xabs Absolute position 1, 2 Hydrostatic pad 5,6 Grinding wheel 9,10 Measuring head 20 Grinding control device 22 Position Calculation means 23 Grinding reference position setting means 24 Position comparison means 25 Back end correction means 26 Sharpness comparison means 27 Grinding condition correction means

Claims (7)

When grinding both side surfaces of a thin plate-like workpiece held between a pair of static pressure pads with a pair of grinding wheels moving at substantially the same speed from a grinding back end to a grinding advance end at substantially the same speed,
Find the relative position between the static pressure pads of the workpiece being ground,
Compare the relative position of the workpiece during grinding with the grinding reference position where the workpiece between the hydrostatic pads should be properly held,
When there is a difference between the two, correct the grinding back end of the grinding wheel according to the difference between the two after grinding the workpiece so that the grinding advance end of both grinding wheels matches the grinding reference position at the next grinding. A thin plate-like workpiece grinding method characterized by the above. The method for grinding a thin plate workpiece according to claim 1, wherein the workpiece position when the grinding accuracy of the workpiece being ground is within the reference accuracy is a relative position. The position of the workpiece when the workpiece grinding accuracy is within the reference accuracy in the previous grinding is set as the grinding reference position.
The grinding reference position according to claim 1 or 2, wherein the grinding reference position is fixedly set. The workpiece position when the zero signal indicating the workpiece sizing is received from the sizing device in the prior grinding is set as the grinding reference position.
The method for grinding a thin plate workpiece according to any one of claims 1 to 3, wherein the position of the workpiece when a zero signal is received from the sizing device in the main grinding is a relative position. Comparing the relative position with the grinding reference position to calculate the deviation amount and the deviation direction of the relative position with respect to the grinding reference position,
The method for grinding a thin plate workpiece according to any one of claims 1 to 4, wherein the grinding backward end of the grinding wheel is corrected based on the deviation amount and the deviation direction. Measure the absolute position between the static pressure pads of the workpiece when the grinding accuracy of the workpiece is within the reference accuracy in the previous grinding,
The method for grinding a thin workpiece according to claim 3, wherein the grinding reference position is set when the absolute position is less than a threshold value determined by grinding accuracy. In a double-headed surface grinder that grinds both side surfaces of a thin plate-like workpiece held between a pair of hydrostatic pads by a pair of grinding wheels moving at substantially the same speed from a grinding backward end to a grinding forward end at substantially the same speed,
A pair of measuring heads that measure the positions of both sides of the workpiece being ground;
An arithmetic means for obtaining a relative position between the hydrostatic pads of the workpiece being ground from the measurement value of the measuring head when the grinding accuracy of the workpiece being grounded is within the reference accuracy;
Position comparison means for comparing the relative position of the workpiece being ground and the grinding reference position where the workpiece between the hydrostatic pads should be properly held to obtain a difference;
When there is a difference between the two, the grinding back end of the grinding wheel is corrected according to the difference between the two after grinding the workpiece so that the grinding forward end of both grinding wheels coincides with the grinding reference position at the next grinding. A double-head surface grinder characterized by comprising end correction means.

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