Infeeding method for internal grinders

Infeeding method for internal grinders has rough grinding infeeding and fine grinding infeeding speeds. The changing point from the rough grinding to the fine grinding is shifted earlier in response to the grinding wheel diameter decreasing so that the actual stock-removal rate and the work-up time for a workpiece are kept approximately constant with uniform working on the workpiece.

BACKGROUND OF THE INVENTION 
This invention relates to an internal grinder which successively operates 
at two or more kinds of predetermined infeed speed in a grinding 
operation, and more particularly to an internal grinder which selects a 
changing point from one infeed speed to another in response to the 
grinding wheel diameter change. 
Cutting ability of a grinding wheel is influenced very much by various 
grinding phenomema and parameters, and particularly by cutting angles of 
abrasive grains relative to the work surface, i.e. by the wheel diameter. 
This is well demonstrated in an infeed control method which has a 
predetermined non-constant infeed vs. time characteristic, as shown by a 
heavy line .alpha. in FIG. 1, and which has a fixed changing point A from 
rapid infeed (0 to A) to rough grinding infeed (A to B) and a fixed 
changing point B from the rough grinding infeed to fine grinding infeed (B 
to C). 
When the wheel diameter becomes smaller to some extent, the grinding 
ability is better so that the actual stock-removal of the workpiece occurs 
faster as shown by chain line .beta. in FIG. 1 to reach the point t.sub.1 
from which the fine grinding starts and the whole grinding process is 
finished at the point f.sub.1 in a shorter time, with the infeed table 
returning to c.sub.1. On the contrary, a larger wheel diameter tends to be 
accompanied by poorer grinding ability so that the actual stock removal 
occurs slower as shown by the two-dotted chain line .gamma. in FIG. 1 to 
reach at the starting point t.sub.2 of fine grinding and finish the whole 
grinding process with at f.sub.2, the infeed table returning to c.sub.2 in 
a longer time than that required with a small wheel diameter. 
A shorter cycle time of the grinding operation as the former case gives a 
grinding finish with poor cylindricity and rough surface finish, while a 
longer cycle time as the latter case requires a longer time than 
necessary. 
SUMMARY OF THE INVENTION 
Therefore, it is the principal object of the present invention to provide 
an infeeding method for internal grinders, with which the above-mentioned 
fault of the cycle time deviation caused by wheel diameter variation is 
perfectly eliminated. 
This and other objects are attained by a method in which the changing 
points, from rapid infeed to rough grinding infeed and from rough grinding 
infeed to fine grinding infeed, are adjusted in response to the wheel 
diameter, whereby every grinding operation is finished almost in a same 
cycle time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now, an embodiment of this invention applied on an internal grinder will be 
described referring to FIGS. 2 and 3. 
FIG. 2 is a block diagram showing an embodiment of the infeeding method of 
the invention, in which reference numeral 1 designates an internal grinder 
which is provided with a grinding wheel spindle device 4 mounted on a bed 
2 by way of a slide table 3 and an infeeding table 6 mounted on bed 2 by 
way of a table stand 5. Infeeding table 6 is slidable in a perpendicular 
direction relative to the sliding direction of wheel spindle device 4 and 
is driven by an infeeding device 7 provided in bed 2. 
A workpiece W is held in a work spindle device which is mounted on 
infeeding table 6 but is not shown in the drawing. Reference numeral 8 is 
an inprocess size measuring device mounted on infeeding table 6. This size 
measuring device 8 continuously measures the workpiece diameter while the 
workpiece is worked by the grinding wheel of the wheel spindle device 4. 
Reference numeral 9 designates a location or position detecting device 
mounted on table stand 5 to detect the location or position of infeeding 
table 6. The detected signal from location detecting device 9 is amplified 
by an amplifier 10 to be the location signal a of infeeding table 6. This 
location signal a and a compensating value b set by a compensating value 
setting circuit 12 which will be described hereinafter are inputs of an 
operation circuit 11. The output sum a + b is fed to a pair of comparing 
or comparator circuits 13 and 14. Comparing circuit 13 generates output 
Q.sub.1 when the output a + b of operation circuit 11 reaches at standard 
value P.sub.1 (i.e. location signal a reaches at a value of P.sub.1 - b), 
while comparing circuit 14 generates output Q.sub.2 when the output a + b 
of operation circuit 11 reaches another standard value P.sub.2 (i.e. 
location signal a reaches P.sub.2 - b). 
The outputs Q.sub.1 and Q.sub.2 are fed to an infeed control circuit 15 
which controls infeeding device 7, signal Q.sub.1 being used as the 
changing signal to change from the rapid infeed speed to the rough 
grinding infeed speed and signal Q.sub.2 being used as the changing signal 
to change from the rough grinding infeed speed to the fine grinding infeed 
speed. 
Reference numeral 16 designates an amplifier to amplify the output of 
inprocess size measuring device 8 into a workpiece size signal, which is 
compared with a predetermined finish size value in a comparing circuit 17. 
This comparing circuit 17 generates output Q.sub.c and applies it to 
infeed control circuit 15 when the workpiece size signal reaches the 
finish size value, i.e. when the workpiece diameter reaches the finish 
size. This output signal Q.sub.c makes infeed control circuit 15 stop 
infeed and return infeeding table 6 to its initial position. 
Said compensating value setting circuit 12 changes its output level of 
compensating value b in response to the wheel diameter value fed from a 
wheel diameter operation circuit 18 which generates the wheel diameter 
with the initial diameter of the wheel and dressing amount. The dressing 
amount is attained from the dressing infeed of the dressing device. If the 
dressing depth for every dressing is constant, the wheel diameter can be 
computed with the dressing number. 
The operation in the above-mentioned infeed method according to this 
invention will now be described hereinafter. 
When the wheel diameter is initially D.sub.0, the compensating value 
setting circuit 12 generates b.sub.0 which is rather large and corresponds 
to the larger diameter D.sub.0. In this state, infeed table 6 is rapid fed 
until the location signal a of the infeed table reaches at P.sub.1 - 
b.sub.0, and then, the infeed table 6 is fed in at the rough grinding 
infeed speed until the signal a reaches at P.sub.2 - b.sub.0 where infeed 
table 6 is thereafter fed in at the fine grinding infeed speed as shown by 
line l in FIG. 3. With this infeed movement of infeed table 6, actual 
stock removal of the workpiece W is performed on a line as l'. When the 
workpiece diameter reaches the finish size, infeed table 6 returns quickly 
to C.sub.1 '. 
When the wheel diameter has decreases to D.sub.1 with dressing or other 
wear, the compensating value setting circuit 12 generates a smaller value 
b.sub.1 corresponding to the smaller wheel diameter D.sub.1. In this 
state, infeed table 6 is rapid fed till the location signal a reaches at 
P.sub.1 - b.sub.1, and then, is changed to be fed with rough grinding 
infeed speed till the signal a reaches at P.sub.2 - b.sub.1 where infeed 
table 6 is changed to be fed in at the fine grinding infeed speed as shown 
by dotted line m in FIG. 3. With this infeed movement of infeed table 6, 
actual stock removal of the workpiece is performed on a line m' which is 
near line l'. That is, in this case, the infeed speed changing points are 
shifted to occur before the changing points for the larger wheel case. 
Thus, infeed table 6 returns to C.sub.2 ' after finishing wheel diameter. 
The smaller the wheel diameter becomes with higher its grinding ability, 
the earlier the changing points shift gradually, whereby, actual stock 
removal of the workpiece is performed with an almost constant rate and 
cycle time.