US2370701A - Grinding machine - Google Patents

Description

March 6, 1945. s. E. WOODBURY GRINDING MACHINE Filed April 13, 1943 2 Sheets-Sheet l y INVENTOR.

guy ML, m w i March 1945. s. EIWOODBURY 2,370,701

GRINDING MACHINE Filed April 15, 1943 2 Sheets-Sheet 2 162 164 v J50 196 A Jr-vzr are l- 0: El 170 M 2 2' 5186i 194 i196 155% 169 his 192 INVENTOR.

I J-l l What Patented Mar. 6, 1945 GRINDING moms Stephen E. Woodbury, Beverly, Mass., asslgnor to Reid Brothers Company, Inc., Beverly, Mass, a corporation of Massachusetts Application April 13, 1943, Serial No. 482,838

9 Claims.

This invention relates to a grinding machine and more particularly to an electrical control mechanism for an automatic surface grinding machine.

The invention has for an object to provide a machine tool such as a grinding machine, and particularly an automatic surface grinding machine with a novel and improved electrical control mechanism for controlling the operation of the machine and which is particularly useful in an automatic surface grinding machine to enable the latter to be operated in a safe, efficient and superior manner.

With this general object in view and such others as may hereinafter appear, the invention consists in the machine tool, and particularly the surface grinding machine, and in the various structures, arrangements and combinations of parts hereinafter described and particularly defined in the claims at the end of this specification.

In the drawings illustrating the preferred embodiment of the invention, Fig. l is a front elevation, partly in cross-section of a suflicient portion of a surface grinding machine embodying the present electrical control mechanism to enable the invention to be understood; Fig. 2 is a wiring diagram illustrating the present control mechanism as embodied in a grinding machine,

to be hereinafter more fully described; Fig. 3 is a detail view of a solenoid operated brake embodied in the present grinding machine, and Fig. 4 is a modified form of braking mechanism to be referred to.

In general, a surface grinding machine embodying the invention is provided with a longitudinal work supporting table for holding and moving the parts to be machined with cross feed mechanism for progressively moving the work supporting table in a transverse direction relative to the grinding wheel. Provision is made for operating the reciprocable work supporting sition such as to overbalance the table on its support, causing damage to-the table Or the machine and possibly to the operator. Accordingly, one feature of the present invention contemplates the provision of a safety or limiting switch designed to be engaged to open the electrical circuit to the driving motor when the table approaches a dangerous position. In the preferred embodiment of the invention, a spring-pressed, normally closed contact member is employed in the safety switch, so thatupon engagement thereof by limiting stops on the table, the power is immediately cut off not only from the table motor but also from the grinding wheel motor.

In the operation of a surface grinding machine, a possibility exists that the momentum of the table might be sumcient at times to carry the table limiting stops beyond the safety switch whereupon the spring operated contact member would immediately reestablish the circuit and permit continuance of the table movement. In

table through connections from a reversible motor arranged to be controlled by the movement of the table.

In the operation of the surface grinder the table is limited in its movement in either direcorder to overcome this defect the safety switch is preferably placed in the circuit in series with the solenoid of the primary magnetic switch, as will be hereinafter more fully described, whereby opening of the circuit'at the safety switch will effect opening of the primary magnetic switch, so that the safety switch will not be effective to reestablish the connection to the driving motor in the event that the table overrides the safety switch, as above described, or overbalances so as to lift the limiting stops out of engagement with the safety switch.

Another feature of the present invention relates to the provision of a solenoid operated brake in the control circuit for braking, the table driving motor so as to bring the latter to rest promptly upon interruption of the circuit and thus prevent the table from coasting to a dangerous position. As above described, under normal operating conditions, the table is limited in its movement in either direction by a reversing switch actuated by operating dogs carried by the table which maybe adjusted to reverse the movement of the latter at predetermined limits. In practice such mechanism normally operates to reverse the table promptly at either end of its stroke. However, in prior control mechanisms in the event that the power to the table driving motor was cut off at an intermediate point in the stroke such as by turning the "on-off switch to off or by pressing the stop button,,the table was free to continue in motion until stopped by incidental friction. In accordance with the present invention, the solenoid of the solenoid operated brake is preferably arranged in parallel with the primary magnetic switch solenoid so that upon pressing the stop button, the table will be brought to rest immediately at any desired position within the limits of its normal stroke. Furthermore, in the event that the table should be inadvertently moved beyond its normal limits, as above described, to out off the power at the safety switch, the brake would likewise be applied to prevent the table from gerous position.

Referring now to the drawings, the present invention is preferably illustrated as embodied in a grinding machine indicated generally at I which is provided with a grinding wheel I2 and a longitudinally reciprocable work supporting table I4. The work supporting table is mounted to-slide longitudinally upon way I8 provided in-a cross slide 20 which, in turn, is adapted to be moved transversely in ways 22, 24 formed in the top of a casing 26 mounted upon the base 28 of the machine. The grinding wheel I2 is mounted upon a spindle I3 and is driven by a spindle motor I as diagrammatically shown in Fig. 2.

In the illustrated surface grinding machine, the work supporting table is arranged to be reciprocated through connections including a driving sprocket gear 30 and a sprocket chain 82, 34 which extends around the lower part of the sprocket gear 30 and over idler sprockets 86, 38 respectively and connected to lugs 40, 42 depending from the opposite ends of the table.

Provision is .made for driving and reversing coasting to a danthe rotation of the sprocket gear 80 to cause the chain 32, 84 to alternately effect reciprocation of the table I4 through connections from a reversing motor 50. The gear 30 is mounted upon and arranged to rotate with a driving shaft 52 which is provided with a gear 58 fast thereon arranged to mesh with a pinion 80 comprising part of a clutch member (not shown) adapted to be operatively connected to a shaft 61. The shaft 61 is provided with a worm wheel 14 fast thereon arranged to cooperate with a worm 16 secured to the reversing motor shaft 18.

Provision is made for controlling the reversible motor 50 to efiect a change in direction thereof through connections from the reciprocable work table I4. As herein shown a reversing switch 7 I50 mounted in the cross slide is arranged to be operated by dogs I52, I54 adJustably supported upon and movable with the table I4. The reversing switch comprises a slidingly mounted stud I58 arranged to be reciprocated by a pivotally mounted arm I58 which is received in a slot in the stud I58. An operating arm I80, fast on the pivot shaft I62 is provided with pins I64, I65, arranged to be engaged by the dogs I52, I54 respectively at the end of the predetermined longitudinal movement of the table. The switch stud I56 is provided with contacts I68, I10 and in operation, when a dog engages the switch I50, it operates to first open the prevailing circuit to the motor 50 and then close a second ,circuit to operate the motor in the reverse direction. A handle I6I is also provided on the operating arm I80 to permit the switch to be manually operated when desired.

As illustrated in Figs. 1 and 2, a safety switch I12 is located beneath the table I4 substantially centrally in the machine. It is operative to open I14, I16 supported on the underside of thetable I4 either of which is arranged to engage and depress the switch member I12 to-open the circuit at contacts I18 in the event that the table should override or inadvertently fail to engage the reversing switch I50.

Referring now particularly to Fig. 2, the illus- I trated controlling apparatus comprises a primary circuit including connections to the grinding head or spindle motor I6, and the reversing motor 50. Stop and start switches I82, I84 are arranged to open and close a relay circuit to the solenoid I85 of a primary magnetic switch I86I81I88 which closes the circuits to the grinding head motor and to the reversing motor at contacts I88 and I89. The reversing switch indicated at I50 operates to alternately open one circuit and close another to the solenoids I90, I92 for alternately opening and closing the circuits to the reversing motor 50 at contacts I84, I95, I96 and I91 whereby the direction of rotation is reversed.

From the description thus far it will be observed that under normal operating conditions, when the on-off" switch I98 is moved to its on position and the start button I82 is pressed the solenoid I85 of the primary magnetic switch I86I81-I88 is energized to close the circuits to the spindle motor I5 and the table motor 50, and that the direction of rotation of the motor 50 will be reversed to reciprocate the table I4 each time the latter reaches its limit of movement in either direction as determined by the adjustment of the reversing dogs I52, I54. In the event that the reversing dogs become loosened or are improperly adjusted, or, upon failure of the reversing switch I50, the table will continue to be driven in the prevailing direction until either of the limiting stops I14, I16 engages the spring-pressed safety switch I 12. As herein shown, the safety switch contacts I18 are preferably arranged in series with the primary magnetic switch solenoid I85. With this construction, when the circuit is interrupted at the safety switch contacts I18, the primary magnetic switch solenoid will be deenergized to open the circuits to the spindle motor I5 and the table motor. and, such circuits cannot be reestablished until two conditions are satisfied. First, the table must be manually moved back to within its nor-' mal range of movement to reset the safety switch contacts and second, the start button must be pressed. In this manner, the possibility of reestablishing the circuit through the safety switch contacts alone is eliminated, since, in the event the momentum of the table should carrythe limiting stops beyond the safety switch, or, in

the event the table should be overbalanced and lift up so as to permit the safety switch contacts to again be connected, it would still be necessary to press the start button before the circuits to the motors would again be reestablished. In any event, positive driving of the table beyond the limit defined by the safety switch is entirely terminated.

- The solenoid brake, as shown in Figs. 1 and 3, and indicated generally at 200 comprises a shoe type spring set brake which is maintained in its inoperative or oil position when the current is on and which is released to apply the brake when the current is cut off. As herein shown, the motor shaft 18 may be provided with a relatively small pulley 202 and the braking unit may be supported on a shelf 204 adjacent the motor. In operation, when the solenoid 206 is energized, the

brake shoes 288 are held away from the pulley to permit normal operation of the machine. However, when the circuit is interrupted as above described, the solenoid 208 is deener gized thus releasing the spring 2! to permit the brake shoes 288 to be applied to the wheel 202. As diagrammatically illustrated in Fig. 2, the brake solenoid 288 is arranged in parallel with the primary switch solenoid I85 so that upon interruptionof the circuit at either the on-off switch I88, the stop button I84 or the safety switch I12 the brake solenoid will be deenergized to bring the table to rest promptly.

Referring now to Figs. 1 and 4, a modified form of braking mechanism, indicated generally at 88,

comprises an electrically operated brake or friction shoe 82 adapted to frictionally engage the underside of the work table 14 when the current is cut off, and which is electromagnetically maintained in its inoperative position when the current is on. As herein shown, the modified braking unit includes a. solenoid 84 arranged to hold the brake shoe 82 down away from the underside of the table H against the resistance of a pair of coil springs 86. In the circuit shown in Fig. 2, the solenoid 84, see Fig, 4, may replace the solenoid 206 shown in Fig. 2, so that in operation, when the solenoid 84 is energized, the friction shoe 82 is held away from the reciprocable table H to permit normal operation of the machine.

However, when the circuit is interrupted, as above described, the solenoid 88 is deenergized thus releasing the springs 86 to apply the brake.

From the above description it will be seen that the present invention enables the machine to be controlled in a simple and efficient manner to provide a maximum of safety for the operator and a minimum of liability of damage to the machine.

Although the present control mechanism is preferably illustrated herein as embodied in a 2. In a grinding machine, in combination, a reciprocable work supporting table, driving mechanism for reciprocating said table including a reversing motor, a primary electrical circuit for said motor including a solenoid operated primary switch, a stopping and starting switch for controlling the action of said primary switch, a reversing switch for eifecting reversal of the motor, means carried by the table for operating Having thus described the invention, what is claimed is: v

1. In a grinding machina'in combination, a reciprocable work supporting table, driving mechanism for reciprocating said table including a reversing motor, a primary electrical circuit for said motor including a solenoid operated primary switch, a stopping and starting switch for controlling the action of said primary switch, a

reversing switch for effecting reversal of the motor, means carried by the table for operating said reversing switch when the table is moved into a predetermined position in either direction, and a afety switch arranged to be engaged by the table to open the circuit to the primary switch and thus stop the motor in the event that the table should inadvertently override said predetermined position, said safety switch being arranged in series with said primary switch solenoid whereby to interrupt the motor circuit andprevent reestablishment thereof until the table is moved back to within its normal range of movement and the starting switch is operated.

.said reversing switch when the table is moved into a predetermined position in either direction, and a safety switch arranged to be engaged by the table to open the primary switch and thus stop the motor-in the event that the table should inadvertently override said predetermined posi- ,tion.

3. In a grinding machine, in combination, a reciprocable work supporting table, driving mechanism for reciprocating said table including a reversing motor, a. primary electrical circuit for said motor including a primary magnetic switch, a stopping and starting switch controlling the action of said primary switch, a reversing switch for efiecting reversal of the motor, a limiting dog carried at each end of said table for operating said reversing switch when the table is moved into a predetermined position in either direction, and a spring-pressed safety switch arranged to be engaged by the table to open the primary switch and thus stop the motor in the event that the table should inadvertently override said predetermined position, said safety switch being arranged in series with the solenoid of said primary magnetic switch whereby to prevent reestablishment of said motor circuit until the ta ble is moved back to within its normal range of movement and the starting switch is also operated.

4. In a grinding machine, in combination, a reciprocable work supporting table, driving mechanism for reciprocating said table including a reversing motor and a motor shaft, an electrical a single centrally'located safety switch arranged to be engaged by the table to open the primary switch and thus stop the motor in the event that the table should inadvertently override either of said predetermined positions, said safety switch being arranged in series with said primary switch solenoid whereby to prevent reestablishment of said motor circuit until the table is moved back to within its normal range of movement and the starting means is operated, a spring-actuated brake associated with said motor shaft, and a solenoid connected in parallel with the primary switch solenoid arranged to release said brake to bring said motor to an abrupt stop when said stopping means or said safety switch is operated to interrupt the current tosaid primary switch.

5. The combination with a machine tool provided with a movable member arranged to normally travel within predetermined limits, of driving mechanism for said movable member including a motor, a. primary circuit for said motor including a solenoid operated primary switch, and

switch and thus stop the motor in the event that said movable member inadvertently overrides its normal predetermined limits.

6. The combination with a machine tool'pro-= vided with a, movable member arranged to travel within predetermined limits, of driving mechanism for said movable member including a motor and a motor shaft, a circuit for said motor including a solenoid operated primary switch, and a safety switch connected in series with said primary switch solenoid and arranged tobe engaged by said movable member to open said primary switch and thus stop the motor in the event that said movable member inadvertently overrides its normal predetermined limits, a-spring-operated brake associated with said motor shaft, and a solenoid connected in parallel with said primary switch solenoid arranged to release said brake to bring said motor to an abrupt stop when said primary switch-is opened.

7. In a grinding machine, in combination, a reciprocable work supporting table, driving mechanism for reciprocating said table including a reversing motor, an electrical circuit for said motor including a solenoid operated primary switch, a reversing switch for effecting reversal of the motor, means carried by the table for operating said reversing switch when the table is moved-into 4 a predetermined position in either direction, and

a solenoid operated brake connected in parallel with the primary switch solenoid arranged to engage said table and bring it to an abrupt stop when said primary switch is opened.

8. In a. grinding machine, in combination, a reciprocating work table, a reversible motor for driving the table, a grinding head having an individual motor, a primary circuit for operating both motors including an electro-magnetic switch, means operated by the table at each end of its normal travel, for reversing the table motor, and a single safety switch operated by the table in reaching a position beyond its normal path of travel in either direction for opening said electromagnetic switch and stopping both the said motors.

9. In a grinding machine, in combination, a reciprocating table, a reversible motor therefor. 23. motor circuit including primary and reversing switches, dogs carried by the'table for operating the reversing switch .at each end of the normal travel of the table, a single safety switch located substantially centrally beneath the path oi the table for controlling said primary switch, and

separate means carried by the'table for-tripping the safety switch and operating when the table moves in either direction beyond its normal path 01 travel.

STEPHEN E. WQODBURY.

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