US2984952A - Pressure operated feed control for grinding machines - Google Patents

Description

y 3, 1961 K. M. GEBEL 2,984,952

PRESSURE OPERATED FEED CONTROL FOR GRINDING MACHINES Filed April 29, 1958 2 Sheets-Sheet 1 FIG. 2.

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LU 3 www Z, INVENTOR ATTORNEYS May 23, 1961 K. M. GEBEL 2,984,952

PRESSURE OPERATED FEED CONTROL FOR GRINDING MACHINES Filed April 29, 1958 2 Sheets-Sheet 2 FIG. 4.

INVENTOR ATTORNEYS United States Patent,

PRESSURE OPERATED FEED CONTROL FOR GRINDING MACHINES Kurt M. Gebel, Waynesboro, Pa., assignor to Landis Tool Company, Waynesboro, Pa., a corporation of Pennsylvania Filed Apr. 29, 1958, Ser. No. 731,681

7 Claims. (Cl. 51-165) The following specification relates to an improved method for the speed control for grinding wheels and a pressure operated speed control for grinding wheels. It is applicable to grinding wheels which are advanced into contact with a rotating workpiece upon which successive grinding operations are to be performed. This requires variation in the speed at which the grinding wheel is advanced.

In advancing a grinding wheel toward a workpiece there is an unavoidable period during which the grinding wheel is approaching the Work without actually being in contact with it or performing successful work. This is lost time which it is desirable to avoid.

When the wheel first contacts the rough workpiece, there is a preliminary period during which rough grinding can be accomplished on the projecting parts of the workpiece and before the wheel maintains continuous contact. Following this the grinding wheel is advanced for grinding at a relatively slow rate of speed.

Finally the speed of the grinding Wheel advance must be reduced in order to accomplish the final grinding which results in completion of the grinding work.

One of the objects of this invention is to shorten the time required for each grinding cycle by minimizing the period during which the grinding wheel rotates out of contact with the workpiece.

A further object of the invention is to select the desirable fast speed and subsequent slow speed of the grinding wheel advance depending upon the load upon the latter.

A still further object of the invention is to provide for changing the speed of the wheel advance as it approaches the work by stopping the rapid speed and at the same time applying an intermediate speed through the normally slow speed mechanism.

A still further object of the invention is to provide for cycling the operation by means of a meter relay and solenoid which are operated by a relay responsive to the motor circuit of the grinding wheel.

Among the objects of the invention is to provide means by which the change in speed is made dependent upon the completion of the movement of the rapid feed mechanism wheel base to its most advanced position.

An incidental purpose of the invention is to delay actuation of the change in speed until predetermined increase in load occurs after the normally sudden increase in load resulting from first contact by the wheel upon the work.

One of the objects of the invention is also to provide a blocking valve which will delay the slow feed until the stroke of the rapid feed has been completed, this valve being operated by the exhaust pressure from the rapid feed during advance, and by the retracting pressure during retraction of the wheel feeding means.

As illustrating the essential features of this invention I have shown the preferred form by way of example on the accompanying drawings in which:

Patented May 23, 1961 Fig. 1 is a side elevation of a grinding wheel and a workpiece;

Fig. 2 is a diagrammatic view of the means for advancing and retracting the grinding wheel;

Fig. 3 is a graph showing rates of grinding and timing and Fig. 4 is the wiring diagram utilized.

In brief the invention comprises utilizing the driving circuit for the grinding wheel motor for the purpose of actuating a relay which in turn controls the feed selection and sets into motion the change in speeds from the initial high feed to an intermediate feed, and ultimately a slow feed followed by retraction.

On the drawings the workpiece 11 consists of a cylindrical object which is held between centers 12 and driven by conventional means, not illustrated.

The operating means for the grinding Wheel includes lubricating pressure and this will actuate a bellows 13 01' similar pressure responsive device. When the bellows 13 is expanded, it closes a switch 14 in the line circuit.

A grinding wheel 15 is mounted with its wheel shaft 16, driven by motor 17. The grinding wheel and its motor are mounted upon a base 18 by which limited advance and retraction relative to the workpiece 11 is carried out.

Power is supplied in the form of three-phase alternating current through the leads L1, L2, and L3, indicated on the drawings at 19.

A relay 20 is provided for connecting the power to the wheel drive motor 17. This relay has a contact 21 connected to L1 and to the motor. A similar return contact 22 connects the motor to line wire L2.

An independent circuit portion with line wire L3 extends through contact 23 of the relay 20 and to a trans former 24. Transformer 24 in turn is connected by lead 25 to the drive motor circuit and thence returning to L2.

Contacts 21, 22 and 23 are normally open except when closed by the circuit through the switch 14.

A load relay 26 is connected through its normally closed contact through switch 14.

A feed selector valve 27 is provided for selecting and controlling the fluid pressure means which operates the rapid feed and the slow feed. This valve 27 is connected to the power line through a current relay 28.

The relay 28 receives current from the load relay 26 and returned to line L2. There are two contacts 29 and 30 for the current relay 28. These are normally open and are connected on one side to a solenoid 31 forming part of the feed selector valve 27. Current through contact 29 is supplied from line L1, while the return to L2 is through contact 30.

It will be apparent that current from L1 passing through switch 14 travels in one direction through the drive motor relay 20 and in another branch through the normally closed contact of the load relay 26, thence through the coil of relay 28 in its return to L2.

Current from the pressure switch 14 is delivered to a time relay 32. The other side of relay 32 is connected to line L2. The time relay 32 has a normally open contact 33. The relay is so designed as to protect its circuit from sudden surges such as the starting load of the wheel-motor, and closes only after a pre-arranged time interval.

A further safety device is provided by a relay 3'4. This relay is connected to the current lead L1 through a limit switch 35 and lead 36. The limit switch 35 is controlled by the movement of the wheel base 18. The switch is closed only when the wheel base reaches its most advanced position. Thereupon the coil of the relay 34 is energized and the switch 41 closed. This arrangement prevents the operation of relay 26 in response to the starting load on the motor circuit.

The secondary side'of transformer 24 is connected to contact 33. The other lead from contact 33 passes through a meter relay 37 by means of lead 38. The output of the meter relay 37 is delivered through an adjustableswitch 39. This switch is connected through lead 40 to the load relay 26. Bysuitable adjustment of the switch 39, the current received in the relay 37 from the transformer 24' will act upon the load relay 26 and open its contact.

The meter relay 37 is also connected to a feed transformer 43. The latter'r'eceives current through contact 41 by lead 42' and from switch 14 through a separate lead. The secondary of transformer 43 is connected to the opposite contact 41 of the relay 34.

As the output current from transformer 24 rises due to the starting load on the motor, the time delay relay 32 is energized. After an appropriate interval during which the starting load has subsided, the contact 33 closes. This supplies current from transformer 24 to the meter relay 37. The lattertreceiving current through closed switch 33 and line 38, operates mechanically to close switch 39 and energize load relay 26. This occurs when the load on the wheel motor rises to a predetermined point.

As the load relay 26 is energized, it opens the circuit to the relay 28. As a result, solenoid 31 is de-energized and the spring 74 shifts the feed selector valve 27 to the left.

Fluid pressure for operating the feed advance through the several valves is supplied from pump 45 through the high pressure pipe 46.

A rapid in-feed valve 47 is connected by line 48 to'the high pressure 46.

The rapid in-feed reversing valve 47 is controlled by a hand lever 75. This operates upon a valve stem 76 which is held in'its outward position by means of the return spring 77;

The reversing valve 47has' two ports 79-80 for directing fluid alternately to opposite sides of pistons 52 and 65. To initiate theoperation of grinding, lever 75 is used to move the valve stem 76 to the right against the force of the spring v7 7 Fluid pressure from line 48 is then discharged through a throttle valve 49 and parallel check valve 50 to line 51. This leads'totlie head of the rapid feed piston 52 in piston cylinder 53.

Piston 52 is moved to the left until the end of the feed screw is engageable' with stop 54. When this stop has been reached, further change in position is made'by shaft 55 operated by hand wheel 56 and its'threaded shaft 57. This is justprior to the anticipated point of pump.

A blocking valve 59 has a free piston 60 which is held in its left position by spring 61. The free piston 60 is in the form of a valve having a single central outlet port.

Low pressure exhaust from the left end of the cylinder 53 is delivered by pipe 62 to the extreme left end of the valve 59. This serves to hold the blocking valve bobbin 60 to the right against the force of spring 61. This blocks the flow of pressure fluid from 48 to the slow feed line 63 and the head end of the slow feed cylinder 64.

As the piston 52 closes line 58, the movement of the piston is cushioned. This leaves only the discharge of exhaust fluid from the cylinder 64 through 62 and throttle valve 68, because it cannot pass through check When the feed screw engages stop 54, the.

4 Fluid pressure from valve 47 through line 70 and through valve 71 is delivered to the middle part of the blocking valve 59 and line 63 to the head end of slow feed cylinder 64.

The slow feed cylinder 64 has a piston 65. The piston rod has parallel rack teeth which engage an elongated pinion 66 on the rapid feed piston52.

Low pressure exhaust from the cylinder 64 passes by lead 67 to port 79 from which it discharges to the sump.

The rate of slow feed is controlled by the throttle valve 71 and is faster than the conventional slow feed.

Normally this will provide a selection of a fast feed followed by a slow feed. However it is the intentionto provide an intermediate feed which will have a feed between that of the slow and rapid positioning feeds. This is accomplished by the feed selector valve 27. The stem 72 of the valve 27 projects to the left through the solenoid 31 for which it forms an armature. The plunger is formed with a valve 73; The plunger is held in the extended position by the spring 74. 7

With the valve 73 in the right-hand position, pressure fluid from 46 enters the valve 27, through check valve 81 and throttle valve 82. It thus supplements the volume' of pressure fluid received from line 70 and valve 71 and directed by blocking valve 59 to the line 63 and the head end of the slow feed cylinder 64. As a result, the slow feed cylinder is therefore moved more rapidly than slow feed, but less than rapid feed.

In short, the operation of the meter relay acting through selector valve 27 is to increase the rate of feed of the grinding wheel beyond the normal slow feed.

The wheel engages the work at the intermediate feed rate and the load on the wheel motor 17 begins to rise. When the grinding load rises to the'point for which the meter relay 37 is set, the current required by motor 17 increases. This current passes through the primary coil of transformer 24 and induces a corresponding increase in current in the secondary coil. This increase in current causes the meter relay 37 to close contact 39, energizing relay 26, opening its normally closed contact, deenergizing relay 28 and opening contacts 29 and 30 to de-energize-31. Valve 73' moves to the left. Fluid from line 46 through valves 81' and 82 is cut ofi, leaving only the fluid from slow feed valve 71'to' contin'ue'the movement of piston 65 at aconventional grinding rate.

If a workpiece is substantially out of round or runs out, the meter relay may be adjusted to function only after the load reaches a point which indicates that the run out has been reduced and the wheel is grinding most of the peripheral surface of the work. Valve solenoid 3 1 and the feed selector valve 73 move'to the left, blockin'gthe supply of fluid under pressure to the fast'feed throttle valve 82 and leaving the slow feed throttle valve as the sole remaining source of fluid under pressure to the head end of slow feed piston 65.

The rate of movement of piston 65 upwardly, and hence, the rate of rotation of feed screw'52'in engagement with '57, determines the rate of advance ofthe grinding wheel to a point suitable for rough grinding.

Thereafter, for each grinding cycle, the grinding wheel will advance rapidly until it almost touches the rough workpiece. It will then continue to advance ata reduced rate. When it engages the work, the feed rate will be reduced still further.

The approach of the grinding wheel 15 to the work 11' is illustrated in'Figure' 1. There is first a'fas't approach until the periphery of the wheel engages the work. This is controlled by the preliminary adjustment of the wheel base 18 and the movement of'the feed piston 52.

Figure 3 illustrates comparatively the saving of time in completing the grinding operation.

The fast approach'time is of course the usual one. However, as the grinding is begun, the diversion of fluid pressure from the fast'feed to the slow feedserves to speed the latter up producing intermediate feed.

The increase of load on the wheel motor is utilized to then interrupt fluid pressure firom the fast feed circuit and leave the slow feed only. By this time however, the rough grinding has progrmsed so that the slow or finish grinding requires materially less time (see Figure 3) with a substantial saving of time for the whole grinding operation.

One advantage of this arrangement is that there is a. pressure operated blocking valve which is connected in a novel manner to delay the forward movement of the slow feed piston until the rapid feed piston has completed its stroke, at which time said blocking valve directs a maximum flow of fluid under pressure to advance said slow feed piston. The pressure for shifting the blocking valve is either exhaust or operating pressure in the rod end of the fast feed cylinder.

Thereafter, when the load on the wheel motor reaches a predetermined point, the selector valve 27 shuts off the supply of fluid to the fast feed throttle valve 53, leaving only the slow feed throttle valve to supply fluid to move slow feed piston 65 at a reduced rate.

An important feature is believed to lie in the rapid advance of the wheel to the point of work engagement and the first change in feed rate which is effected when the blocking valve moves to the left in response to the drop in pressure in line 58, and directs fluid through line 63 to the slow feed piston.

Further advantage lies in maintaining the intermediate feed rate beyond the initial engagement of the wheel with the work until the load increases to a point which indicates that most or all of the out of round conditions have been removed. This is accomplished by an adjustment in the meter relay circuit.

It will thus be seen that the invention provides means to reduce the grinding feed to an intermediate rate of feed on the occurrence of an increase in the motor load and by means independent of the motor circuit.

While the preferred form of the invention has been illustrated by way of example, the invention is believed capable of embodiment with variations in minor details within the scope of the invention as defined in the following claims.

What I claim is:

l. A grinding machine having a grinding wheel support and a work support, a grinding wheel rotatably mounted on said grinding wheel support, a motor for driving said grinding wheel, a source of power for said motor, a lubricant pump for said wheel support, means responsive to lubricant pressure to apply uninterrupted power to said wheel motor, means to feed said wheel support toward said work support at a rapid positioning rate including a hydraulic motor, a second hydraulic motor for feeding saidwheel at a slower rate, means to control said second motor to provide both a fast feed rate and a slower grinding feed rate, a valve for supplying hydraulic pressure to said second motor at one or the other of said rates, a solenoid for actuating said valve, means responsive to said lubricant pressure to actuate said solenoid to supply hydraulic pressure to said second motor at said fast feed rate for elfecting contact of the wheel with the work, and means responsive to an increase in load on said wheel drive motor to actuate said solenoid to change said hydraulic pressure supply from said fast feed rate to said grinding feed rate.

2. In a grinding machine, a grinding wheel support, a grinding wheel rotatably'mounted on said grinding wheel support, means to effect a rapid advance of said grinding wheel, means to interrupt said rapid advance with the grinding wheel a predetermined distance from the axis of the workpiece equal approximately to the maximum radius of an unground workpiece, means to continue the advance of said grinding wheel at an intermediate rate for etfecting engagement of the. grinding wheel with the workpiece, and means for further reducing the rate of feed. after said wheel has ground said workpiece a predetermined amount.

3. In a grinding machine, a grinding wheel support, a grinding wheel rotatably mounted on said grinding wheel support, means to efiect a rapid advance of said grinding wheel, means to interrupt said rapid advance with the grinding wheel a predetermined distance from the axis of the workpiece equal approximately to the maximum radius of an unground workpiece, means operable when the rapid advance of the grinding wheel stops, to continue the advance of the wheel at a reduced rate for an intermediate feed while the wheel engages the work and means for effecting a further reduction in feed rate after grind ing said workpiece a predetermined amount at said intermediate feed rate.

4. In a grinding machine, a grinding wheel support, a grinding wheel rotatably mounted on said grinding wheel support, means to efiect a rapid advance of said grinding wheel, means to interrupt said rapid advance with the grinding wheel a predetermined distance from the axis of the workpiece equal approximately to the maximum radius of an unground workpiece, a feed motor advancing said grinding wheel at an intermediate rate for effecting engagement of the grinding wheel with the workpiece, a supply of fluid under pressure for actuating said feed motor, a pressure operated valve for controlling said supply, and means for actuating said pressure operated valve to prevent the operation of said feed motor during the rapid advance of said grinding wheel.

5. In a grinding machine, a grinding wheel support, a grinding Wheel rotatably mounted on said grinding wheel support, a hydraulic motor for efiecting a rapid advance of said grinding wheel, means to connect the opposite ends of said motor alternately to pressure and exhaust conduits, means to interrupt said rapid advance of the grinding wheel with said grinding wheel a predetermined distance from the axis of the workpiece, a feed screw for advancing said grinding wheel at an intermediate rate for efiecting engagement of said grinding wheel with the workpiece, a second hydraulic motor for rotating said feed screw, a supply of fluid under pressure for actuating said second hydraulic motor, a pressure-operated valve for connecting said second motor with a supply of fluid under pressure, a solenoid operated valve for controlling said supply of fluid to said pressure operated valve, and means for directing exhaust fluid from said rapid feed motor to actuate said pressure-operated valve to prevent the flow of fluid to said second motor while said rapid feed motor is effecting the rapid advance of said grinding wheel.

6. In a grinding machine, a grinding wheel support, a grinding wheel rotatably mounted on said grinding wheel support, a motor for driving said grinding wheel, a hydraulic motor for eifecting a rapid advance of said grinding Wheel, means to interrupt said rapid advance of said grinding wheel with said grinding wheel a predetermined distance from the axis of the workpiece, a feed screw for advancing said grinding wheel at an intermediate rate for effecting engagement of said grinding wheel with the workpiece, a second hydraulic motor for rotating said feed screw, a supply of fluid under pressure for actuating said second hydraulic motor, a pressure-operated valve for connecting said second motor with a supply of fluid under pressure, a solenoid-operated valve for controlling a part of the fluid to said pressureoperated valve, and means responsive to an increase in load on the wheel drive motor for actuating said solenoid-operated valve to cut otf a part of the fluid under pressure to said second hydraulic motor.

7. In a grinding machine, a grinding wheel support, a grinding wheel rotatably mounted on said grinding wheel support, a hydraulic motor for effecting a rapid advance of said grinding wheel, means to connect the opposite ends of said motor alternately to pressure and exhaust 7 conduits; means to interrupt said rapid advance of the grading Wheel, a feed screw for advanci ng said grinding wheel at an intermediate rate for effecting engagefnent of said grinding wheel with the workpiece, a second hydraulic motor for rotating said feed screw, a supply of fliiid under pressure for actuating said second hydraulic r'notor, a pressure-operated valve for connecting said second hydraulic motor with a supply of fluid under pressure, and means for directing exhaust finid from said rapid feed motor to actuatesaid pressure-operated valve to prevent the flowof fluid to said second hydraulic motor while said rapid feed motor is eflfecting the rapid advance of said grinding Wheel.

References Cited in the me of this patent UNITED STATES PATENTS 2,802,312, Gosney Aug. 12, 1957

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