Grinding machine with CNC pivotable workhead

A grinding machine is provided with a workhead support means having pivotable shaft means on which the support means is pivoted by a servomotor/pinion arrangement controlled by a programmable controller and a position indicating means on the pivotable shaft means that inputs angular shaft position signals to the controller. Adaptive control components may also be included in the control arrangement. The workhead support means is thereby pivotable to vary the angular relationship of the workpart axis to the grinding wheel axis to effect a desired taper or contour grind or to compensate for changes in grinding parameters causing out of tolerance ground workparts. Special releasable clamps are provided to fix a desired position of the workhead support means and yet release same for pivoting movement. Fluid lift mechanisms are also provided to reduce friction between the workhead support means and the adjacent machine base member during pivoting.

FIELD OF THE INVENTION 
The present invention relates to grinding machines and, in particular, to 
grinding machines having means to adjust the positional relationship 
between a grinding wheel carried on a wheelhead and a workpart held on a 
workhead especially in a programmed or adaptively controlled manner. 
BACKGROUND OF THE INVENTION 
In the known centerless grinding process for workparts such as bearing 
raceways, the axes of the workpart and grinding wheel may have to be 
varied relative to one another in some cases to grind a particular taper 
on the workpart and in other cases to compensate for wheel deflection or 
wear or other fluctuations in grinding process parameters during a run 
causing out of tolerance workparts. 
In one commercially available centerless grinding machine, the ability to 
adjust the axes of the workpart and grinding wheel is provided by mounting 
the workhead on a pivotable plate. The plate is pivotable about a 
stationary pivot stud extending between the plate and a cross-slide 
mounted on the machine base. The cross-slide includes a semi-circular 
shaped inverted T-slot to receive a pair of T-nuts. Locking screws extend 
from the workhead into the T-nuts and are manually tightened to lock the 
position of the workhead and thus the orientation of the workpart axis 
relative to the axis of the grinding wheel mounted on another cross-slide. 
Other than the placement of lubricant between the workhead support plate 
and cross-slide supporting the plate, no provision is made for reducing 
friction therebetween during pivoting. 
To vary the relationship of the workpart axis and grinding wheel axis from 
parallel to angular to intentionally taper grind or to compensate for 
changes in grinding parameters, the operator must manually loosen the 
locking screws and manually turn an adjusting screw which is screw mounted 
on the workhead cross-slide and engages the support plate. As the 
adjusting screw is turned, the support plate is pivoted about the pivot 
stud to the desired position. An indicator dial driven by the rotation of 
the adjusting screw can be read to determine when the angular relationship 
of the workpart axis to the grinding wheel axis is established. 
Thereafter, the locking screws are re-tightened by the operator to 
maintain the adjusted position. Of course, this adjustment sequence for 
placing the workpart axis and grinding wheel axis in related angular 
relationship is time consuming and costly. 
U.S. Pat. No. 3,874,121 issued Apr. 1, 1975 shows an internal grinding 
machine having a swivel base on which a spindle is carried so that the 
spindle axis can be adjusted angularly. 
U.S. Pat. Nos. 4,186,529 and 4,115,956, issued Feb. 5, 1980 and Sept. 26, 
1978, respectively, illustrate a programmably controlled machine with a 
grinding wheel support system and workpart support system each having a 
plurality of slides and cross-slides and a rotary table driven by 
individual servomotors for grinding end cutting tools and the like. 
U.S. Pat. No. 4,293,913, issued Oct. 6, 1981, discloses a numerical 
controller for a grinding machine for cylindrical workparts. 
SUMMARY OF THE INVENTION 
The present invention in a typical working embodiment provides a grinding 
machine having (a) a workhead support means with a pivotable means, such 
as a pivotably mounted shaft, on which the workhead support means is 
pivoted to vary the angular relationship of the workpart axis relative to 
the grinding wheel axis, (b) a means such as a servomotor/pinion 
arrangement for pivoting the workhead support means and the pivotable 
shaft means and (c) a means for controlling the angular position of the 
workhead support means and workhead thereon including position indicating 
means for determining the angular position of the workpart axis by 
determining angular or rotational movement of the pivotable means of the 
workhead support means with respect to a reference position and means for 
actuating the pivoting means until the position indicating means indicates 
that a position is reached corresponding to a desired angular relationship 
of the workpart axis to the grinding wheel axis. 
The controlling means preferably includes a programmable controller and the 
pivoting means, such as the servomotor, is under the control of the 
programmable controller so as to pivot the workhead support means in an 
incremental step sequence or in a substantially continuous manner until 
the position indicating means indicates that a position is reached 
corresponding to a programmed angular relationship of the workpart axis to 
the grinding wheel axis. 
Preferably, the position indicating means comprises a rotor of a feedback 
transducer connected to the pivotable shaft means of the workhead support 
means and an adjacent stator connected to a fixed machine member, thereby 
providing minimal looseness and elastic wind-up in the position indicating 
system and reduction of angular positioning errors associated therewith. 
In one embodiment of the invention, the controlling means also includes an 
adaptive control system having a gaging means for measuring one or more 
grinding parameters and the servomotor is responsive to the gaging means 
to pivot the workhead support means until the position indicating means 
indicates that a position is reached corresponding to an angular relation 
of the workpart axis to the grinding wheel axis providing the desired 
grinding parameter. 
In a particularly preferred embodiment of the invention, a releasable clamp 
means is provided between the workhead support means and machine base 
means for clamping the support means to the machine base means to maintain 
a desired position and yet is releasable to allow pivoting of the support 
means relative to the base means to another position. 
In still another particularly preferred embodiment of the invention, a lift 
means such as fluid pressure means is provided between the workhead 
support means and the machine base means to reduce friction therebetween 
during pivoting of the support means, assuring that the servomotor 
pivoting means can position the support means to within the resolution of 
the positioning indicating means. 
Other object and advantages of the present invention will be apparent to 
those skilled in the art in view of the following drawings and detailed 
description.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows in partial view a grinding machine constructed in accordance 
with the present invention for grinding the internal diameter of annular 
workpart W which may be for example a bearing raceway. It is apparent that 
the grinding machine includes a wheelhead 2 in which a rotatable spindle 4 
having a grinding wheel 6 is rotatably supported in known manner and 
driven by known means such as electric motor/drive belt arrangement (not 
shown). The wheelhead 2 is mounted such as by bolts 8 on a transverse 
support member 10 that is moved on a transverse cross-slide member 13 for 
movement transverse to workpart W. Slide 13 in turn is supported on a 
longitudinal slide (not shown) for movement toward or away from workpart 
W. 
The workpart W is held to a magnetic chuck 20 or other workpart holding or 
fixturing device rotatably mounted on the workhead 22. The workhead 22 in 
turn is bolted or otherwise attached to workhead support plate 24 which is 
pivotably mounted on base member 26 by a pivotable shaft/bearing 
arrangement 28 described in more detail herebelow. 
The workhead support plate 24 is shown in FIG. 6 and the pivotable 
shaft/bearing arrangement 28 for pivotably mounting the plate 24 on base 
member 26 is shown in FIG. 4 and in more detail in FIG. 5. It is apparent 
that the pivotable arrangement 28 includes a central pivot shaft or 
spindle 30 rotatably or pivotably supported vertically in tubular portion 
25 of secondary base member 27 by two bearings 32, 34 having inner races 
32a, 34a, outer races 32b, 34b and balls 32c, 34c therebetween and spacers 
33. The secondary base member 27 is bolted to the base 26. The bearing 32 
is positioned at its lower end by locking collars 36, 38, collar 38 being 
threaded to the secondary base portion 27. Bearing 34 is positioned at its 
upper end by an inwardly extending radial shoulder 25a on the tubular base 
portion 25. 
The support plate 24 is affixed to the pivotable shaft 30 by means of cap 
screw 40 threaded to the shaft as shown and truncated conical annular 
bushings 42, 44 which are engaged by the cap lip 40a and wedged axially 
against the shaft shoulder 30a supported by bearings 32, 34 and radially 
against the wall defining bore 24a in the plate 24 to center the pivot 
shaft on spindle 30. As a result, the bushings 42, 44, as compressed, 
reduce radial and axial movement between the plate and shaft to a minimum 
at the connection. 
FIG. 11, in which like numerals primed represent like features, illustrates 
an even more preferred technique for affixing the support plate 24' to the 
pivot shaft or spindle 30'. In particular, the support plate includes a 
plurality of bores 31' (only one shown) partially threaded along their 
lengths and spaced circumferentially around the bore 24a' in the plate. 
The pivot shaft or spindle 30' includes a small diameter shoulder 30a' 
supported by the bearings 32', 34' with an annular seal 41' preventing 
foreign matter from entering the bearings and a larger diameter shoulder 
30b' having a plurality of threaded bores 30c' coaxially aligned with 
bores 31' in the support plate 24'. A threaded screw 37' is threadably 
received in the aligned bores 31' and 30c' to attach the support plate to 
the large diameter shoulder 30b'. Cap screw 40' and bushings 42', 44' 
function to center the shaft 30' in the plate bore 24a'. This support 
plate/pivot shaft arrangement is capable of withstanding an impact force, 
such as one that might occur during a machine malfunction, without a 
position error occurring. 
The lower end of shaft 30 includes an end cap 50 attached as by screws 52 
(only one shown) to the shaft and by screws 54 (only one shown) to an 
annular rotor 60 of a rotary position feedback transducer system. The 
rotor 60 is thereby directly attached to the shaft 30 and pivotable or 
rotatable with the shaft 30 and plate 24. An annular stator 62 is shown 
affixed to secondary base member 27 by screws 64 (only one shown) in 
spaced axial relation to the rotor. 
As shown in FIG. 8, a helical return spring 70 is attached to the cap 50 
and stator 62 by clamps 72, 74, respectively, and lead wires 75, 76 are 
attached to the rotor and stator and extend to feedback transducer 80 
shown in FIGS. 1, 2 and 4. The rotor, stator and feedback transducer are 
of the commercially available type such as "INDUCTOSYN" rotary position 
transducer system available from Farrand Industries Inc. of 99 Wall 
Street, Valhalla, New York 10595 and will be described in further detail 
hereinbelow. 
The support plate 24 includes a network of lubrication channels 82 
concentric around the bore 24a thereof receiving the shaft 30, caps 40 and 
bushings 42, 44. Lubricant is introduced through opening 86 and passage 88 
and exits through opening 90 extending from the bottom to the top of the 
support plate to an exit fitting (not shown). 
The other end of the workhead support plate 24 includes a set of channels 
92, 94. Each channel includes opening 92a, 94a on opposite sides of the 
support plate 24 extending from the bottom of the plate to lateral 
passages 93 connected to an inlet fitting 95 and lubricant inlet fitting 
97, FIG. 9. Pressurized air, e.g. 15 psi, is fed to the entrance openings 
92a, 94a and functions in the channels to exert a lifting force on the 
support plate upward (in FIGS. 4 and 9) to reduce friction between the 
plate 24 and base member 26. It is apparent that the plate 24, base member 
26 and channels 92, 94 form a lift means therebetween. Sealing to prevent 
pressurized air leakage from between the support plate 24 and base member 
is not necessary since lift of plate 24 does not actually occur. The mass 
of and on plate 24 is counterbalanced by air pressure to reduce friction. 
Leakage is minimal as a result of non-uniformities in the surface of base 
26. The pressurized air or other fluid enters the openings 92a, 94a from 
the air inlet fittings 95 on the top of the plate and connected to a 
suitable source of air pressure. Of course, pressurized air is introduced 
into channels 92, 94 during pivoting of the support plate 24 to reduce 
friction. For example, the air lift mechanism described is designed to 
counter or bias about 95% of the mass or weight of the workhead and 
support plate. When the support plate is in position, the air pressure may 
be discontinued to eliminate the lifting force on the plate and allow 
clamping to be effected as discussed hereinbelow. 
During clamping periods, lubricant may be introduced into channels 92, 94 
through the same entrance openings 92a, 94a from lubricant inlet fittings 
97 connected to a suitable lubricant source (not shown) such as an oil 
mist source. A conventional value arrangement (not shown) is used to 
alternately shut off the pressurized air flow or lubricant flow as 
required. 
The workhead support plate ends in circular arc portion 102 having gear 
teeth 104 along the arc driven by the ing driving pinion 108, FIG. 2. The 
pinion 108 in turn is driven by a servomotor 110 connected to the pinion 
by a coupling 112 having slots 112a to provide flexibility to accommodate 
alignment errors between the servomotor output shaft 110a and input shaft 
114a of gear reducer 114. Shims 113 are provided to help in obtaining 
proper alignment. The pinion 108 is disposed in cylindrical housing 115 
and is rotatably supported therein by bearing 117 and driven by output 
shaft 114b of the gear reducer. There is a shear pin (not shown) between 
pinion 108 and output shaft 114b of gear reducer 114. A cover 121 is 
provided as shown to keep dirt and foreign matter out of these components. 
Attached to opposite sides of the workhead support plate 24 are a first arm 
120 and a second arm 122 which function to actuate proximity switch 124 as 
the support plate is pivoted. In this way, the extent of clockwise and 
counterclockwise rotation or pivoting of support plate 24 is controlled by 
shutting off servomotor 110 when the limits of movement dictated by the 
arms 120, 122 have been reached. The arms 120, 122 are affixed to the 
support plate 24 by screws 130, 132 respectively. With the arrangement 
shown, the support plate 24 is capable of pivotable movement up to 
45.degree. in the clockwise direction and 5.degree. in the 
counterclockwise direction. 
Also attached to opposite sides of the workhead support plate 24 
intermediate its length are brackets 136, 138. A flexible bellows-like 
member 140, 142 is attached at one end to the brackets 136, 138, 
respectively, and at the other end to brackets (not shown) on the machine 
base member 26. It is apparent that one of the bellows memnbers 140, 142 
will be expanded while the other is compressed when the support plate 24 
is pivoted. The bellows members function to keep dust, dirt and foreign 
matter out of slots 150, 152 in the base member 26. Slots 150, 152 are 
configured in circular arcs for purposes to be described. 
As shown in FIG. 2, the workhead support plate 24 includes a pair of 
releasable clamps 160 shown in more detail in FIG. 7. Each clamp 160 
includes a lever 162 pivotable about a shaft 164 mounted in the support 
plate 24 and including a first cam surface 166 and second cam surface 68 
at opposite ends. The cam surface 166 is engaged by a piston 170 having 
O-ring seal 172. The piston rides in a circular counterbore 174 and is 
pressurized by air or other fluid pressure to cause the piston to move in 
the bore. Air pressure is supplied by passages 176 in the support plate 24 
extending to a fitting (not shown) at the circular arc portion thereof. A 
suitable source of air pressure is connected to each fitting. 
The second cam surface 168 engages the head 180 screwed into the shaft 182 
of a T-shaped plunger 184 received in slot 150 in plate 24. The head 180 
is disposed in a circular counterbore 186 in the support plate and an 
annular spacer 190 and annular spring washers 192 are located between the 
head 180 and bottom of the counterbore 186 as shown. 
Similarly, the head 184a of the T-shaped plunger 184 is located in a 
circular counterbore 194 in the base member 26 and is spaced from the top 
of the counterbore by a spherical washer 196 and equalizing washer 198. 
Each clamp 160 includes a cover 199 attached to the top of the support 
plate 24. 
Each clamp 160 is operable to clamp the workhead support plate 24 to the 
base member 26 when the air pressure to counterbore 174 is released so 
that the force of spring washers 192 can exert a clamping force between 
the support plate 24 and base member 26 through the head 180 and T-shaped 
plunger 184. The clamping force is released by pressurizing the 
counterbore 174 to cause the piston 170 to move upwardly in FIG. 7 and 
cause the lever 172 to pivot counterclockwise about shaft 164 and depress 
the head 180 against the force of the spring washers 192. This action 
disengages the head 184a of the plunger from the spherical washer 196, 
releasing the clamping force between support plate 24 and base member 26. 
During pivoting of support plate 24, the shaft 182 of plunger 184 is 
carried through slot 152 in the base member 26. 
As mentioned hereinabove, the machine control means includes a rotary 
position feedback transducer arrangement with rotor 60 affixed to pivot 
shaft 30 and rotatable therewith and stator 62 affixed to the machine base 
26 adjacent but spaced from the rotor. The rotor and stator are each 
connected electrically to the feedback transducer 80 which as mentioned is 
available under the name "INDUCTOSYN" from Farrand Controls, a division of 
Farrand Industries Inc. of 99 Wall Street, Valhalla, New York 10595. The 
feedback transducer arrangement incorporates an "absolute zero" proximity 
switch 200 including a switch actuator arm 202 affixed to the front (FIG. 
4 or left side in FIG. 2) side of the workhead support plate 24 by bracket 
204 and screws 206. The pulse received from the rotor/stator arrangement 
next after the switch 200 signals during travel in one direction is taken 
as the arbitrary "zero" reference for all angle measurements. With the 
feedback transducer described, the support plate 24 can be positioned 
within plus or minus 4 arc seconds of resolution. 
The control means also includes a suitable controller 212, programmable or 
other types, which receives signals from the feedback transducer 80 
regarding angular position of the workhead support plate 24 and which 
processes these signals into selected programs stored in the controller 
memory in known fashion. The programmable controller in one mode of 
operation may dictate a discrete charge in angular position, either at the 
start of a run of workparts requiring a taper angle different from that 
required by a previous run of workparts or during the run to provide 
different taper angles on the same workpart. Typically in the latter 
situation, the controller 212 would have stored thereon grinding programs 
for several different configurations of workparts. And, the controller 212 
could be programmed to control the servomotor 110 to drive the workhead 
support plate 24 in a substantially continuous angular pivoting manner to 
provide contour workpart grinding. In this situation, the clamps 160 would 
be released during pivoting and the air lift fixture would either not be 
used or would be used at possibly a reduced level. 
In another mode of operation, a gaging means 216, for example, including 
gaging fingers 217 or other mechanisms to determine the inner diameter of 
workpart W is employed on the machine to measure the actual angle ground 
on the workpart surface and inputs signals to the controller 212. Or, the 
gaging means could measure some other process parameter such as grinding 
force or coolant temperature. Such gaging means are known in the art. The 
signals from the gaging means would be fed to the controller with an 
adaptive control system so that the controller varies the angular position 
of the workhead support plate 24 to bring the measured parameter to the 
desired value. 
Any suitable programmable controller may be used, such as a TEACHABLE II 
programmable controller available from Bryant Grinder Corporation, 
Springfield, Vermont, the assignee hereof. Other controllers useful in the 
invention include known electronic positioning control systems such as CNC 
(computer numerical control) and NC (numerical control). Suitable 
controllers include Allen Bradley 7300 CNC, Bendix System 5 CNC or Modicon 
2184 controllers. 
The servomotor 110 may be driven through any suitable servo drive unit 220 
such as, for example, a servo drive of Hyper Loop, Inc. of 7459 West 79th 
Street, Bridgeview, Illinois 60455, sold under the trademark "HYAMP". The 
"HYAMP" servo drive is a single-phase, four wave, bidirectional SCR 
controlled servo drive for D.C. motors, and it provides D.C. drive power 
for precise speed control and regulation over a wide spaced range. Another 
suitable servo-Drive, designated as Size 50, is available from General 
Electric Company, 685 West Rio Road, Charlottesville, Virginia 22906. 
While the grinding machine of the invention has been described above as 
having a workhead support plate pivotable over a 50.degree. range, it will 
be understood that lesser or greater angular movement may be provided 
including a workhead support plate which is pivotable or rotatable 
360.degree.. Furthermore, the position indicating means may comprise other 
known systems for sensing angular movement such as known laser feedback 
systems for excellent position accuracy and also known encoder feedback 
systems. 
While the grinding machine of the invention has been described by a 
detailed description of certain specific and preferred embodiments, it is 
understood that various modifications and changes can be made in any of 
them within the scope of the appended claims which are intended to also 
include equivalents of such embodiments.