U.S. patent number 3,913,277 [Application Number 05/465,237] was granted by the patent office on 1975-10-21 for grinding machine.
This patent grant is currently assigned to Cincinnati Milacron-Heald Corporation. Invention is credited to Robert S. Hahn, Richard P. Lindsay.
United States Patent |
3,913,277 |
Hahn , et al. |
October 21, 1975 |
Grinding machine
Abstract
This invention relates to a grinding machine making use of a
closed-loop control of grinding force. In the control system, data
on wheel size and wheel dullness are used to continuously determine
grinding rate.
Inventors: |
Hahn; Robert S. (Northboro,
MA), Lindsay; Richard P. (Marlboro, MA) |
Assignee: |
Cincinnati Milacron-Heald
Corporation (Worcester, MA)
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Family
ID: |
26963293 |
Appl.
No.: |
05/465,237 |
Filed: |
April 29, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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285628 |
Sep 1, 1972 |
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94389 |
Dec 2, 1970 |
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Current U.S.
Class: |
451/8; 451/21;
451/26; 451/294; 451/295 |
Current CPC
Class: |
B23Q
15/12 (20130101); B24B 49/16 (20130101) |
Current International
Class: |
B23Q
15/007 (20060101); B23Q 15/12 (20060101); B24B
49/16 (20060101); B24B 049/10 () |
Field of
Search: |
;51/165R,165.71,165.77,165.8,165.82-165.86,165.9-165.92,139,134.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Whitehead; Harold D.
Attorney, Agent or Firm: Blodgett; Norman S. Blodgett; Gerry
A.
Parent Case Text
This is a continuation of application Ser. No. 285,628 filed Sept.
l, 1972, which is a continuation of application Ser. No. 94,389
filed Dec. 2, 1970.
Claims
The invention having been thus described, what is claimed as new
and desired to secure by Letters Patent is:
1. A grinding machine for producing a surface of revolution on a
workpiece, comprising:
a. a base,
b. a table carrying a wheelhead with a spindle and abrasive wheel
mounted on the base,
c. means for mounting the workpiece on the base,
d. feed means to bring about relative movement between the tables
and the base transversely of the spindle to bring about an
instantaneous force between the wheel and the workpiece to cause a
grinding action between the wheel and the workpiece,
e. a gage for measuring the instantaneous force between the wheel
and the workpiece,
f. a sensing system adapted to determine the wheel size and the
wheel dullness and to generate signals indicative of these physical
characteristics, and
g. a feed-back control receiving a combined signal from the gage
and the sensing system, and operative, when the combined signal
varies from a predetermined value, to adjust the feed means.
Description
BACKGROUND OF THE INVENTION
In the operation of a grinding machine, there are several
advantages to operating in such a manner that the force is
controlled at a predetermined value and the rate of feed is allowed
to vary uncontrollably. However, there are also attendant
disadvantages, particularly where the machine used is an internal
grinding machine; in that case, the abrasive wheel is mounted on a
cantilevered spindle and is subject to considerable bending. There
are so many variables that enter into the determination of the
actual grinding force between the wheel and the workpiece that all
kinds of problems are presented. The simplest method of controlling
the force is to use a hydraulic cylinder for cross-feed and to
control the oil pressure in the cylinder. In a rough way (assuming
that there is no friction in the cross-slide), the force between
the abrasive wheel and the workpiece is proportional to the
pressure of the oil in the cylinder. However, as a practical
matter, a number of variables enter into the picture that destroy
this simple relationship. The sharpness or cutting ability of a
wheel can vary from time to time and from wheel to wheel. The
nature of the material being ground also varies. The force changes
when the size of the wheel changes as it is dressed down from one
grinding cycle to the next. Variation in force between the abrasive
wheel and the workpiece can cause variation in taper in the
finished ground surface and so on. These and other difficulties
experienced with the prior art devices have been obviated in a
novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide
a grinding machine having a control for maintaining the force
between the abrasive wheel and the workpiece at a constant
perdetermined value.
Another object of this invention is the provision of an internal
grinding machine in which taper and surface finish can be
maintained at a predetermined value.
A further object of the present invention is the provision of a
grinding machine having a closed-loop force control which is
relatively simple in construction and operation.
With these and other objects in view, as will be apparent to those
skilled in the art, the invention resides in the combination of
parts set forth in the specification and covered by the claims
appended hereto.
SUMMARY OF THE INVENTION
In general, the invention has to do with a grinding machine having
a base, having a table carrying a wheelhead with a spindle and
abrasive wheel mounted on the base, and having a table carrying a
workhead with a workpiece mounted on the base. Feed means is
provided to bring about relative movement between the tables
transversely of the spindle to cause a grinding action between the
wheel and the workpiece. A gage is provided for measuring the
instantaneous force between the wheel and the workpiece and a
feed-back control receives a signal from the gage and is operative,
when the signal varies from a predetermined value; to adjust the
feed means.
BRIEF DESCRIPTION OF THE DRAWINGS
The character of the invention, however, may be best understood by
reference to one of its structural forms, as illustrated by the
accompanying drawings, in which:
FIG. 1 is a schematic view of a grinding machine and its controls
built in accordance with the principles of the present invention,
and
FIG. 2 is a schematic view of the operative portions of the
grinding machine.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 it can be seen that the grinding machine, indicated
generally by the reference numeral in 10 includes a feed cylinder
11 which receives a constant hydraulic pressure from a source 12.
The feed cylinder 11 is operative on the grinding process 13, as
indicated by a line 14. The grinding process is also affected by
the system spring constant K indicated by the box 15. The spring
constant K is shown in FIG. 2 as the combined spring constant of
the machine and constitutes the sum of Kw, Ks, and Kg. For the
purpose of demonstrating control logic, a line 16 leads from the
box 15 to a signal junction 17 to show that the grinding process 13
is affected both by the system spring constant and by the force
from the feed cylinder 11. A damper box 18 is connected to the
grinding process 13 and to the junction 17 to show the manner in
which the damper effects the grinding process.
A line 19 extends from the source 12 to a diaphragmtype force
measuring device 21 of the type shown in the U.S. Pat. No.
3,618,269, dated Nov. 9, 1971. This device contains a diaphragm
which receives the same oil pressure as the feed cylinder 11, the
other side of the diaphragm receiving the full grinding force of
the machine. A strain gage mounted on the diaphragm gives a signal
indicative of the grinding force and this appears on the line 22
and is applied to one inlet of the junction 23. The other inlet
receives a signal from the system K box 15 through a line 24. The
combined effects of the grinding process force and the signal from
the diaphragm 21 is felt by the force transducer 25 which is
amplified in the amplifier 26 resulting in a signal on a line 27.
This signal passes along a line 28 to a wheel dullness indicator 29
and along a line 31 to a junction 32.
The signal from the junction 32 is introduced into an error signal
amplifier 33 whose output signal is introduced to a pulse generator
34. The ouput of the pulse generator 34 appears on a line 35
leading to a stepping motor drive 36 which operates through a gear
train and ball screw apparatus 37 which, in turn, operates through
a junction 38 whose signal is felt in the system K box 15.
The output line 35 of the pulse generator 34 is connected by a line
39 which is connected to the input of the wheel dullness indicator
29. The output of this indicator appears on a line 41 which is
connected to a junction 42. Also connected to the junction 42 is a
force reference box 43 and a line 44 leading from a modulation
attenuator 45. This attenuator receives a signal from a wheel size
indicator 46 which, in turn, receives a signal from a compensation
slide indicator 47. The wheel size indicator 46 is of the type
shown and described in the patent application of Robillard Ser. No.
877,092, filed Nov. 17, 1969, now U.S. Pat. No. 3,601,930 dated
Aug. 31, 1971. The wheel dullness indicator 29 is of the type shown
and described in the U.S. Pat. No. 3,745,710, dated July 17,
1973.
The output of the junction 42 appears on a line 48 which is
introduced into a high force attenuator 49, an intermediate force
attenuator 51, a low force attenuator 52, and a final force
attenuator 53. The high force attenuator 49 feeds into an R-C
shaping network 54 and from there through a normally closed
contactor 55 and a normally open contactor 56 (which is always
closed during grinding) into the junction 32. The intermediate
force attenuator 51 is connected through a normally closed
contactor 57 and a normally open contactor 58 to a point between
the contactors 55 and 56. The low force attenuator 52 is connected
through a normally closed contactor 59 and a normally open
contactor 61 to a point between the contactors 57 and 58. The final
force attenuator 53 is connected through a normally open contactor
62 to a point between the contactors 59 and 61. The contactors 55
and 58 form part of the same relay and, therefore, change condition
at the same time. Similarly, the contactors 57 and 61 form part of
the same relay as do the contactors 59 and 62.
FIG. 2 shows somewhat schematically a grinding machine with which
the control of FIG. 1 is used. It can be seen that the wheelhead
table 63 has a mass m and is pressed rearwardly by the feed
cylinder 73 as it travels over 18. base 64. The travel is damped by
damper 18 The table carries a spindle 65 with an abrasive wheel 66
mounted thereon. The wheel operates on the surface of a workpiece
67 which, in turn, is mounted on the base 64. The table 63 has a
retractable stop 68 operated by a stepping motor 69. This stop
engages on occasion the diaphragm 21 mounted on the compensation
slide 70. The compensation slide is moved relative to the base 64
by means of a screw 71 operated by a stepping motor 72. The same
pressure oil that appears behind the diaphragm 21 also operates the
feed cylinder 73.
It is obvious that the minor changes may be made in the form and
construction of the invention without departing from the material
spirit thereof. It is not, however, desired to confine the
invention to the exact from herein shown and described, but it is
desired to include all such as properly come within the scope
claimed.
* * * * *