US3552066A

US3552066A - Grinding machines

Info

Publication number: US3552066A
Application number: US796705A
Authority: US
Inventors: Robert Gladstone
Original assignee: Wiggins Teape Research and Development Ltd
Current assignee: Arjo Wiggins Ltd
Priority date: 1969-01-27
Filing date: 1969-02-05
Publication date: 1971-01-05
Anticipated expiration: 1988-01-05
Also published as: GB1261071A

Abstract

A GRINDING MACHINE COMPRISES A GRINDING A WHEEL FOR GRINDING A CIRCUMFERENTIAL SURFACE OF A WORKPIECE OF CIRCULAR CROSS-SECTION SUCH AS A STEEL ROLL, TRAVERSING MEANS ADAPTED TO EFFECT RELATIVE LONGITUDINAL TRAVERSING MOVEMENT IN THE DIRECTION OF THE AXIS OF THE WORKPIECE, BETWEEN THE GRINDING WHEEL AND THE WORKPIECE, ROTARY MEANS FOR ROTATING THE WORKPIECE WHILE IT IS BEING GROUND, GAUGING MEANS FOR DETERMINING, WHILE THE GRINDING WHEEL IS GRINDING THE WORKPIECE, ANY DIFFERENCE BETWEEN A DATUM VALUE AND THE DIAMETER OF THE PARTICULAR CIRCUMFERENCE OF THE WORKPIECE ON WHICH THE GRINDING WHEEL IS ACTING MEANS, CONTROLLED BY THE GAUGING MEANS, FOR ADJUSTING THE POSITION OF THE GRINDING WHEEL IN A SENSE TO BRING SAID DIFFERENCE TO A PREDETERMINED VALUE, A MOVABLE DATUM MEMBER PROVIDING SAID DATUM VALUE, A CAM ROTATION OF WHICH IS ADAPTED TO EFFECT ADJUSTMENT OF THE POSITION OF SAID DATUM MEMBER, THEREBY ADJUSTING THE DATUM VALUE, CONTROL MEANS, ACTUATED BY THE TRAVERSING MEANS, AND

CONTROLLING THE CAM DRIVING MEANS IN A MANNER TO RELATE THE ROTATIONAL POSITION OF THE CAM TO THE POSITION OF THE TRAVERSING MEANS, THE CONTROL MEANS BEING ADJUSTABLE IN A MANNER TO VARY THE RELATION BETWEEN THE ROTATIONAL POSITION OF THE CAM AND THE POSITION OF THE TRAVERSING MEANS.

Description

R. AGLADSTONE GRINDING MACHINES klan. f5, 1'971 9 Sheets-Sheet l Filed Feb. 5, 1969 Inventor Robert Gladstone rey? o Jan. 5, 1971 Filed Feb. 5, 1969 R. GLADsToNE 3552,06

GRINDING MACHINES 9 sheets-sheet 2 o5 Inventor Robert Gladstone s T C m A m Lm I R Jan. 5, 1971 9 Sheets-Sheet 5 Filed Feb. 5 1969 Jan. 5, 1971 l GLAbsTQNE GRINDING MACHINES 9 Sheets-Sheet A Filed Feb. 5 1969 Inventor Robert Gladstone j; I My g/Q45@ Jan. 5, 1971 R. GLADsToNE GRINDING MACHINES 9 Sheets-Sheet 5 Filed Feb. 5 1969 Inventor Robert Gludsone Z/fA 1&11'151971 'l R. GLADsToNE 3552,96

GRINDING MACHINES Filed Feb. 5, 1969 9 Sheets-Sheet 6 Inventor Robert Gladstone Jan. 5, 1971 R. GLADsToNE 3,552,065

GRINDING MACHINES Filed Feb. s, 1969 9 sheets-sheet 7 I 75 DDD "W lnvenior D00 O q Robert Gludsone /f/Q; @Wwf/yf' 'j "Tilt 1971 l R. GLADSTON 3,552,066

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GRINDING lvLAcnLIINEs` Filed Feb. 1969 9 sheets-sheet 9 Inventor Robert Gladstone Und States Patent 3,552,066 GRINDING MACHINES Robert Gladstone, Weybridge, Surrey, England, asslgnor to Wiggins Teape Research & Development Limited, London, England, a British company Filed Feb. 5, 1969, Ser. No. 796,705

Int. Cl. B24b 5/04 U.S. Cl. 51-49 6 Claims ABSTRACT F THE DISCLOSURE A grinding machine comprises a grinding wheel for grinding a circumferential surface of a workpiece of circular cross-section such as a steel roll; traversing means adapted to effect relative longitudinal traversing movement in the direction of the axis of the workpiece, between the grinding wheel and the workpiece; rotary means for rotating the workpiece while it is being ground; gauging means for determining, while the grinding wheel is grinding the workpiece, any difference between a datum value and the diameter of the particular circumference of the workpiece on which the grinding wheel is acting; means, controlled by the gauging means, for adjusting the position of the grinding wheel in a sense to bring said difference to a predetermined value; a movable datum member providing said datum value; a cam rotation of which is adapted to effect adjustment of the position of said datum member, thereby adjusting the datum value; control means, actuated by the traversing means, and controlling the cam driving means in a manner to relate the rotational position of the cam to the position of the traversing means, the control means being adjustable in a manner to vary the relation between the rotational position of the cam and the position of the traversing means.

The invention relates to grinding machines, and is more particularly, but not exclusively, concerned with grinding machines for grinding accurately to shape and size steel rolls for use, for example, in paper-making processes.

The invention is an improvement on known apparatus for grinding parallel or cambered rolls to a relatively high degree of accuracy. The known apparatus derives the ultimate camber form of a roll from a cam whose profile is cut on a large scale according to the desired law.

In the known apparatus, the cam is rotated by an electrical step by step motion generated by the traverse mechanism of a grinding machine, so that when grinding a roll of the greatest length for which the machine caters, the cam is rotated through its complete working track as the grinding head makes a complete half traverse from the centre to either end of the roll. lf for some reason a roll of greater length were to be ground, a complete half traverse would result in the cam being rotated beyond the end of its working track, with unpredictable results on the camber produced at the extreme ends of the over-length roll.` Where a roll shorter than the maximum is to be ground, there is no alternative but to camber it according to the cam law as generated over a part only of the working track proportional to the length of roll. This working track may for example generate a sine function between limits of 0 and some preferred value Y (usually in the region of 70), and this preferred value is reached at either end of a roll of the designed maximum length. If X/ Y represent the length ratio of any shorter roll compared with the maximum, then if such shorter roll is ground with camber, at either end of the camber form will reach the value given by Xa instead of the preferred value Y".

Ece

There is accordingly in the first place a requirement for a means of ensuring the complete rotation of the camber generating cam during a half traverse of rolls of any length that may have to be ground.

In the second place there is also a requirement to produce at will camber forms (e.g. parabola, ellipse, etc.) according to laws other than that according to which the cam has been cut.

The present invention provides means which may be arranged to meet both these requirements.

According to the invention there is provided a grinding machine comprising: a grinding wheel for grinding a circumferential surface of a workpiece of circular crosssection; traversing means adapted to effect relative longitudinal traversing movement, in the direction of the axis of the workpiece, between the grinding wheel and the workpiece; rotary means for rotating the workpiece while it is being ground; gauging means for determining, while the grinding wheel is grinding the workpiece, any difference between a datum value and the diameter of the particular circumference of the workpiece on which the grinding wheel is acting; means, controlled by the gauging means, for adjusting the position of the grinding wheel in a sense to bring said difference to a predetermined value; a movable datum member providing said datum value; a cam rotation of which is adapted to effect adjustment of the position of said datum member, thereby adjusting the datum value; and control means, actuated by the traversing means, and controlling the cam-driving means in a manner to relate the rotational position of the cam to the position of the traversing means; the control means being adjustable in a manner to vary the relation between the rotational position of the cam and the position of the traversing means.

The control means may comprise: an information carrier; reading means past which the information carrier is moved; and drive means for moving the information carrier past the reading means; the drive means being controlled by said traversing means so as to move in synchronism therewith; and the reading means controlling the cam-driving means in accordance with a predetermined programme carried by the information carrier.

The drive means for the information carrier may comprise a synchro receiver motor driven by a synchrotransmitter which is driven in turn by the traversing means.

The traversing means, synchro transmitter, synchro receiver motor, and information carrier are preferably all driven with a step-by-step motion. For example, the cam-driving means may comprise an electric motor driven with a ste-y-by-step motion by signals imparted to the reading means by the information carrier.

The information carrier may comprise punched tape.

A preferred embodiment of the invention will now be described by way of example and with reference to the accompanying drawings of which:

FIG. 1 is a schematic drawing of the elements of a grinding machine and a control system therefor;

FIG. 2 is an elevation, sectioned in part, of the measuring and reference heads of FIG. l;

FIG. 3 is a circuit diagram of the comparator circuit used with the apparatus of FIG. 1;

FIG. 4 is a circuit diagram of the second and third amplifiers of FIG. l; and

FIG. 5 is a circuit diagram of the first amplifier of FIG. 1.

Also, a further embodiment of the invention will be described with reference to FIGS. 6 to l5 of the accompanying drawings of which:

FIG. `6 shows diagrammatically the elements of a grinding machine and a control system therefor;

FIG. 7 shows somewhat diagrammatically the arrangement of some of the elements shown in FIG. 6, but in greater detail, in a control panel for the system;

FIG. y8 is a theoretical circuit diagram of one of two similar amplifiers in the control system;

FIG. 9 is a theoretical circuit diagram of the input arrangements to one of these amplifiers;

FIG. 10 is a theoretical circuit diagram of the input arrangements to the other amplifier;

FIGS. 11 and 12. show portions of punched paper tape suitable for use as information carriers in the cam control apparatus;

FI'G. 13 is a front view of a tape reader suitable for use in either of the described arrangements;

FfI-G. 14 is a side view of the reader of FIG. 13; and

FIG. 15 is a rear View of the tape reader.

FIG. 1 shows a grinding machine 211 which acts on a workpiece 212 which is rotated about a horizontal axis (by means not shown). The grinding machine comprises a grinding Wheel 213 driven by a direct current electric motor 214 to rotate about an axis parallel to the workpiece axis. The wheel 213 and motor 214 are mounted on a table 215 which is pivotally mounted on a saddle 216. Saddle 216 is continuously traversed along a slide 217 on the frame of the machine by means not shown so that in a normal traverse the saddle will move continuously from one end of the workpiece to the other. A position transmitter 218 carried by the saddle 216 is driven by a pinion 219 which engages with a rack 221 mounted parallel with the slide 217.

Table 215 is pivotally mounted relative to saddle 216i about an axis 222, and the grinding wheel 213 is fed towards and backed away from the workpiece 212 (in a direction perpendicular to the workpiece axis) by pivoting the table 215 about the axis 222. Such pivoting is effected by a wheel feed motor 223 which drives a cam 22.4. Cam 224 bears against one end of a lever 225 which is pivoted on a bracket 226 of the saddle 216, and the other end of which bears against a stop 227 on the table 215. lRotation of cam 224 therefore raises or lowers the side of the table 215 remote from the axis 222 and thereby feeds the grinding wheel 213 towards or backs it away from the workpiece 212.

The diameter of the workpiece 212 is measured on the circumference on which the grinding wheel 2.13 acts, by a gauge comprising an electrically operated measuring head 228, which is carried on a rigid frame (not shown) attached to saddle 216. This rigid frame carries also a micrometer adjustment screw 229l which carries a hardened anvil 231 and which is adjusted in use so that the anvil 231 bears against the lower extremity of the diameter of the workpiece 212 which is measured. A similar anvil 232 bears against the upper extremity of the diameter which is measured, this anvil 232 forming part of the measuring head 228 and being mounted on a shaft 233 to -be capable of radial movement relative to the workpiece.

In a manner to be described with reference to FIG. 2, the measuring head 22.8 gives an output signal at mains frequency, the amplitude of which signal is dependent upon the difference between the position of the anvil 232 and a datum position set by datum set motor 234. The datum is set in accordance with the required diameter of the workpiece, so that the output signal from the measuring head 228 represents the deviation of the actual diameter of the workpiece from the required diameter.

The output from the measuring head 228 is fed over line 235 to a first amplifier 236 where it is amplified to provide an instantaneous indication of the diameter deviation on meter 237 and a permanent record on recorder 238, where an automatic plot of diameter deviation against amount of traverse of the grinding wheel 213 along the workpiece 212 is made. The information regarding the amount of traverse at any moment is fed from the position transmitter 218 to a punched tape 4 digital control apparatus 389 which, in a manner to be described, transmits signals over a line 239 to the drive motor of an apparatus 276 to be described in detail later. Information regarding the amount of traverse is also fed, along the line 239, to a recorder 238.

From the first amplifier 236 the measuring head output signal is taken over line 241 to an input of a second amplifier 242, In this amplifier 242 the diameter deviation is compared with the rate of grinding of the -workpiece 212 by the grinding wheel 213 and the relation between them used to derive an output which controls the speed and direction of the grinding wheel feed motor 223. In this way the rate of grinding is made to vary in accordance with the diameter deviation of the workpiece; a large diameter deviation requiring a high grinding rate and consequently a high grinding wheel feed in and a small diameter deviation meaning that the diameter of the 4workpiece is nearly correct and a low grinding wheel feed in is required to achieve a high accuracy finish.

The rate of grinding of the workpiece 212 by the grinding wheel 213 is measured by measuring the load on the wheel motor 214. This is done by measuring the current taken by the motor 214, part of the driving current being arranged to pass through a shunt resistor (not shown) to give a direct potential signal on line 243 proportional in magnitude to the wheel motor current. This signal is applied to an input of the second amplified 242, and also over line 244 to a wheel load meter 245 which gives an indication of the instantaneous grinding rate.

The output of the second amplifier 242 is applied over line 246 to the input of a motor 247, the speed and direction of which is governed by the amplitude and phase of its input. Motor 247 is mechanically linked to a generator 248, the output of which is applied as negative feedback to an input 249 of the amplifier 242. This negative feed-back ensures the stability of the system and prevents hunting. Motor 247 is also mechanically linked to wheel feed transmitter 251, which generates signals that are transmitted over line 252 to wheel feed motor 223 to drive the motor 223 in a direction determined by and at a speed proportional to, the direction and speed respectively of motor 247, and thereby increase or reduce the grinding rate as necessary. An indication of the instantaneous wheel feed position is given on wheel feed meter 253, a signal for which is derived from a wheel feed position indicator 254 mounted in the drive mechanism for cam 224, the signal being passed over line 255 and amplified in the first amplifier 236.

The apparatus thus far described is arranged to operate the grinding wheel 213 so as to reduce the deviation of the workpiece diameter from a datum set in the measuring head 228. When this deviation is zero no further feedin is applied to the grinding wheel 213 and grinding ceases. The diameter of the workpiece 212 is thus reduced to that corresponding to the datum set inthe measuring head 228. In a manner to be described the datum is set by the datum-set synchro receiver motor 234 which is driven by signals sent over line 256 from a datum transmitter 257. Connected in parallel with the motor 234 is a similar datum-set motor 258 of a reference head 259 which is identical to measuring head 228. This arrangement ensures that the datum value of the reference head 259 changes identically and simultaneously with the datum value of the measuring head 228 in response to signals from transmitter 257. The datum values of the

heads

228 and 259 are set to the required value by mechanically setting the position of the feeler 261 of the reference head 259 to correspond to the desired datum diameter of the workpiece. The output from reference head 259, which is an error signal representing the deviation of the position of feeler 261 from the datum position of datum-set motor 258, is applied over line 260 to a third amplifier 262. The output of amplifier 262 is applied over lines 263a to drive, through motor 263, the datum transmitter 257 and thus the datum set motor 258 (and also motor 234) in such a sense as to cancel the error signal from reference head 259. Therefore the datum value in

motors

258 and 234 are set in accordance with the position of the reference head feeler 261, and will follow any deviations thereof.

In order to grind a workpiece to a cylindrical shape the position of the reference head feeler 261 remains constant at the required value throughout grinding. However, in order to grind a workpiece to a tapered or cambered profile means are provided for varying the desired datum diameter of the workpiece as the grinding wheel traverses the workpiece, by varying the position of the feeler 261 of the reference head 259 in a predetermined manner as the saddle 216 moves along the slide 217. This apparatus is represented at 276 in FIG. 1 and its operation will be more fully described with reference to FIG. 7 showing the alternative arrangement. A set-up meter 299 is connected to the first amplifier 236 to facilitate set-up of the apparatus.

Referring now to FIG. 2, there is shown an elevation, sectioned to the right of line AA, of the measuring head 228 and datum set motor 234. The reference head 259 and its associated motor 258 are identical in construction to head 228 and motor 234 respectively except as described below in respect of

parts

339, 341 and 342. Housing 305 is rigidly mounted at the upper end of a rigid caliper frame (not shown) attached to saddle 216. The caliper frame is adjustable to accommodate various rigid workpieces, but is clamped during a grinding operation. Anvil 232 bears at its lower end on the workpiece at the upper extremity of the diameter which is measured and at its upper end is secured on the end 306 of shaft 233. Shaft 233 is formed integrally with armature 307 of a differential transformer 308. The armature 307 bears a salientl pole 309 which is positioned between two

poles

311, 312 salient upon the stator 313 of the transformer 308. The stator 313 carries two

windings

314, 315 and the armature 307 a single Winding 316. The armature 307 and shaft 233 are suspended from housing 305 by parallel spring strips 233:1 at the ends thereof to permit vertical movement relative to the housing 305 and to the stator 313. A set-up meter 299 is connected to a receiving amplifier 236 to facilitate set-up of the apparatus.

In operation, the two

stator windings

314, 315, which are composed of equal numbers of turns are connected in series opposition and armature winding 316 is energised at mains supply frequency (usually 50 c.p.s.). When the the

stator poles

311, 312, are symmetrically disposed about the armature pole 309 the voltages induced in the

stator windings

314, 315 are exactly balanced and the resultant in the output, which is taken from the series combination of stator windings, is zero. Should the armature 307 then be moved upwards by virtue of the anvil 232 moving upwardly in response to an increase in workpiece diameter, there will be more flux linkage between the armature pole 309 and stator pole 311 than between the armature pole 309 and stator pole 312, the air-

gaps

317, 318, between the poles having been reduced and increased respectively. A resultant voltage will therefore be induced in the output circuit and the sense of the windings is arranged so that this resultant voltage is in phase with the mains supply to the armature winding 316. On the other hand, should the diameter of the workpiece decrease, the anvil 232 will drop and allow armature 307 to drop, the armature 307 being urged downwardly by its weight and by the action of two springs one of which is shown at 319 attached to one end to a pin 321 on the armature and at the other end to a pin 322 on the housing 305.

The output of the differential transformer 308 then gives a resultant voltage in phase or antiphase to the mains supply voltage. In each case the amplitude of the output from the differential transformer 308 Varies in accordance with the degree of deviation of the armature 307, and thus the anvil 232 from the balance condition.

Since the anvil 232 is held in contact with the surface of the workpiece, the armature 307 is effectively fixed in relation to the axis of the workpiece. The output of the differential transformer 308 may therefore be balanced to zero for any workpiece diameter within the range of the stator frame by moving the stator 313 relative to the workpiece 2.12. `In order to alter the datum diameter at which zero output is obtained, provision is made to move the stator 313 relative to the housing 305, which is fixed relative to the workpiece 212. Stator 313 is suspended from housing 305 by further parallel spring strips and is biased downwardly by its Weight in conjunction with the action of two springs, one of which is shown at 323 attached at one end to a pin 324 on the stator and at the other end to a pin 325 on the housing. The stator 3.13 is supported against this bias by a ball 326 on a lever 327. Ball 326 bears against a hardened steel anvil portion 328 of a cross-bar 329 constituting part of the stator structure.

Vertical movement is applied to ball 326 and thence to stator 313 by rotation of the lever 327, which is pivotally mounted in the housing 305 by a pivot pin 331. Rotation of the lever y32'7 is achieved by a horizontal movement Vapplied at the end '332 of the lever 327 fby a micrometer screw 333. Screw 333 is threaded into the housing 305 at 334 and moves horizontally as a result of rotational movement applied to it by a rigidly attached toothed gear wheel 35 which meshes with a lfurther gear wheel 3361. Gear Wheel 336 is driven by Worm gearing in gear-box 337 from the output shaft 338 the datum set motor or receiver 234 (see also FIG. 1), which comprises a stepby-step motor having a three phase field winding connected in delta, with a salient pole rotor. Transmitter 2157 is arranged to commutate a 24 volt alternating supply to any one or any pair of the three field windings of motor 234, in one of two alternative phases, thus giving twelve alternative signals to each one of which corresponds an unambiguous position of the rotor of the motor 234. The twelve rotor positions are arranged to be spaced 30 apart and the transmitter 257 is arranged to give two sets of successive signals corresponding to the twelve positions in each revolution of the input to the transmitter 257. Consequently during one half revolution of the input to the transmitter 257, the receiver receives twelve steps. Rotation of the transmitter 257 input therefore gives a corresponding rotation of the receiver output, but at twice the speed. KIn this way the receiver 234 follows the rotation in one direction or the other of the input drive shaft to transmitter 257. Receiver 258 of the reference head 259 is similarly arranged, and once they have been set to start at zero with the transmitter 257, the two

receivers

234 and 258 remain synchronised with the transmitter and thus with each other.

Activation of the receiver motor 234 rotates the output shaft 338 to raise or allow to drop the stator 313 of the differential transformer 308 and thus change the datum workpiece diameter in the manner described. In the reference head only, there is provided an output from gear-box 337 which drives a Worm 339 which drives a worm-wheel 341. This worm-Wheel 341 has a pointer (not shown) mounted on its shaft 342 to move over a fixed scale (not shown) to give an indication of the instantaneous value of the datum diameter. A disc 343 is mounted on the rotor shaft 33S of the motor 234 of the measuring head only. This disc 343 may Ebe used in conjunction with the datum indicator on the reference head to re-synchronise the positions of the two heads when necessary.

The output signal from measuring head 22'8 is passed through two cathode follower stages of the first amplifier 2.36, it then being applied over line 241 to the input of amplifier 242. The wheel load signal is a direct current slgnal derived `from a shunt resistor in the power circuit (indicated diagrammatically at 214e) to motor 214. The magnitude of the wheel load signal is proportional to the grinding rate and it is applied through line 243 to amplifier 242 to control the magnitude of a signal at mains frequency which opposes the deviation signal from the measuring head 2'28.

FIG. 3 shows the comparator input circuit to amplifier 242. The direct current wheel load signal is passed via line 243 through a saturating winding 351 of a saturable reactor 352. Energising

windings

353, 354 of the reactor are energised from a 24 volt A.C. supply S-S at mains frequency, the energising current passing through

diodes

355, 356 to potentiometer 357 and thence to earth. A biasing flux is applied to the reactor 352' by passing current from a stabilized supply 358 through a biasing winding 359. The voltage from the tap of potentiometer 357 is applied, through a wave shaping circuit 361 to the primary winding 362 of a transformer 363. The other end of winding 362 is connected to the tap of a potentiometer 464, across which is applied over line 249 a velocity feed-back voltage `from generator 2418 (FIG. 1). This feed-back is negative and ensures stability of the system. The secondary 364 of transformer 363 is connected in series in the input line 2'41 for the amplified deviation signal from the measuring head 228. Alternative methods to that described above for deriving an A.\C. signal in proportion to the D.C. grinding wheel load signal may be employed. For example, a system comprising a D.C. galvanometer having a movement which alters the setting of a differential transformer is envisaged.

The relative sense of the

windings

362 and 364 is arranged so that signals from reactor 352 induce in Winding 364 signals which oppose the deviation signals. The extent of the opposition thus provided is determined by the magnitude of the wheel load signal, since the more saturating current there is in winding 351, the more potential is developed across potentiometer 357 and the greater is the magnitude of the opposition signal induced in winding 364.

The error signal 4which is carried by li-ne 365 thus represents the difference between the workpiece diameter deviation and the grinding wheel load. This error signal is applied to an amplifier which controls the wheel feed motor 223, the wheel being fed into the workpiece at a rate dependent upon the amplitude of the error signal. However, feeding in the grinding wheel both increases the load and reduces the diameter of the workpiece. Both these factors tend to reduce the error signal, so that the control system is stable and the grinding wheel eventually assumes a -no-load brushing -position at the datum diameter. A large diameter deviation requires a large grinding wheel load to balance it and reduce the error signal to zero, so that a characteristic of the system is that the rate of grinding automatically Varies in proportion to the deviation of the workpiece diameter from the desired datum.

In addition to the circuit described with reference to FIG. 3 the second amplifier 242 comprises an `amplifier circuit shown in FIG. 4. The error signal from the line 365 is amplified in cascaded

triodes

366, 367, and finally in a push-pull output stage 369. The output from the amplifier is taken from transformer 371 and applied to the control winding of motor 247 (FIG. 1). Motor 247 has a reference Iwinding which is supplied at mains frequency and phase. To obtain maximum power the lcontrol winding must be supplied by a voltage 90 ont of phase with that across the reference winding. The error signal applied to the amplifier input is in phase or antiphase ywith the diameter deviation signal which, as described, is in phase or antiphase with the mains supply. One stage of the required 90 lag is obtained by virtue of capacitor 372 which is connected across `the output of triode 366 to give approximately 30 lag. This lag, together with the inherent lag of the transformer I371 and the remaining amplification stages is adjusted to 90 by a padding capacitor 373 at the input of the amplifier.

Should the input signal to the amplifier be in antiphase to the mains supply, the amplifier output would lead the reference voltage by 90 and the motor 247 would be driven in the reverse direction to back off the grinding wheel from workpiece. This condition would apply if for some reason the measuring head were to register a diameter less than the datum or if the wheel load signal in winding 364 (FIG. 3) were to exceed in magnitude the diameter deviation signal. The back-off condition also applies when relay RL1 is de-energised by a manually'operated off button at the end of a normal traverse or at the end of a partial traverse to remove a large high spot, with the contacts in the positions shown. This makes contact between poi-

nts

2 and 3 and applies a dummy backing off signal from line 374 to the input of the amplifier. Energisation of relay RL1, which is accomplished by operation of a start button on the controller, makes contact between

points

1 and 2 and applies the error signal to the amplifier. Contact is made also between

points

4 and 5, thereby holding relay RL1 on. Contact is broken between

points

6 and 7, and this prevents a second relay RL2 from operating when relay RL1 is energised. Relay RL2 is energised by a microswitch 250 (see FIG. 1) which closes when the grinding wheel is in its fully withdrawn position. On operation, relay RL2, which is a shut-down relay, changes over from the position shown and prevents any operating signal reaching the output of the amplifier and thus the wheel feed motor 223.

The wheel feed motor 223 is a step-by-step servo receiver driven by the commutating transmitter 251 in a manner similar to that described with reference to the servo system comprising transmitter 257 and

receivers

234 and 258 of FIG. 1.

'Ihe remainder of FIG. 4 shows the circuit diagram of the third, datum amplifier 262 (FIG. l). Except that no relays are provided, this amplifier is in every respect the same as the amplifier described above. The input signal is applied over line 260 from reference head 259 :and the output is applied to the control winding of motor 263 to rotate its output shaft in one direction or the other depending upon the phase of the input and at a speed depending upon the magnitude of the input, as is the case with motor 247.

FIG. 5 shows the circuit diagram of the first amplifier 236 of FIG. 1. The output from the

stator windings

314, 315, of the measuring head differential transformer 308 is applied through transformer 375 and cathode follower circuit 376 to the input of a gate 377. Gate 377 is a diode bridge connected as shown with point 378 at a reference voltage. The gate limits the range of the input to cathode follower 379 to between two reference values. In operation the potentiometer 381 is adjusted so that a signal equivalent to a diameter deviation of .001 inch above the datum just fills the gate 377.

The output from cathode follower 379 varies in accordance with the output from differential transformer 308 between zero and a maximum value governed by gate 377, and appears across a potentiometer 382, the tap of which is connected through a primary winding 383 of a transformer 384 to a tap of a potentiometer 385. The output of the circuit is taken from the secondary winding 386 of transformer 384 and constitutes the diameter deviation signal which is applied to the comparator circuit of F IG. 3.

Potentiometer 382 provides that the diameter deviation signal does not exceed a predetermined maximum value which is a predetermined proportion of the maximum output from cathode follower 379. This maximum rvalue corresponds to a maximum permissible grinding wheel motor load current. Thus the arrangement is such that the control system cannot, however large the out of balance signal from the measuring head, cause an increase of the grinding wheel motor load current to beyond the permissible maximum. The maximum wheel load potentiometer 382 is set empirically.

An alternating reference voltage is applied across potentiometer 385 in antiphase with the voltage across potentiometer 382. This ensures that when the diameter deviation signal from the measuring head is zero, indicating that the desired datum diameter has bee-n reached, a small apparent diameter deviation signal will still be applied to the comparator circuit. This small signal is arranged, by empirical adjustment of the minimum wheel load potentiometer 385, to be of amplitude just sufiicient to balance the no-load current taken by the grinding wheel motor when the grinding Wheel is merely brushing, but not grinding, the work-piece. In this way a balance is obtained at the datum diameter with the grinding wheel brushing the workpiece, no error signal being given by the comparator circuit of FIG. 3-

A further embodiment of the invention, differing principally from that described above in the type of measuring and reference heads employed will now be described with reference to FIGS. 6 to 10.

In this embodiment, a grinding machine 11 acts on a workpiece 12 which is rotated about a horizontal axis (by means not shown). The grinding machine comprises a grinding wheel 13 driven by an electric motor 14 to rotate about an axis parallel to the workpiece axis. The wheel 13 and motor 14 are mounted on a cross-slide 15 which is fed towards and backed away from the workpiece 12 (in a direction perpendicular to the workpiece axis) by feed-mechanism 16 which includes a motor 42 driving a cam 16a and a rocking lever 1Gb. The cross-slide is carried on a saddle 17 which is continuously traversed along the workpiece (by means not shown) along a slideway 20.

A pneumatic measuring head 18 is mounted at the top of a rigid frame 19 rigidly connected to the saddle 17. From the bottom end of this frame projects an anvil 21 which bears against one end of a diameter of the rotating workpiece in the plane of that particular circumference on which the grinding wheel 13 acts, whilst the feeler 22 of the measuring head 18 bears against the opposite end of the same diameter. Air is supplied at a standard pressure of 3% pounds per square inch by air supply unit 23 through

air lines

24, 25 and 26. Air line 24 feeds air to the measuring head 18, and changes of diameter of the workpiece move the feeler 22 axially, which alters the drop in pressure across an orifice in the head 18. The resultant modified air pressure is a measure of the diameter of the workpiece with respect to the datum diameter corresponding to the position of the orifice, and this pressure is transmitted through an air line 27 to pressure comparison apparatus 28. This apparatus compares the modified pressure in the air line 27 (giving a measure of the workpiece diameter deviation) with the standard pressure in air line 25 by means of a pair of differential bellows 29, 31 to which air at standard pressure and modified pressure is supplied, respectively. The resultant mechanical movement of the bellows as the modified air pressure changes is converted (by means 32 including a differential transformer 36-see FIG. 9) into a varying electrical signal which is fed into the grinding machine control amplifier 33. A similar pair of

differential bellows

29a, 31a operate a pressure gauge 34 which indicates on its dial the deviation in the workpiece diameter i.e. the difference between its actual diameter and the predetermined datum diameter.

The rate of grinding of the workpiece 12 by the grinding wheel 13 is measured by measuring the load on the wheel motor 14, which in this case is an alternating current motor. The current taken by the motor 14 is arranged to pass through the primary winding 35d of a transformer 35, the secondary winding 3517 of which provides an alternating voltage signal at mains frequency proportional to the wheel motor current,

The various signals are fed into an input network, the circuit diagram of which is shown in FIG. 9. This input network is incorporated with an amplifier, the circuit diagram of which is shown in FIG. 8, to form the grinding machine control amplifier 33.

The input network shown in FIG. 9 includes resistors R1-R7,

variable potentiometers

38, 41, 43 and 45, capacitors C1-C4, transformers 36 and T1, and a self-latching relay 46 with

operating buttons

47 and 48 and coil L1.

The remainder of the circuit of the amplifier 33 is shown in FIG. 8 and includes thermionic valves VlA, V1B and V2 of type ECC81 and V3 and V4 of type EL90, resistors R8-R21, variable potentiometer 44, capacitors CS-Clfl, transformer T2, and inductance L2.

Referring now to FIG. 9, an A.C. signal of 6 volts at mains frequency is fed in at the terminals A-A, and through a resistance network 37 including a potentiometer 38. A voltage tapped off across the potentiometer 38 is applied to the primary winding 39 of differential transformer 36 similar to transformer 308 previously described, of the converting means 32. The armature of transformer 36 is coupled to the

bellows

29, 31 so that as the latter move, an output signal representing the diameter deviation is obtained.

The alternating voltage from the transformer 35 representing the grinding motor load is injected into the input network at terminals B-B and through transformer T1. A further signal at mains frequency is applied to the terminals C-C in order to cancel out that part of the motor load signal which represents the no-load condition of the grinding wheel, so that the resultant signal represents the mechanical load on the grinding wheel 13. By altering the potentiometer 41, the no-load cancelling signal may be adjusted to an experimentally determined correct value.

A further signal is applied, in opposition to the load signal, at terminals D-D of the input network which are connected to the terminals DD-DD at the output end of the grinding machine control amplifier (see FIG. 8). This signal represents the velocity with which the grinding wheel 13 is fed into or backed off from the workpiece by the motor 42 of the feed mechanism 16. The negative feed back thus provided overcomes inertia effects in the system and checks any tendency to hunt about the no signal, position. The signals derived from inputs at terminals C-C and D-D may both be adjusted by means of potentiometer 43 in the input network, whilst the feed back to input at D-D may also be adjusted by potentiometer 44 (see FIG. 8). The

potentiometers

38 and 41 control respectively the maximum and minimum grinding wheel loads which are permitted by the control system, and are provided with calibrated control knobs 109 and 1.11 respectively (FIG. 7).

An over-riding manual control for controlling motor 42 to back-off (i.e. withdraw) the grinding wheel from the workpiece is provided in the input network. For this purpose a mains frequency voltage of 6.3 volts is applied to terminals H--H and through an adjustable potentiometer 45 in such a way that, when the resultant voltage appearing at the terminal F is applied to the grid of the second stage of the amplifier 33, the amplifier controls the motor 42 to back-off the grinding wheel. A conventional self-latching relay 46 is employed, powered by 300 volts D.C. When the button is pressed, contacts 49 are held closed, connecting the point F to the point G on the amplier 33 (see FIG. 8), until the button 48 is pushed. The output of the input network at terminal JJ is fed into the main amplifier at terminal J.

Referring again to FIG. 6, the output of the grinding machine control amplifier 33 drives a motor 51, which is mechanically coupled to a synchro transmitter 52. This transmitter drives the motor 42 which feeds and backs off the grinding wheel 13 to or from the workpiece. The controls of the input network and the main grinding machine control amplifier are set so that, when button 48 has been pressed the amplifier controls the motor 42 so that it feeds or backs-off the grinder wheel so that the rate of grinding varies with the deviation of the workpiece diameter from the predetermined datum diameter. When the button 47 is depressed, the relay coil L1 is energised The desired datum diameter for the workpiece is altered Y by adjusting the pneumatic workpiece measuring head 18. As the position of the aforesaid orifice within the head is altered along the direction of movement of the plug connected to the feeler 22, so the zero or datum position, with respect to which the head measures the diameter deviation of the workpiece moves. The orifice of the head 18 is moved by a zero-set synchro receiver motor 61 driven by a transmitter 62. Connected in parallel with the motor 61 is a similar zero-set motor ,63 so that the latter adjusts the zero-position of pneumatic reference head `64 identically and simultaneously with the zero-position of the measuring head 18 adjusted by the motor 61. Thus the zero-positions of the measuring head 18 and the reference head 64 are always the same. The zero-positions of the heads are set to the required positions by setting mechanically the position of the feeler 65 of the reference head 64 to correspond to the -desired datum diameter of the workpiece, and arranging that the air-pressure output signal from the reference head controls the zero-set transmitter 62 to set the zero-positions of both heads so that the reference head shows no difference between its zero position and the measured position of its feeler 65. Thus the zero-position of the measuring head 18 is continually adjusted to correspond to the desired datum diameter set by the position of feeler 65 of reference head 64.

The means for enabling the output signal from the reference head to control the transmitter 62 are generally similar to those described above which enable the signal from measuring head 18 to control transmitter 52. The air pressure signal from the reference head 64 is fed into a pressure comparison apparatus 66 similar to the apparatus 28, and including differential bellows 67, 68 into which the standard pressure from air-line 25, and the modified pressure from air-line 26 (i.e. the air pressure signal from head 464), are introduced respectively. The resultant mechanical movement of the bellows as the modified air pressure changes is converted into a varying electrical signal by means y69 (similar to means 32) which includes a differential transformer 71.

This varying electrical signal is fed into a zero-set control amplifier 72 which incorporates an input network circuit diagram which is shown in FIG. This input network includes the differential transformer 71, a variable potentiometer 75, and a capacitor C11. The circuit diagram of the remainder of the amplifier 72 is shown in FIG. 3, the

amplifiers

33 and 72 differing only in their input networks. The terminal JJ] of this input network is connected to the terminal I 0f the main amplifier 72. The armature of the differential transformer 71 is moved by bellows 67 and 68 with respect to its primary and secondary windings, thus altering the voltage induced in the secondary windings due to an alternating voltage of 6 volts applied to the primary winding 73 at terminals AA-AA. A further signal is applied at the terminals DDD-DDD of the input network, which are connected to the terminals D-D at the output end of the zerset amplifier 72. This signal represents the rate of rotation of the motor 74 which the amplifier controls. The negative feed-back thus applied to the amplifier 72 ensures stability of the system. The amount of feed-back may be adjusted by means o-f the potentiometer 44 in the output end of the amplifier 72, and by means of the potentiometer 75 in its input network. The output of the zero-set amplifier 72 drives a motor 74 which is mechanically coupled to the synchro transmitter 62. The transmitter 62 drives the zero-set

motors

61 and 63 as aforesaid.

In order to grind workpieces with tapered or cambered profiles, means are provided for varying the desired datum diameter of the workpiece as the grinding wheel traverses the workpiece, by varying the position of the feeler 65 of the reference head 64 in a predetermined manner as the grinding wheel moves along the slideway This apparatus is represented conventionally at 76 in FIG. 6 and is shown diagrammatically in greater detail in FIG. 7. This apparatus is exactly the same as that indicated at 276 in FIG. 1, where feeler 261 of the reference head 264 corresponds to feeler of reference head 64. The description of the apparatus at 76 applies equally to both embodiments.

The end of the reference head feeler l65 rests on a cross arm 7-6, near one of its ends 77 at which it is slung resiliently on a spring strip` 83. At its other end 78 the arm is urged downwardly by a spring 79 and is adjustably supported by a fiexible steel tape 81 wound around and attached to a datum set spindle 82. Resiliently attached to the end 77 of the cross arm by a spring strip 86 is the lower end of a pick off ar-m I84, which is supported by a spring 85, providing support for the weight of

arms

84 and 76, together with the reaction of the feeler 65. The arm 84 is provided at `itsirpper end with a roller 87 and can pivot about its lower end on the spring strip 86, the roller 87 moving along the underside of a cam follower arm 88 which is pivoted at one end 91. Near its uper end the arm V84 is attached to one end of a spring 89 which tends to move its upper end away from the pivot 91, and is adjustably retained in a substantially upright position by a flexible steel tape 92 which is wound around and attached to set percentage camber spindle 93. The end of the cam follower arm 88 remote from its pivot 91 is provided with a roller 94 which bears on the periphery of a cam 95. The roller is urged into contact with the cam by a. spring 96 attached to the shaft near the roller.

It will be apparent that as the cam rotates, the cam follower arm 88 will rotate to a certain extent about its fixed pivot 91. The roller 87 is in contact with the arm 88 at some point near its pivot 91, so that the arm 84 is moved in a direction more or less along its own length, by or against the urging of its supporting spring 85. The proportion of the motion of the cam follower roller 94 transverse to its arm 88 which is imparted to the arm 84 as longitudinal motion depends upon the relative distance of the rollers 94 and 87 from the pivot 91 i.e. upon the position of the roller 87 along the cam follower arm 88. This variable position is set by rotating the set percentage camber spindle 93 so that the flexible tape 92 restrains the arm 84 in the desired transverse position against the urging of the spring 89. The longitudinal position of the arm 84 is transmitted to the end 77 of the cross arm 76 as motion of that end transverse to the arm 76, the spring strip 83 allowing such motion The transverse position of the other end 78 of the cross arm is determined by the angular position of the datum set spindle 82, which controls the length of the tape 81 which extends from the spindle transversely of the arm 84 to support the end 78 against the urging of spring 79.

Thus the longitudinal position of the feeler 65 of the reference head 64 depends upon (a) the angular position of the datum set spindle 82 and (b) the longitudinal position of the pick off arm 84. The last-mentioned position further depends upon (c) the angular position of the set percentage camber spindle 93 and (d) the angular position of the cam 95.

The cam 95 is rotated through gearing 102 by a synchro receiver motor 97, which is driven by signals from a punched tape digital control apparatus, indicated diagrammatically at 390, the operation of which will be described in detail below. The control apparatus is driven by signals from a synchro transmitter 98 mounted on the grinding machine saddle 17. A pinion wheel 99 is mounted on the shaft of the transmitter 98 and engages with a rack 101 fixed relative to the slideway 20. As the saddle is traversed along the slideway 20, the shaft of the transmitter 98 is rotated by an angular amount proportional to the saddle travel. Thus the cam 95 is rotated automatically, as the grinder wheel 13 traverses the workpiece, in a manner depending on programme employed on the punched tape used in the control apparatus 390. The shape of the cam 95 is such that the changes of position of the feeler 65 of the reference head, as the cam 95 rotates, produces the desired change of desired datum diameter, and thus causes the grinder to grind the workpiece 12 to the desired cambered profile. The camber produced is determined by the control apparatus, as will be described below, but may be reduced proportionately by setting the angular position of the set percentage camber spindle 93 so that the roller 87 is nearer to the pivot 91, a calibrated scale being provided for that purpose. In particular, when the roller 87 is opposite the pivot 91, the arm 84 will remain stationary as the cam revolves, and no camber will be produced on the workpiece 12. The initial datum diameter for the workpiece is set by adjusting the angular position of the datum set spindle 82. Further a reversing switch 103 is provided to reverse the sense of rotation of the motor 97 with respect to that of the transmitter 98, so that increasing and decreasing cambers may be ground along the length of the same workpiece 12 with the same cam 95 whilst the saddle 17 is traversing in the same direction. Reference to FIG. 1 shows a corresponding switch 220', mounted on the saddle 216, which may be operated by contact with a striker 220a when the saddle is in an appropriate traverse position with respect to the workpiece. If a symmetrically cambered roll is required, e.g. one which tapers at its ends, the switch 220 is arranged to be operated when the grinding wheel is at the centre of the workpiece. Cam 95 is arranged to rotate to its full extent for half the traverse length. At the half-way point, switch 220 changes the relative sense of rotation of the cam 95 with direction of movement of the saddle. The cam, having rotated to its full extent then reverses in direction of rotation and ensures a symmetrically ground workpiece, the same cam having been used for both halves of the workpiece.

In order to provide a permanent record of the variation of the diameter of the workpiece along its length, there is provided a conventional chart recorder 104 (conveniently mounted on the cabinet of the air supply unit 23). The recording pen 105 of the recorder moves under the control of a diameter deviation indicator (not shown) similar to the one 34 already described, and the rotation of the chart is produced by a motor (not shown) driven by the synchro transmitter 98, so that angular rotation of the chart corresponds to traversing of the measuring head 18 along the workpiece.

There is also provided an indicator 106 driven by a receiver motor 107 which is electrically coupled to the transmitter 52 to indicate continuously how far the grinding wheel is fed towards the workpiece. An ammeter 108 is provided, to indicate the current passing through the grinding wheel motor 14. An indicator 112, driven by the zero-set motor 63 of the reference head 64, gives a continuous indication of the instantaneous value of the predetermined datum diameter.

The method of operating the machine is as follows. A blank oversized workpiece is mounted in the grinding machine. The datum set spindle `82 is set to obtain an indication of zero diameter deviation at the desired diameter of the finished workpiece. If a plain i.e. uncambered roll is required, the set percentage camber spindle 93 is set to indicate zero percent, i.e. the roller 89 is at the pivot point 91. If a cambered roll is required, a cam 95 having a suitable profile is selected, and the set percentage camber spindle 93 is set to indicate the desired percentage (calculated from the total camber produced when 100% camber is set). 'Ihe switch 103 is used for synchronising the cam zero with the appropriate traverse position.

The various pre-set controls in the

ampliers

33 and 72 or 236 and 242 are set to give the control system the required characteristics.

The maximum and minimum

wheel load potentiometers

38 and 41 are set to the required values. For example, the maximum wheel load potentiometer 38 may be set so that the ampliiier allows the full load on the grinding wheel to be applied for a deviation in the diameter of the workpiece of .001 inch or more. The minimum wheel load potentiometer 41 may be set so that the ampliiier allows 5% of the full load to be applied for zero deviation.

The workpiece 12 is set in rotation and the automatic control system switched in to ensure, in the manner described, that the rate of grinding decreases as the workpiece 12 diameter approaches the desired dimension. The grinding wheel 13 is traversed along the workpiece 12 at a rate which is slow enough for the above-mentioned relationship to be maintained by the control system, whether the desired datum diameter is constant (for a plain roll) or varies (for a cambered roll). In the latter case, the datum diameter is automatically varied by the cam and its associated mechanism, as previously described. In order that a roll may be produced having a double camber, i.e. a roll which is thicker at its centre and decreases in diameter towards its ends, the camber

motor reversing switch

103 or 220 enables the same cam 95 to generate the two cambers in different directions, the saddle 17 moving in the same direction, and the transmitter 98 rotating in the same direction, during the cutting of Iboth cambers. The

switch

103 or 220 is positioned on the grinding machine so that it is automatically operated at the correct point in the traverse as the saddle 17 passes it.

The general construction and operation of the machine now having been described there will now be described the manner of operation of the punched tape digital control `apparatus indicated at 389 in FIGS. l to 5 and 390 in FIGS. 6 to 10. Reference will be made only to the embodiment of FIGS. 6 to 10 and it will be understood that the control apparatus 389 in the embodiment of FIGS. 1 to 5 operates in a similar manner to the control apparatus 390.

The control apparatus 390 is digital in character, the digits concerned being the steps in a step-by-step programme recorded on punched paper tape, so that any programme is indefinitely repeatable within the limits of accuracy set by a single digit. Such limit can readily be made negligible. The control apparatus satisfies two main requirements. Firstly, by employing a suitable punched tape the time taken for the cam 95 to perform one revolution may be matched to the time taken for the grinding wheel 13 to be traversed the -full length of the workpiece, since this latter time will, of course, vary according to the length of the workpiece. Secondly there is a requirement to produce at 'will camber forms (eg. para'bola, ellipse etc.) according to laws other than that to which the cam 95 has been cut. This can be achieved by employing a suitable programme on the punched tape to vary the cam profile by varying the rate of rotation of the cam 95 as it rotates.

In the control apparatus 390 the punched paper tape is fed forward and backward through a reading machine, in step with the traversing head of the grinding machine. A separate tape is required for every roll length for which a complete rotation of the cam 95 is desired, and the length of any tape will ybe proportional to the length of its corresponding roll. The tape will carry a pattern of punched holes, Iwhich as they pass through the reading machine will generate the standard succession of step by step signals for driving motor 97 of the camber cam 95. By rst generating more signals than are required for complete rotation of the cam 95, onward stepping sign-als may be interspersed with standstill signals to produce a cam movement that bears any required relation to the traverse movement of the grinder Wheel 13.

As mentioned abo-ve the traverse position step by step transmitter 98 drives the paper tape through a reading head 'by a sprocket such that the tape is positively driven, and will be moved back and forth, one step at a time, by the traverse transmitter signals. The step movement of the tape is such as to laccommodate a row of six punched holes across its width, and typical arrangements are shown in FIGS. 11 and 12. Of the six positions, either two or three are punched at any station, and twelve of the possible arrangements of such holes in the six available positions can be used to generate the twelve characteristic and successive step lby step switching patterns. While the following more detailed description gives in the simplest terms an elementary working system, any of the commonly available paper tape systems of a more sophisticated character, and better suited to computer punching, may be employed.

lLet the maximum roll half length be R", and the minimum half length requirement be r. Let the total number of step by step signals now .generated by the traverse in traversing a distance R be N. Then the number of step by step signals to give full rotation of the camber cam will also be N.

The traverse transmitter is geared to deliver R/rXN step -by step signals in the course of a traverse of R", and these signals are used to step forward the paper tape. In the course of NR/ r steps of the tape, the cam 95 receives N steps only, equally spaced, or with an irregularity not exceeding one step about the mean. NR/ r-N steps of the tape must produce no steps of the cam. Following any step by step signal punched in the tape, in the sequence 1-12 shown in FIG. l1, there must be R/ r-l repetitions of the same signal before a change is made to the next signal pattern of the sequence, which is again to be followed by the same number of repetitions before the next change. This instruction holds for any value of r, say r', between r and R. It is clear that the value of R/ r--1 is unlikely to be a whole number, and if it is not, then the whole number above or lbelow the nearest whole number must be alternated with it in a calculated pattern so that over a complete traverse the difference between the number of required and actu-al cam step signals does not exceed one at any time. Such a programme will allow a half traverse of r, yielding NRr/ r steps to deliver N steps to the cam and thus produce a complete rotation at la rate very closely tied to the traverse rate.

To meet the requirement of providing for different camber laws while using the same cam, it is necessary to note the cambers yielded by the cam at points along the traverse. It is then necessary to calculate the different points along the traverse at which these cambers are required under the new law. This creates a demand for a particular camber to be reached earlier at one point and later at another than would be reached by uniform rotation of the cam 95. With a programme tape running synchronously with the traverse, |with a greater rate of stepping than is needed to complete the cam rotation, it merely ybecomes a matter of omitting occasional scheduled repeat punchings to bring the cam forward more quickly,

or to introduce additional intermittent duplications of punch pattern, so that the cam rotation is held back, thus decreasing the rate of camber. If such a modied camber track is to be laid out, as it clearly can be, within an error limit of a single step, a computer is a necessity for its preparation.

A suitable form of tape reader is shown in FIGS. 13, 14 and 15. The tape reader comprises a step by step motor 391 mounted on a support 392. The motor 391 drives a gear wheel 393 which in turn drives an idler wheel 394. The idler wheel 394 drives directly gear wheels 395 which rotate tape driving sprocket wheels 396 mounted on the .opposite side of the support.

Co-axial with the idler wheel 394 are co-axial sprocket wheels 397 which drive further sprockets 398 through endless chains 399. Co-axial with the sprockets 398 and connected to them through free wheel and slipping clutch assemblies are tape spools 400.

Punched paper tape extends from one spool 400 to the other across the sprocket wheels 396 and, as best lseen in FIG. 13, between the sprocket wheels 396 the punched tape passes over a fixed support 401. A cavity 402 vis formed in this support 401 and extends4 across the full width of the paper tape. The cavity is covered by a window 403 and disposed within the cavity, yspacedy across the width of thepaper tape, are seven photo diodes, photo transistors, generating cells or similar light sensitive devices. The devices are so disposed that each underlies one row of punched holes in the paper tape.

A lamp 404 is mounted on the support 392 and light from the lamp is reflected downwardly on to the light sensitive devices by means of a prism 405. A window 406 is provided in the support 392 between the lamp 404 and the prism 405.

There are twenty four tape engaging tags on each sprocket wheel 396 and these engage a continuous line o f perforations 407 (see FIGS. 11 and 12) whichextend along a part of the tape not used for signal perforations.

The step by step motor 391 rotates at twenty four steps per revolution and each step of the motor will carry the tape forward (or backward) according to the succession of step by step signals received by it from the transmitter 98. The distance moved by the tape at each step will be slightly more than is needed for a transverse row of holes that are punched in the tape to generate coded signals. Any holes punched inthe tape must always lie above one or more of the light sensitive devices in the cavity 402. Light is able to reach a light sensitive device freely only when a punched hole lies over the device. Each light sensitive device is arranged in known manner, with or Without an associated amplifier, to energise a relay to close a pair of contacts. The seven light sensitive devices and their associated seven relay contacts form a complete step by step transmission system, and the system will provide the three field terminals of the step by step receiving motor 97 with energisation for step by step rotation in a manner determined by the programme punched on the tape.

The tape punch pattern at each step is always one of the arrangements numbered 1-12 in FIG. 11 and if any pattern repeats itself in successive steps, the receiving motor 97 will remain stationary. If the pattern changes, it must change only to the next higher or lower numbered pattern in the 1-12 sequence according as the desired motor rotation is in one direction or the other. The next step beneath 1 is of course 12, and the next step above -12`is -1.

A separate tape is run off by computer for cambered Workpieces of different length, and/or, for each"differ ent camber law. It might Well be considered that a particular tape belonging to a roll of certain length would be perfectly suitable for use on another roll only slightly shorter. In practice there is a distortion of the camber law through failure to complete the rotation of the cam.

Many commercial computers are equipped with a device for punching paper tape as a means of temporarily or permanently recording particular computations. `It is envisaged that such a computer could, be ,employed to prepare paper tapes for control of the grinding machine.

A tape required to :grind a workpiece of half length r, where the grinder traverse transmitter generates-step by step signals at a rate of S steps per inch of traverse, must have a total of Sr punch positions, and this determines the length of tape. If the cam requires N steps to rotate through its full working profile, then Sr punch positions in the tape must yield N step transmissions to the camber cam drive. To produce such a tape, the computer isV programmed to punch out the pattern 1-12 of FIG. 1-1 repetitively N/ l2 times, spread as uniformly as possible over Sr punch positions, the gaps being lled in by repetition of the immediately preceding signal pattern.

T o produce a tape which will cause the grinder control to generate a camber law other than that generated by rotating the cam in synchronism With the grinding traverse, it is necessary to set up in the computer memory a mathematical formula from which the computer can derive the desired camber coordinate for each of the Sr steps along the tape. Into another memory of the computer is placed the formula for the cam used in the grinder control. The computer is then programmed to punch out a tape containing Sr punch positions, again giving N/l2 repetitive sequences of the pattern 1-12 of FIG. 11.

At each step of the tape, the computer compares the desired camber with the camber produced by the cam. If the camber produced by the cam is equal to or greater than the desired camber, any existing step by step transmission is maintained by repetition of the punch pattern. When the camber produced by the cam is found to be less than the desired camber, then the punch pattern changes at the rst opportunity. Thus the desired camber is matched by the advanced or delayed positioning of the cam, within a limit of a single step.

The tapes may be stored and operated in cassettes of the kind commonly used for amateur cine film. These would be placed in the tape reading machine so that an exposed and marked part of the tape provides a reference point, which is linked to the centre or end of the workpiece where a tape reversal will normally take place. The tape drive sprocket system engages with the tape at this point and remains engaged until the cassette is nally removed at the completion of the grind. This removal is done once more at the centre or end of the workpiece, so that the marked point of engagement is visible.

As the tape is driven forward by the sprocket drive, the tape that has passed through the reading head is coiled up in the reel-up sprocket of the cassette, by a lightly engaged friction drive. The unread tape is drawn from the un-reel pocket on the opposite side, and the reeling mechanism is allowed to free-wheel. When the sprocket drive is reversed as the grinding machine traverse is reversed or as the centre line of the roll is crossed, so the tape direction is reversed, and the driving arrangements to the reel-off and reel-up cassette pockets are reversed.

I claim:

1. A grinding machine comprising:

(a) a grinding wheel for grinding a circumferential surface of a workpiece of circular cross-section;

(b) traversing means adapted to effect relative longitudinal traversing movement, in the direction of the axis of the workpiece, between the grinding wheel and the workpiece;

(c) rotary means for rotating the workpiece while it is being ground;

(d) gauging means for determining, while the grinding wheel is grinding the workpiece, any difference between a datum value and the diameter of the particular circumference of the workpiece on which the grinding wheel is acting;

(e) means, controlled by the gauging means, for adjusting the position of the grinding wheel in a sense to bring said difference to a predetermined value;

(f) a movable datum member providing said datum value;

(g) a cam rotation of which is adapted to effect ad justment of the position of said datum member, thereby adjusting the datum value;

(h) control means, actuated by the traversing means, and controlling the cam-driving means in a manner to relate the rotational position of the cam to the position of the traversing means;

(i) the control means being adjustable in a manner to vary the relation between the rotational position of the cam and the position of the traversing means.

2. A grinding machine according to claim 1 wherein the control means comprise:

(j) an information carrier;

(k) reading means past which the information carrier is moved;

(1) drive means for moving the information carrier past the reading means;

(In) the drive means/ being controlled lby said `traversing means so as to move in synchronism therewith;

(n) the reading means controlling the cam-driving means in accordance with a predetermined programme carried by the information carrier.

3. A grinding machine according to claim 2 wherein the drive means for the information carrier comprises a synchro receiver motor driven by a synchro transmitter which is driven in turn by the traversing means.

4. A grinding machine according to claim 3 wherein the traversing means, synchro transmitter, synchro receiver motor, and information carrier are all driven 'with a step-by-step motion.

5. A grinding machine according to claim 4 wherein the cam-driving means comprise an electric motor driven with a step-by-step motion by signals imparted to the reading means by the information carrier.

6. A grinding machine according `to claim S wherein the information carrier comprises punched tape.

References Cited UNITED STATES PATENTS 3,088,250 5/1963 Hold et al. 51-165 3,321,869 5/1967 Parrella et al 51-49X 3,391,497 7/1968 Parrella et al. 51-165 LESTER M. SWINGLE, Primary Examiner U.S. Cl. X.R. 51-165 i