Method for controlling grinding process

In a grinding machine, either the revolutional speed of the workpiece or of the grinding wheel is controlled and further the infeed speed of the wheel to the workpiece is controlled so that the optimum grinding condition, having a suitable ratio of the workpiece surface speed to the grinding wheel surface speed and a suitable ratio of the infeed speed to the workpiece revolutional speed, is obtained. The former ratio is maintained despite the wheel diameter decrease caused by wheel dressings.

BACKGROUND OF THE INVENTION 
This invention relates to a controlling method for a grinding process. 
In a grinding process, the speed ratio K.sub.v (workpiece surface 
speed/grinding wheel surface speed) and infeed amount per one workpiece 
revolution .DELTA. (infeed speed per minute/workpiece revolution per 
minute) have influence on grinding accuracy and efficiency. For obtaining 
both high grinding accuracy and high grinding efficiency, it is 
advantageous that rough grinding is performed under a condition in which 
the infeed amount .DELTA. is higher so that the ground surface of the 
workpiece is rather rough but good metal removal with high grinding 
ability is maintained so as to improve roundness and cylindricity of the 
workpiece, and that fine grinding is performed in a condition in which the 
infeed amount .DELTA. is lower so that grinding efficiency is rather poor 
but surface roughness of the workpiece is improved. 
Further, revolution speeds of the workpiece and the grinding wheel, and 
infeed speed should be controlled to keep optimum K.sub.v and .DELTA.. 
In conventional grinding methods, revolution speeds of the workpiece and 
the grinding wheel, and infeed speed in rough or fine grinding step are 
respectively kept constant. Accordingly, the speed ratio K.sub.v is 
approximately constant and is not always suitable for rough grinding or 
fine grinding. Good surface roughness of the workpiece cannot be attained, 
in the prior art, without long time spark-out after fine grinding, in the 
spark-out metal removal rate diminishing as time passes, because the 
revolution speed of the workpiece in fine grinding is the same as that in 
rough grinding and is not suitable for improving surface roughness of the 
workpiece. Moreover, this surface roughness improving method with longer 
spark-out cannot effect constant quality on the workpiece surface as the 
grinding ability of the wheel or other factors sometimes changes the 
surface roughness. 
The grinding wheel becomes smaller in the diameter after several dressings, 
shifting K.sub.v and .DELTA. to unsuitable values during rough and fine 
grinding which deteriorates grinding accuracy and efficiency. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a 
controlling method for a grinding process in which high grinding accuracy 
and high grinding efficiency are always kept over long working operation. 
It is another object of the invention to provide a controlling method for a 
grinding process in which speed ratio K.sub.v of the workpiece surface 
speed to the grinding wheel surface speed and infeed amount per workpiece 
revolution .DELTA. are so selected as to be suitable for roundness and 
cylindricity improvement in a rough grinding step and as to be suitable 
for surface roughness improvement in a fine grinding step respectively. 
It is still another object of the invention to provide a controlling method 
for a grinding process in which the effect of the grinding wheel diameter 
decreasing due to its dressings is cancelled with controlling workpiece 
revolution speed, grinding wheel revolution speed and/or infeed speed. 
With the method of the invention, larger K.sub.v and .DELTA. are applied to 
the rough grinding step bringing higher grinding condition for obtaining a 
high rate of metal removal and geometrical accuracy such as roundness, 
cylindricity and size, while smaller ones are applied to the fine or 
finish grinding step bringing polishing condition for obtaining finer 
surface roughness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiments of the Invention will now be described referring 
to the attached drawings, in which FIG. 1 shows an infeed-time diagram of 
the grinding process using a controlling method of the invention. 
FIG. 2 is a block diagram showing an embodiment of the invention, in which 
numeral 1 designates a servo-motor for infeeding a workpiece toward a 
grinding wheel, servomotor 1 being controlled by a driving circuit 2, and 
numeral 3 designates a motor for driving the workpiece to rotate, motor 3 
being controlled by a driving circuit 4. Driving circuits 2 and 4 receive 
set-up signals respectively from a rough infeed amount setting circuit 6 
and a fine infeed amount setting circuit 7 through a switching circuit 5. 
Rough infeed amount setting circuit 6 sets a speed V.sub.F.sbsb.1 for 
servo-motor 1 and a speed N.sub.W.sbsb.1 for motor 3, in this working 
condition surface roughness of the workpiece being rather poor but metal 
removal rate and geometric improvement of the workpiece being superior. 
Fine infeed amount setting circuit 7 sets a speed V.sub.F.sbsb.2 for 
servo-motor 1 and a speed N.sub.W.sbsb.2 for motor 3, in this working 
condition grinding efficiency being rather poor but superior surface 
roughness being attained. Numeral 8 designates an infeed table position 
determining device. The output signal of infeed table position determining 
device 8 is fed to Schmidt trigger circuits 9. 
One of Schmidt trigger circuits 9 generates an output signal P.sub.1 when 
the infeed table position becomes equal to a predetermined quick infeed 
end point. A second of the circuits 9 generates an output signal P.sub.2 
when the infeed table position becomes equal to a predetermined rough 
infeed end point, a third of the circuits 9 generating an output signal 
P.sub.3 when the infeed table position becomes equal to a predetermined 
fine infeed end point. The outputs P.sub.1, P.sub.2 and P.sub.3 are 
amplified by amplifiers 10 and fed to switching circuit 5. 
The output signal P.sub.1 of amplifier 10 is fed to the setting terminal S 
of an R-S flip-flop circuit 51 of setting-preferential type (the following 
flip-flop circuits are the same types), while the output signal P.sub.2 is 
fed to resetting terminals R of flip-flop circuits 51 and 52 and to 
setting terminals S of flip-flop circuit 53 and 54, and the output signal 
P.sub.3 is fed to the resetting terminal R of flip-flop circuit 53 and to 
the setting terminal S of flip-flop circuit 54. Output terminals Q of 
flip-flop circuits 51, 52, 53 and 54 are respectively connected to the 
control terminals of well-known electronic switches T.sub.1, T.sub.2, 
T.sub.3, and T.sub.4 e.g. FET.sub.s. Electronic switch T.sub.1 is 
connected between the infeed speed value V.sub.F.sbsb.1 output terminal 
(for servomotor 1) of rough infeed amount setting circuit 6 and a control 
terminal of driving circuit 2 to thereby on-off control the input of 
infeed speed V.sub.F.sbsb.1 to driving circuit 2. Electronic switch 
T.sub.2 is connected between the workpiece revolutional speed value 
N.sub.W.sbsb.1 output terminal of rough infeed amount setting circuit 6 
and a control terminal of driving circuit 4 for motor 3, electronic switch 
T.sub.3 is connected between the infeed speed value V.sub.F.sbsb.2 output 
terminal of fine infeed amount setting circuit 7 and a control terminal of 
driving circuit 2 for servo-motor 1, and further, electronic switch 
T.sub.4 is connected between the workpiece revolutional speed value 
N.sub.W.sbsb.2 output terminal of fine infeed amount setting circuit 7 and 
a control terminal of driving circuit 4. Fourth flip-flop circuit 54 is to 
receive the output of a timer 11, which gives spark-out time, at the 
resetting terminal R thereof. Timer 11 is energized to start its operation 
for generating the output in response to signal P.sub.3. Setting terminal 
of second flip-flop circuit 52 is connected to the cycle-start output 
terminal of a grinding-cycle control circuit which is not shown in the 
drawings. 
In operation of the above described embodiment, after a workpiece is 
mounted on the work spindle and the grinding machine is started, at first, 
a cycle start signal is generated at the grinding cycle control circuit 
and sets flip-flop circuit 52, making output Q of the flip-flop 52 1-level 
whereby electronic switch T.sub.2 is switched on. Accordingly, workpiece 
revolution speed value NW.sub.1 of rough infeed amount setting circuit 6 
is fed to driving circuit 4 to drive motor 3 at revolutional speed 
NW.sub.1. A position signal P.sub.1 is fed out from Schmidt trigger 
circuits 9 to switching circuit 5 when a rapid infeed step is finished and 
a rough grinding infeed step is now starting as shown in FIG. 1. Signal 
P.sub.1 sets flip-flop 51 to level 1 at the terminal Q, and thereby 
electronic switch T.sub.1 is switched on to connect rough infeed amount 
setting circuit 6 to driving circuit 2. Accordingly, rough grinding step 
is carried with a heavier infeed per workpiece revolution, servo-motor 
driving the infeed table with the rough grinding infeed speed 
V.sub.F.sbsb.1. 
Reaching to point P.sub.2 in FIG. 2 after rough grinding in the above 
working condition, Schmidt trigger circuits 9 generates and feeds output 
signal P.sub.2 to switching circuit 5. Signal P.sub.2 resets flip-flops 51 
and 52 to level 0 at their output terminals Q, and thereby electronic 
switches T.sub.1 and T.sub.2 are switched off. At the same time, signal 
P.sub.2 sets flip-flops 53 and 54 to level 1 at their output terminals Q, 
and thereby electronic switches T.sub.3 and T.sub.4 are switched on to 
connect fine infeed amount setting circuit 7 to driving circuit 2 and 4 
respectively. Accordingly, driving circuit 2 drives servo-motor 1 at a 
predetermined fine grinding infeed speed T.sub.F.sbsb.2 and driving 
circuit 4 drives motor 3 at a predetermined fine grinding revolutional 
speed N.sub.W.sbsb.2, whereby the fine grinding on the workpiece proceeds. 
When the workpiece diameter reaches the finished size, a position signal 
P.sub.3 is fed out from Schmidt trigger circuit 9 to switching circuit 5, 
and flip-flop 53 is reset to level 0 at its output terminal Q, electronic 
switch T.sub.3 being switched off. The infeed is accordingly stopped and 
the spark-out step begins. At this time, timer 11 starts to operate to 
reset flip-flop 54 after the spark-out step. This resetting causes 
switching-off of electronic switch T.sub.4. On the other hand, on account 
of the time-up signal of timer 11, i.e. a grinding finish signal, the 
infeed table, which is not shown in the drawings, is made free from its 
driving mechanism including servo-motor 1 and is returned back by spring 
force. 
FIG. 3 shows another embodiment according to the invention, in which 
reference marks P.sub.1, P.sub.2, V.sub.F and N.sub.W are used as the same 
meanings in FIG. 2. 
This embodiment of FIG. 3 eliminates the bad influence of grinding wheel 
surface speed decreasing due to dressing operations, which shifts the 
ratio K.sub.v. 
Numeral 101 in FIG. 3 designates a cylindrical or internal grinding machine 
controlled in a predetermined process by a control circuit 102. 
Numeral 103 designates an operation circuit which computes workpiece 
revolution speed N.sub.W, grinding wheel revolution speed N.sub.S and 
infeed speed V.sub.F applicable to keeping the ratio K.sub.V and the 
infeed rate .DELTA. optimum for rough or fine grinding. Presetting circuit 
104 is provided and has optimum values of the ratio K.sub.V.sbsb.1 and the 
infeed rate .DELTA..sub.1 for rough grinding, and of the ratio 
K.sub.V.sbsb.1 and the infeed rate .DELTA..sub.2 for fine grinding, the 
grinding wheel diameter D.sub.S, the initial value of the wheel diameter 
D.sub.O, the workpiece diameter to be worked D.sub.W, and a dressing 
infeed depth C preset for supplying them to operation circuit 103. 
A Schmidt trigger circuit 122 is triggered to generate signal P.sub.1 when 
applied a signal corresponding to the rough grinding starting position 
from position determining device 121, while the other Schmidt trigger 
circuit 123 generates signal P.sub.2 when the infeed table is located to 
change to the fine infeed from the rough infeed. Signal P.sub.1 is fed to 
the setting terminal S of flip-flop circuit 131, and signal P.sub.2 is fed 
to the resetting terminal R of flip-flop circuits 131 and 132 and further 
to the setting terminals S of flip-flop circuits 133 and 134, similarly to 
the former embodiment. 
The setting terminal of flip-flop 132 is connected to the output terminal 
C.sub.O of grinding cycle starting signal on control circuit 102, and the 
resetting terminal R of flip-flop 133 is connected to the size-up or 
spark-out signal terminal S.sub.1 on control circuit 102, and further, the 
resetting terminal R of flip-flop 134 is connected to the finish size 
signal terminal F. 
The output Q of flip-flop 131 controls an electronic switch T.sub.31 to 
switch on-and-off the conductive lines from the output terminal 
V.sub.F.sbsb.1 of operation circuit for rough infeed to control circuit 
102, the output Q of flip-flop 132 controls an electronic switch T.sub.32 
to switch on-and-off the lines from the output terminal N.sub.S.sbsb.1 for 
grinding wheel revolution and the output terminal N.sub.W.sbsb.1 for 
workpiece revolution of rough grinding to the corresponding terminals of 
control circuit 102. The output terminal Q of flip-flop 133 controls an 
electronic switch T.sub.33 to switch on-and-off the lines from the output 
terminal V.sub.F.sbsb.2 of the operation circuit 103 for fine infeed to 
the corresponding terminal of control circuit 102, and further, the output 
Q of flip-flop 134 controls an electronic switching circuit T.sub.34 to 
switch on-and-off the lines from the output terminal N.sub.S.sbsb.2 for 
grinding wheel revolution and the output terminal N.sub.W.sbsb.2 for 
workpiece revolution of fine grinding to the corresponding terminals of 
control circuit 102. 
Operation circuit 103 is to receive dressing number signal n from a 
dressing number detecting circuit 105 which includes a skip counter 
operated by every predetermined number of workpiece grindings or a 
detector to detect over power consumption of the wheel spindle motor 
caused by excessive grinding force due to the loading of the wheel. 
With the signals of dressing number n generated at dressing number 
detecting circuit 105 and optimum ratios K.sub.V.sbsb.1 and 
K.sub.V.sbsb.2, optimum infeed rates .DELTA..sub.1 and .DELTA..sub.2, 
initial wheel diameter D.sub.O, workpiece diameter D.sub.w, wheel 
revolution speeds N.sub.W, and dressing amount C preset at presetting 
circuit 104, the output signals of most suitable workpiece revolution 
speeds N.sub.W.sbsb.1 and N.sub.W.sbsb.2, wheel revolution speeds 
N.sub.S.sbsb.1 and N.sub.S.sbsb.2 and infeed speeds V.sub.F.sbsb.1 and 
V.sub.F.sbsb.2 are computed out in operation circuit 103. These output 
signals are selectively fed to the control circuit in response to the 
select signals P.sub.1, P.sub.2, C.sub.O and F which have been described 
above, for controlling grinding machine 101. 
More particularly describing, the diameter D.sub.S of the grinding wheel on 
working is given as, 
EQU D.sub.S = D.sub.O - nC 
and, infeed speeds V.sub.F.sbsb.i for rough and fine grinding are given as, 
EQU V.sub.F.sbsb.i = N.sub.W.sbsb.i .DELTA..sub.i / 60 . . . (i = 1 or 2) 
and further, the operation of formula 
EQU N.sub.W.sbsb.i = N.sub.S.sbsb.i K.sub.V.sbsb.i D.sub.S / D.sub.W 
is carried for getting outputs V.sub.F.sbsb.i and N.sub.W.sbsb.i, outputs 
N.sub.S.sbsb.i being directly set at the corresponding terminals. 
Operation of this embodiment is similar to the former in FIG. 2, cycle 
start signal C.sub.O serving to set the revolution speeds of the workpiece 
and the grinding wheel respectively to N.sub.W.sbsb.1 and N.sub.S.sbsb.1, 
infeed position signal P.sub.1 serving to set the infeed speed of the 
infeed table to V.sub.F.sbsb.1, and infeed position signal P.sub.2 serving 
to set the infeed speed and the revolution speeds of the workpiece and the 
wheel respectively to V.sub.F.sbsb.2, N.sub.W.sbsb.2 and N.sub.S.sbsb.2. 
When dressing number signal n is fed to operation circuit 103, wheel 
diameter value D.sub.S is corrected with the above described formula, and 
accordingly workpiece revolution values N.sub.W.sbsb.1 and N.sub.W.sbsb.2 
and infeed speed values V.sub.F.sbsb.1 and V.sub.F.sbsb.2 are all changed 
for maintaining given K.sub.V.sbsb.1, K.sub.V.sbsb.2, .DELTA..sub.1 and 
.DELTA..sub.2. 
Therefore, regardless of the wheel diameter decreasing due to dressing 
operation, grinding operation is proceeded in optimum working condition. 
It is to be noted that modification and variation may be made in the 
invention. For instance, instead of grinding wheel revolution speeds, 
workpiece revolution speeds N.sub.W.sbsb.1 and N.sub.W.sbsb.2 may be 
preset for computing wheel revolution speed values with them in operation 
circuit 103 or grinding wheel surface speeds for rough and fine grindings 
may be preset for computing the sames N.sub.S.sbsb.1 and N.sub.S.sbsb.2 
and workpiece revolution speeds N.sub.W.sbsb.1 and N.sub.W.sbsb.2. It may 
also be available to the invention that electronic switches are connected 
between operation circuit 103 and presetting circuit 104, not to the 
output side of operation circuit 103. 
Further, in case of ordinary internal grinders which do not operate 
spark-out as is shown in FIG. 1, flip-flop 133 should be removed and 
electronic switch T.sub.33 should be operated simultaneously with switch 
T.sub.34. 
The result of experiments of grinding method according to this invention we 
have done is shown in the tables 1 and 2, in reference to the conventional 
method of constant workpiece revolution. 
In each of these experiments, equal workpieces, the same grinding machine, 
the same grinding wheel and the same grinding conditions other than what 
are shown in the table 1 or 2 are used for equitable comparison. 
Table 1 
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Conventional this invention 
rough fine rough fine 
grinding grinding grinding grinding 
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Workpiece 
revolution 
2,380 R.P.M. 3,360 960 R.P.M. 
speed N.sub.W R.P.M. 
infeed 
speed V.sub.F 
35 .mu.m/sec 
5 .mu.m/sec 
59 .mu.m/sec 
3.2 .mu.m/sec 
speed V.sub.F 
cylindricity 
.+-.1.5 .mu.m .+-.1.0 .mu.m 
surface 
raughness 1.8 .mu.m R.sub.max 
1.2 .mu. R.sub.max 
diameter 
range 4 .mu.m 3 .mu.m 
net work- 
ing time 9.2 sec. 5.7 sec. 
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Table 2 
______________________________________ 
Conventional this invention 
rough fine rough fine 
grinding 
grinding grinding grinding 
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Workpiece 
revolution 
3,750 R.P.M. 4,500 1,500 
R.P.M. R.P.M. 
speed N.sub.W (for initial wheel 
diameter) 
infeed 
speed V.sub.F 
40 .mu.m/sec 
5 .mu.m/sec 
59 .mu.m/sec 
3.2 .mu.m/sec 
cylindricity 
.+-.1.5 .mu.m .+-.0.5 .mu.m 
surface 
roughness 1.5 .mu.m R.sub.max 
1.2 .mu.m R.sub.max 
diameter 
range 4 .mu.m 2 .mu.m 
net working 
time 7.1 sec. 4.8 sec. 
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For signal P.sub.3 of the above described embodiment, a size signal P.sub.3 
from the improcess sizing device of the grinder is more preferably 
substituted for the purpose of obtaining more accurate finish size.