Patent Application
20170072529
The present invention relates to a surface grinding method for a workpiece and a surface grinder for surface-grinding a workpiece.
When grinding a workpiece of a hard brittle material such as a silicon wafer to be used for manufacturing a semiconductor device, in a surface grinder equipped with a cup-shaped grinding wheel, a load current of a grinding wheel spindle drive motor is monitored, while the grinding wheel at the distal end of a grinding wheel spindle is caused to cut in at a predetermined cut-in speed to perform in-feed grinding of the workpiece on a rotating table, and when the load current of the grinding wheel spindle drive motor exceeds a predetermined threshold due to loading of the grinding wheel, the grinding wheel is withdrawn to interrupt grinding, and the grinding wheel is then again caused to cut in into contact with the workpiece to thereby promote self-sharpening of the grinding wheel (Patent Document 1).
[Patent Document 1] Japanese Published Unexamined Patent Application No. 2006-35406
With such a conventional grinding method, the grinding wheel is caused to cut in at a predetermined cut-in speed, on the other hand, the grinding wheel is once withdrawn to interrupt grinding when loading occurs in the grinding wheel during grinding, and the grinding wheel is thereafter again caused to cut in to promote self-sharpening of the grinding wheel. Therefore, not only can the workpiece not be ground in a high-load state with high grinding efficiency of the grinding wheel, but as a result of the grinding cycle being prolonged, it has also been difficult to efficiently grind the workpiece in a short time.
Conventional grinding methods other than the grinding method of Patent Document 1 also include a grinding method of causing the grinding wheel to cut in at a constant cut-in speed with respect to the workpiece, and a grinding method (hereinafter, referred to as a common grinding method) of varying the feed speed sequentially in a speed reducing direction according to a cutting-in feed amount of the grinding wheel for a rough grinding feed, a semi-finish grinding feed, and a finish grinding feed while performing grinding.
However, with the former grinding method, the abrasion loss of the grinding wheel, the removal amount of the workpiece, and the cut-in amount of the grinding wheel may lose balance during grinding to lead to a sudden rise in grinding load or abrasion of only the grinding wheel in some cases, and it has been difficult to efficiently and stably grind the workpiece in a high-load state with excellent grinding efficiency of the grinding wheel.
Also with the latter grinding method, it has been impossible for the following reason to efficiently and stably grind the workpiece in a high-load state with excellent grinding efficiency of the grinding wheel. Particularly when grinding a workpiece of a hard brittle material which is high in hardness and brittle, because the feed speed of the grinding wheel is varied so as not to cause an overload state due to cut-in of the grinding wheel while performing the grinding, it is necessary to slow the cut-in speed of the grinding wheel to perform the grinding over a long time.
However, in the case of such a hard brittle material, self-sharpening (grains change) of the grinding wheel surface occurs several times during grinding, and the grinding load greatly changes up and down. This is because the grinding wheel is dull before self-sharpening, whereas once self-sharpening of the grinding wheel occurs, the grinding wheel has increased cutting edges to be suddenly improved in sharpness. As a result, the coefficient of friction between the grinding wheel and workpiece changes, and the grinding load greatly changes up and down, so that stably grinding efficiently in a short time at a high load with excellent grinding efficiency is impossible.
Also, it is often the case during self-sharpening that an axial distance between the grinding wheel spindle and rotating table is reduced because of sudden thermal displacement of the grinding wheel, workpiece, and/or machine due to an increase in frictional heat. This is equal to an increasing cut-in speed of the grinding wheel, which serves as a factor for an intensive rise in grinding load. Then, if the grinding load excessively rises, there is a possibility such that the machine may terminate machining based on detection of an abnormal grinding load, and the grinding wheel and/or workpiece may be damaged or the machine may be damaged in the worst case.
In view of such conventional problems, the present invention aims at providing a surface grinding method for a workpiece and a surface grinder capable of efficiently grinding a workpiece of a hard brittle material or others at a moderate high load and capable of preventing damage to the workpiece and/or grinding wheel and further to the machine due to a sudden rise etc., in grinding load, and moreover capable of reducing grinding wheel abrasion loss.
A surface grinding method for a workpiece according to an aspect of the present invention is, when surface-grinding a workpiece by a grinding wheel, monitoring a grinding load while reducing the grinding wheel in cut-in speed with a rise in the grinding load.
Also, a surface grinding method for a workpiece according to another aspect of the present invention is, when surface-grinding a workpiece by a grinding wheel, monitoring a grinding load while reducing the grinding wheel in cut-in speed when the grinding load rises and increasing the cut-in speed when the grinding load falls.
In addition, respective cut-in speeds with which the grinding wheel has a slower cut-in speed at a larger grinding load may have been set in a manner corresponding to a plurality of respective load thresholds of the grinding load, and after starting grinding at a predetermined speed, the grinding wheel may be decelerated or accelerated to a corresponding cut-in speed every time the grinding load rises or falls to a predetermined load threshold.
Also, a returning load threshold higher than a maximum load threshold at cut-in time of the grinding wheel may have been set, and the grinding wheel may be returned at a predetermined return speed while grinding when the grinding load exceeds the returning load threshold. A cut-in and return of the grinding wheel may be repeated before spark-out.
When the grinding load exceeds a load threshold for implementation of a speed limit, even if the grinding load thereafter falls to a load threshold of a predetermined cut-in speed, the grinding wheel may be caused to cut in at a limit cut-in speed slower than the predetermined cut-in speed, that is, the cut-in speed may not be made faster than the limit cut-in speed.
A surface grinder according to an aspect of the present invention is a surface grinder which in-feed grinds a workpiece by a grinding wheel, and includes a grinding load measuring means that measures a grinding load of the grinding wheel during grinding, a speed setting means in which a plurality of grinding wheel cut-in speeds are set corresponding to a plurality of load thresholds, and a speed control means that compares the grinding load during grinding with a load threshold while accelerating or decelerating the grinding wheel, on the basis of each load threshold, at a cut-in speed corresponding to each load threshold so that the grinding wheel is reduced or increased in cut-in speed with a rise or fall in the grinding load.
According to the present invention, there are advantages of being capable of efficiently grinding a workpiece of a hard brittle material or others at a moderate high load and capable of preventing damage to the workpiece and/or grinding wheel and further to the machine due to a sudden rise etc., in grinding load, and moreover being capable of reducing grinding wheel abrasion loss.
Hereinafter, embodiments of the present invention will be described in detail based on the drawings.
The sizing control means 10 measures the dimensions of a workpiece W during grinding by a size measuring means 12, and performs control so as to issue a spark-out instruction to the grinding wheel feed means 7 when it has reached a predetermined spark-out period in order to finish the workpiece W with a predetermined dimensional accuracy by spark-out.
In addition, the grinding wheel feed means 7, if a spark-out instruction is received, stops feeding the grinding wheel spindle 5 so that the grinding wheel 1 continues machining of the workpiece W at that position. When there is no sizing control means 10, a spark-out instruction may be issued when a predetermined cut-in amount is reached from the start of grinding of the workpiece W or when a predetermined time has elapsed.
The grinding wheel cut-in/return control means 11 is for monitoring a grinding load during grinding of the workpiece W while controlling the cut-in and return of the grinding wheel 1 so as to efficiently grind the workpiece W at a moderate high load of high grinding efficiency, and has a function of reducing the cut-in speed of the grinding wheel 1 with a rise in grinding load, a function of repeating a cut-in and return of the grinding wheel 1 when the grinding load has risen to near an upper limit, and a function of accelerating the grinding wheel 1 with a fall in grinding load.
The grinding wheel cut-in/return control means 11 specifically has a grinding load measuring means 13 that measures a grinding load of the grinding wheel 1 during grinding, a speed setting means 14 that sets a cut-in speed or return speed of the grinding wheel 1 for each load threshold, and a speed control means 15 that controls the grinding wheel feed means 7, through a comparison of an actual grinding load during grinding with a load threshold, at a cut-in speed or return speed set by the speed setting means 14 according to an increase or decrease in the grinding load.
The grinding load measuring means 13 is structured so as to measure a grinding load of the grinding wheel 1 during grinding according to a change in a current or power flowing in the grinding wheel drive means 6 or torque, etc. The speed setting means 14 has such a speed table as shown in
The high-speed cut-in is a cut-in when the grinding wheel 1 contacts the workpiece W and starts grinding, and its high-speed cut-in speed V0 is set to 0.5 (mm/min). The fast cut-in is set to a fast cut-in speed V1=0.3 (mm/min) for the load threshold L1, the intermediate cut-in is set to an intermediate cut-in speed V2=0.1 (mm/min) for the load threshold L2, and the slow cut-in is set to a slow cut-in speed V3=0.05 (mm/min) for the load threshold L3.
On the other hand, the slow return is set to a slow return speed V4=−0.05 (mm/min) for the load threshold L4, the intermediate return is set to an intermediate return speed V5=−0.1 (mm/min) for the load threshold L5, and the fast return is set to a fast return speed V6=−0.3 (mm/min) for the load threshold L6. The emergency return is set to a return speed V7 (full speed) for the load threshold L7.
In addition, because a return is in reverse direction to a cut-in, for the sake of description of the slow return speed V4 etc., the numerical value is affixed with a minus sign − to indicate heading in the reverse direction.
The respective load thresholds L1 to L7 are, as illustrated in
Accordingly, the high-speed cut-in, fast cut-in, intermediate cut-in, and slow cut-in decrease in speed in the cutting-in direction in stages to the cut-in speeds V1 to V3 as the grinding load increases in stages to the load thresholds L1 to L3. On the other hand, the slow return, intermediate return, fast return, and emergency return increase in speed in the returning direction in stages to the return speeds V4 to V7 as the grinding load increases in stages to the load thresholds L4 to L7. The return speeds V4 to V7 of the grinding wheel 1, at which the grinding wheel 1 moves in the direction reverse to the cutting-in direction, can therefore be said to decrease in stages from the slow return to the emergency return if the grinding wheel 1 is on the basis of the cutting-in direction.
In addition, when there is a standard speed table corresponding to a standard workpiece W, it also suffices to read out a numerical value from the standard speed table according to the difference in the material etc., of the workpiece W and correct the same while performing control.
As for the load threshold L3 for slow cut-in time and the load threshold L4 for slow return time, the load threshold L4 for slow return time is higher, and when a slow cut-in and a slow return are repeated multiple times before spark-out after exceeding the load threshold L3, the grinding wheel 1 is switched between the slow cut-in and slow return on the basis of the load threshold L4 in such a manner as to, for example, perform a slow cut-in of the grinding wheel 1 when the grinding load is equal to the load threshold L3 or more and less than the load threshold L4 and perform a slow return of the grinding wheel 1 when the grinding load is equal to the load threshold L4 or more.
Next, a grinding method for a workpiece W will be described with reference to the flowchart in
Immediately after the grinding operation is started, because it is not yet in a spark-out period (S4), it is determined whether or not the grinding load is less than the load threshold L1 for a fast cut-in (S5), the feed speed of the grinding wheel spindle 5 is reduced from the high-speed feed speed to the high-speed cut-in speed V0, and the grinding wheel 1 begins to grind the workpiece W at that high-speed cut-in speed V0 (S6).
Feeding the grinding wheel spindle 5 at a high-speed feed speed faster than the high-speed cut-in speed V0 until the grinding wheel 1 contacts the workpiece W and reducing the feed speed to the high-speed cut-in speed V0 immediately before the grinding wheel 1 contacts the workpiece W allows reducing air cut time to efficiently shift to grinding of the workpiece W.
When the grinding wheel 1 contacts the workpiece W and starts grinding, a grinding load on the grinding wheel spindle 5 rises, but the grinding wheel 1 is caused to cut in forward at the high-speed cut-in speed V0 as long as the grinding load is less than the load threshold L1 (S6). Then, when the grinding load rises due to the high-speed cut-in at the high-speed cut-in speed V0 to become equal to the load threshold L1 or more and less than the load threshold L2 (S5, S7), the cut-in speed of the grinding wheel 1 is reduced from the high-speed cut-in speed V0 to the fast cut-in speed V1 (S8), and the grinding wheel 1 is caused to cut in forward at that fast cut-in speed V1 while continuing the grinding of the workpiece W.
When the grinding load rises due to the fast cut-in at the fast cut-in speed V1 to become equal to the load threshold L2 or more and less than the load threshold L3 (S7, S9), the cut-in speed of the grinding wheel 1 is reduced from the fast cut-in speed V1 to the intermediate cut-in speed V2 for intermediate cut-in (S10), and the grinding wheel 1 is caused to cut in at that intermediate cut-in speed V2.
Also, when the grinding load rises due to the intermediate cut-in at the cut-in speed V2 to become equal to the load threshold L3 or more and less than the load threshold L4 (S9, S11), the cut-in speed of the grinding wheel 1 is reduced from the intermediate cut-in speed V2 to the slow cut-in speed V3 for slow cut-in (S12), and the grinding wheel 1 is caused to cut in at that slow cut-in speed V3 while continuing the grinding of the workpiece W.
As above, grinding is started at the fast high-speed cut-in speed V0, and while the grinding load then rises from the load threshold L1 through the load threshold L2 up to the load threshold L3 or more, the grinding wheel 1 is decelerated in stages to the cut-in speeds V1 to V3 while being caused to cut in forward.
In addition, if the grinding load falls in a manner such as to increase the cut-in speed of the grinding wheel 1 from the slow cut-in speed V3 to the intermediate cut-in speed V2 (S10) when the grinding load becomes less than the load threshold L3 during a slow cut-in of the grinding wheel 1 (S9), the cut-in speed of the grinding wheel 1 is increased with the fall in grinding load.
When the grinding load rises during grinding at the slow cut-in speed V3 to become equal to the load threshold L4 or more and less than the load threshold L5 (S11, S13), the grinding wheel 1 is returned by a slow return at the slow return speed V4 switched from the slow cut-in at the slow cut-in speed V3 while continuing the grinding of the workpiece W (S14). Also, when the grinding load becomes less than the load threshold L4 during grinding by the slow return (S1), the grinding wheel 1 is caused to cut in slowly by a slow cut-in at the slow cut-in speed V3 switched from the slow return at the slow return speed V4 (S12).
Accordingly, when the grinding of the workpiece W proceeds until the grinding load of the grinding wheel 1 reaches a high load region near the load threshold L4, the grinding wheel 1 thereafter performs a slow cut-in and a slow return one time or multiple times by repetition at loads higher or lower than the load threshold L3, L4 while continuing later-stage grinding of the workpiece W.
The sizing control means 10 is also reading in the dimensions of the workpiece W in the meantime, and when it reaches a spark-out period where the dimensions are close to those of a predetermined finishing accuracy (S4), the grinding wheel feed means 7 stops moving the grinding wheel 1 based on a spark-out instruction from the sizing control means 10, and spark-out is performed in which the grinding wheel 1 grinds the workpiece W at the stop position (S21). Then, the grinding is terminated when the workpiece W has reached the finish dimensions due to the spark-out (S22).
In addition, when the grinding load becomes equal to the load threshold L5 or more and less than the load threshold L6 during grinding by the slow return (S13, S15), the grinding wheel 1 is returned at the intermediate return speed V5 while continuing the grinding (S16), and further when the grinding load becomes equal to the load threshold L6 or more and less than the load threshold L7 during that intermediate return (S15, S17), the grinding wheel 1 is returned at the fast return speed V6 while continuing the grinding (S18).
Moreover, when the grinding load becomes equal to the load threshold L7 or more (S17), an emergency return is performed at the emergency return speed V7 (full speed) (S19), and the grinding is suspended (S20). Then, after suspending the grinding, appropriate measures are implemented such as performing dressing or the like of the grinding wheel 1 to regain the sharpness of the grinding wheel 1.
As above, a high-speed cut-in of the grinding wheel 1 is started at the high-speed cut-in speed V0, followed by monitoring variation in the grinding load of the grinding wheel 1, while reducing the cut-in speed of the grinding wheel 1, with a sequential rise in the grinding load from the load threshold L1 through the load threshold L2 to the load threshold L3, sequentially from that of a high-speed cut-in to that of a fast cut-in, and from that of a fast cut-in to that of an intermediate cut-in, and from that of an intermediate cut-in to that of a slow cut in.
Accordingly, employing such a grinding method enables grinding the workpiece W by the grinding wheel 1 so that the cut-in speed of the grinding wheel 1 is almost coincident with a speed at which the workpiece W is gradually ground by the grinding wheel 1, which allows efficiently grinding the workpiece W with a moderate high load of high grinding efficiency applied to the grinding wheel 1.
Particularly when the grinding wheel 1 is caused to cut in forward at high speed, the speed at which the workpiece W is gradually ground by the grinding wheel 1 and the cut-in speed of the grinding wheel 1 become no longer coincident with each other as the grinding proceeds, which causes grinding burrs on the workpiece W side to result in an abnormal rise in the grinding load of the grinding wheel 1. As a result, continuing the grinding remaining in the high-speed cutting-in state results in an excessively large load to be applied to the workpiece W to cause a problem such as splitting of the workpiece W. However, the grinding load is monitored, while the cut-in speed of the grinding wheel 1 is reduced with an increase in grinding load, and therefore, such a case as to the application of an excessively large load on the workpiece W can be prevented.
Also, in the later stage of the grinding of the workpiece W, because the grinding wheel 1 is switched to a slow return if the grinding load rises to L4 during grinding by a slow cut-in after the grinding load rises to the load threshold L3 or more, the workpiece W is ground in a high-load state with the slow cut-in and the slow return being repeated. Therefore, there is no such case that the grinding load of the grinding wheel 1 continues rising to apply an excessively large load on the workpiece W, and the grinding can be continued at a moderate high load of high grinding efficiency.
With conventional common grinding, because the grinding is performed with the cut-in speed of the grinding wheel 1 controlled depending on the cutting-in feed amount of the grinding wheel 1 for a rough grinding feed, a semi-finish grinding feed, and a finish grinding feed so as to prevent overloading, grinding at a slow cutting-in speed as shown by the grinding load curve A1 in
On the other hand, with the present invention, as shown by the grinding load curve A in
Because the self-sharpening effect of abrasive grains can therefore be promoted by a rise in the grinding load of the grinding wheel 1, it is possible to grind the workpiece W in a short time with high grinding efficiency, and grinding can be efficiently performed in a grinding cycle shorter than that of conventional common grinding. As a result, the grinding time with the present invention can be reduced to on the order of approximately ⅔ compared with that in the case of conventional common grinding, which proves that efficient grinding is possible. Also, with the present invention, because grinding is efficiently performed at a high load of high grinding efficiency, a rise in grinding temperature can be prevented as compared with the case of common grinding in which grinding is performed at a low grinding load.
The speed limit implementation means 14A has a function of implementing a speed limit, when the grinding load of the grinding wheel 1 exceeds a load threshold LA for speed limit implementation, to limit the cut-in speed of the grinding wheel 1 to a limit cut-in speed Vα (=0.03 mm/min) slower than the slow cut-in speed V3 (=0.05 mm/min) even if the grinding load thereafter falls to less than the load threshold L3 for a slow cut-in.
The speed table is configured as shown in
In in-feed grinding of the workpiece W, as shown in FIG. 8, it is determined whether or not the grinding load is equal to the load threshold LX for the time of grinding suspension or more (S23), and the grinding is suspended (S24) if it is equal to the load threshold LX or more. On the other hand, when the grinding load is less than the load threshold LX, it is checked whether or not the grinding load has reached so far the load threshold LA for the time of speed limit implementation or more (S25), and if so even once, even when the grinding load is less than the load threshold L4 (S26), the grinding wheel 1 is limited to the limit cut-in speed Vα (=0.03 mm/min) (S27). If the grinding load has never reached the load threshold LA or more, the grinding load is compared with the load threshold L1 (S28), if less than the load threshold L1, the cut-in speed V0 for a high-speed cut-in is employed (S29). On the other hand, when the grinding load is equal to the load threshold L1 or more, if less than the load threshold L2 compared with the load threshold L2 (S30), the cut-in speed V1 for a fast cut-in is employed (S31).
Likewise, when the grinding load is equal to the load threshold L2 or more, if less than the load threshold L3 compared with the load threshold L3 (S32), the cut-in speed V2 for an intermediate cut-in is employed (S33). On the other hand, when the grinding load is equal to the load threshold L3 or more, if less than the load threshold L4 compared with the load threshold L4 (S34), the slow cut-in speed V3 for a slow cut-in is employed (S35). When the grinding load during grinding by a slow cut-in has reached the load threshold L4 or more, the grinding wheel 1 is returned at the slow return speed V4 (S36), in order to achieve a fall in grinding load by the slow return of the grinding wheel 1.
Also during the grinding by a slow return, the grinding load of the grinding wheel 1 is being compared with the load threshold LA for the time of speed limit implementation (S37), and the process returns to step S2 if it is less than the load threshold LA. However, if the grinding load does not fall during grinding by a slow return and the grinding load temporarily rises for some cause to the load threshold LA for the time of speed limit implementation or more (S37), it is memorized that the grinding load has exceeded the load threshold LA (S38), and the speed limit implementing function of the speed limit implementation means 14A then works.
If the cause for the temporal rise in grinding load is thereafter eliminated, the grinding load suddenly falls due to the slow return at the slow return speed V4 of the grinding wheel 1. However, because the grinding load has once exceeded the load threshold LX (S25), even if the grinding load of the grinding wheel 1 becomes less than the load threshold L4 for slow cut-in time (S26), the speed limit implementing function of the speed limit implementation means 14A works to limit a subsequent cut-in of the grinding wheel 1 to the slowest, limit cut-in speed Vα (=0.03 mm/min) (S27) without employing the original slow cut-in speed V3 (=0.05 mm/min).
Accordingly, there is no such case that the grinding wheel 1 and the workpiece W repeat contact and separation. This is because, without the speed limit implementing function, when the grinding load falls to less than the load threshold L3 during grinding of the workpiece W by a slow return (S34), the grinding wheel 1 is caused to cut in at the slow cut-in speed V3 by a slow cut-in switched from the slow return. Therefore, if the cut-in speed of the grinding wheel 1 is controlled according to a rise and fall in grinding load, the grinding wheel 1 intensively move back and forth at a fast cutting-in speed and a fast returning speed to cause repeated contact and separation between the grinding wheel 1 and the workpiece W, so that the grinding of the workpiece W may no longer proceed.
However, even when the grinding load falls to less than the load threshold L3 due to the slow return of the grinding wheel 1, the grinding wheel 1 is caused to cut in slowly at a slower speed of the limit cut-in speed Vα (=0.03 mm/min) without immediately causing cut-in at a faster speed of the cut-in speed V3 (=0.05 mm/min), so that a sudden rise in the grinding load of the grinding wheel 1 can be prevented by switching from the slow return to the slow cut-in, and there is no such case that the grinding wheel 1 intensively repeats a return and a cut-in. Therefore, like the grinding load curve shown in
In addition, in the present embodiment, control is performed so as not to cause the grinding wheel 1 cut in at a speed faster than the limit cut-in speed Vα even when the grinding load falls after exceeding the load threshold LA for the time of speed limit implementation, but in the case of returning the grinding wheel 1 as well, a limit return speed V1 may be set so as not to cause a return at a return speed faster than the limit return speed Vβ, after the grinding load exceeds a certain load threshold LB, even if there is such a case that the grinding load thereafter falls to nearly above the load threshold L4.
Examples of the tables stored in the speed setting means 14 include a first speed table T1 shown in
The joint table is a single speed table for which a front-behind relationship of the first speed table T1 and the second speed table T2 is selected and a speed table changing load when changing from that one of the speed table T1 or the speed table T2 to another of the second table T2 or the speed table T1 is set to a load threshold appropriately and which is configured so as to join both speed tables T1 and T2 in a manner changed in the front-behind relationship at the speed table changing load, for switching from the one of the speed table T1 or the speed table T2 to another of the second table T2 or the speed table T1 at the speed table changing load.
For example, when selection is performed to have the first speed table T1 in front and have the second speed table T2 behind and the load threshold L3 is set as the speed table changing load, a single speed table for which a first half of the first speed table T1 up to the load threshold L3 and a second half of the second speed table T2 from the load threshold L3 onward are joined can be configured.
Accordingly, in in-feed grinding, the grinding wheel cut-in/return control means 11 monitors a change in grinding load while respectively controlling the cut-in speeds of the grinding wheel 1 according to the joint table by its speed control means 15. For example, control is performed according to the first speed table T1 in a first half of the grinding, and a slow cut-in of the grinding wheel 1 is performed at a slow cut-in speed V3 (=0.05 mm/min) of the first speed table T1 when the grinding load is less than the load threshold L3. Then, when the grinding load becomes equal to the load threshold L3 or more, through a change from the first speed table T1 to the second speed table T2, a slow return of the grinding wheel 1 is performed at a slow return speed V3 (=−0.05 mm/min) according to the second speed table T2. In addition, other aspects of the configuration, control, etc., are the same as those of each embodiment.
Doing this allows configuration of a joint table by selectively combining the first speed table T1 with the second speed table T2 in part, and grinding is possible under conditions optimal for the material of the workpiece W and others despite the basis of the small number of speed tables T1 and T2.
In addition, there may be three types or more of speed tables, and may be a plurality of types of speed table changing loads. Also, besides changing tables depending on the speed table changing load, a plurality of speed tables may be changed over on the basis of a cut-in time, a cut-in amount, a removal amount read from a sizing device or the like.
In the case of the speed table in
In actual in-feed grinding, which of the rising or falling aspects grinding at that point in time is in may be judged by having determined a determination time on the order of a past few seconds-period and obtaining a moving average or the like of the grinding load in that determination time.
In the grinding wheel cut-in/return control means 11 thus configured, if the acceleration/deceleration time T is preset by the time setting means 17, a sudden change in speed can be prevented in either case of the time of change in cut-in speed and the time of switching between cut-in and return, so that there is no such a problem that the grinding load temporarily falls, which allows efficiently grinding the workpiece W at a high grinding load.
For example, in the case of a decrease in speed from a high-speed cut-in at cut-in speed V0 to a fast cut-in at cut-in speed V1, because the speed is gradually reduced from the cut-in speed V0 to the cut-in speed V1 in the acceleration/deceleration time T as shown by the solid line in
Also in the case of switching from a slow cut-in at cut-in speed V3 to a slow return at return speed V4 as well, because of gradual switching from the cut-in speed V3 to the return speed V4 in the acceleration/deceleration time T as shown by the solid line in
In addition, the acceleration/deceleration time T can also be appropriately set according to the material etc., of the workpiece W. Also, the speed control means 15 may increase or reduce the speed gradually or in stages in accordance with predetermined acceleration/deceleration characteristics at the time of change in cut-in speed or at the time of switching between cut-in and return, besides enabling setting the acceleration/deceleration time T variable.
Although embodiments of the present invention have been described in detail hereinabove, the present invention should not be limited thereto and various modifications can be made. For example, load thresholds of the grinding load are desirably large in number. Accordingly, it is also possible to increase the number of load thresholds to a countless number, and increasing the number of load thresholds to a countless number enables a stepless speed change as well which reduces the cut-in speed of the grinding wheel 1 with an increase in grinding load in a stepless manner.
Also, in the embodiments, the workpiece W of a hard brittle material is exemplified, however, the present invention can likewise be carried out for the whole of surface grinding of workpieces W of various materials, without limitation to hard brittle materials.
Although rotational load torque of the grinding wheel spindle 5 is exemplified as the grinding load, the grinding load may be judged based on a change in the current or power of the grinding wheel drive means 6 or a change in the load applied to the grinding wheel drive means 6, or the grinding load may be judged based on a change in the torque, current, power, or load of the workpiece drive means 4. Also, in the case of the surface grinder 2 without a workpiece drive mechanism, the grinding load may be judged from a load on the workpiece W. Further, a judgment may also be made in combination of two or more related factors related to a change in grinding load, such as combination of a change in the current, power, or load of the grinding wheel drive means 6 and a change in the current, power, or load of the workpiece drive means 4.
In the first and second embodiments, a detailed description has been given of the case of a rise in grinding load during cut-in, however, control may of course be performed so as to increase the cut-in speed if the grinding load falls under a predetermined load threshold during cut-in. Also in that case, the cut-in speed may be increased over a predetermined time.
When the grinding load increases or reduces the cut-in speed on the basis of a predetermined load threshold or performs switching between cut-in and return, it suffices as long as a cut-in, return, or the like of the grinding wheel 1 is possible on the basis of the predetermined load threshold, and judging is also possible by either criterion of being less than the load threshold or equal to the load threshold or more.
The high-speed cut-in, fast cut-in, intermediate cut-in, slow cut-in, slow return, intermediate return, fast return, etc., are merely exemplified, and the cut-in and return may be further finely divided, or may be roughly divided into a smaller number. The values of the respective load thresholds, cut-in speeds, and return speeds are also merely exemplified, and are not limited thereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-183134 | Sep 2015 | JP | national |
