US2340096A - Grinding machine - Google Patents

Description

Jan. 259 1944. S. gE, lWQQDBURY ET A1. 213409096 GRINDING MACHINE Filed Jan. 26, l942 3 Sheets-Sheet l I5 Sheets-Sheet 2 /lllllllIII/IIlI/I/III M W i GRINDING MACHINE Filed Jan. 26, 1942 S. E. WOODBURY ET AL jan. 25, i944.

jxn- 25, 1944- s. E. wooDBuRY ETAL 2,34095 GRINDING MACHINE Filed Jan. 26, 1942 3 Sheets-Sheet 5 im I Zin/enfans I Patented Jan. 25, 1944 GRINDING MACHINE Stephen E. Woodbury and Stephen E. Woodbury, Jr.. Beverly. Mass., assignors to Reid Brothers Company, Inc., Beverly Massachusetts Mass., a corporation of Application January 26, 1942, Serial No. 428,174

4 Claims.

This invention relates to a grinding machine and more particularly to a surface grinding mations 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. 1 is a plan view, with portions broken away, of a grinding machine embodying the present invention; Figs. 2 and 3 are detail views of driving connections to the cross feed mechanism, to be referred to;

mechanism for controlling the driving mechap nism, as hereinafter described.

In accordance with one feature of the present invention, provision is made for operating the reciprocable work supporting table through connections from a reversing motor arranged to be controlled by the movement of the table. Provision is also made in the motor circuit for decreasingthe starting torque of the reversing motor whereby to reduce the shock incident to the change in direction and to contribute in producing smoother table operation and also to reduce to a minimum excessive heating incident to rapid reversal of rotation of the motor. As a further provision for assuring smooth and substantially vibrationless table operation, the connections to the table may include steel bands or straps arranged to be alternately wound and unwound upon a drum, as will be described.

wheel I2 and a longitudinally reciprocablc work supporting table I4. The work supporting table is mounted to slide longitudinally upon ways I6, 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 independently driven by a spindle motor |5, as shown in Fig. 7.

The work supporting table I4 is arranged to be reciprocated through connections including a driving pulley or drum 30 and two steel bands or straps 32, 34, each of which is connected at one end to the driving drum, as illustrated in detail in Fig. 5. The other ends of the straps extend over idler pulleys 36, 38 respectively, and are connected to lugs 40, 42 depending from the opposite ends of the table, as shown in Fig. 4. The idler pulleys 36, 38 are rotatably mounted upon studs 44, 48 supported in the cross slide 20.

Provision is made for driving and reversing the rotation of the drum 30 to cause the straps 32, 34 to alternately Wind and unwind on the drum to effect reciprocation of the table I 4 through connections from a reversing motor 50 as shown in Figs. 1 and 4. The drum 30`is mounted upon and arranged to rotate with a driving shaft 52 journaled in suitable bearings .54, 56 mounted in the machine frame. The shaft 52 is provided with a gear 58 fast thereon which is arranged to mesh with a pinion 60 formed integrally with a clutch member 62 rotatably mounted and longitudinally movable upon a shaft 64. The clutch member 62 is arranged to be moved into operative engagement with a clutch member 65 fast on the end of a shaft' 61 suitably journaled in a gear casing 'ID formed integrally with the motor supporting bracket 12. The shaft 6l is provided with a worm wheel 14 fast, thereon arranged to cooperate with a worm gear I6 secured to the motor shaft 18.

In the illustrated embodiment of the invention, provision is made for disengagirm the movable clutch member 62 from the power driven member 65 when it is desired to move the work supportingtable manually, and as Referring now to the drawings, and particularly to Fig. 4, the grinding machine indicated generally at I0 is provided with a grinding herein shown, the clutch member 62 is arranged to engage a cooperating member fast on the shaft 64, which latter is provided with a hand wheel 82 at its outer end. The shaft 64 is jour- ,naled in a. bearing 83 formed in a bracket 84 detachably secured to the casing 26. The movable clutch member 62 is moved longitudinally to engage and disengage the clutch c'onneciions t5, B by a shifter member 86 adapted to be actuated through connections to a hand lever 88, as illustrated in Fig. 1. The pinion 60 is made wide enough to cooperate with the gear 58 in either of its longitudinally movable positions. As herein shown, the clutch shifter unit, indicated generally at 90, is carried by the detachably mounted motor bracket 'I2 to form an assembled unit therewith.

From the description thus far, it will be observed that the detachable bracket 12 carries the motor driving mechanism and the clutch shifting mechanism as a completely assembled unit which may be conveniently assembled prior to attachment to the casing 26 of the frame. This construction saves time in the assembly operation, renders the parts more accessible for replacement and repair, and results in economy and expediency in manufacture, In assembling the unit, it will be observed that the4 shifter member 86, which may be' forked, is arranged to be received in a grooved portion 92 of the member 62. The unit is attached to the casing 26 by screws 84.

Referring now to Figs. 1, 2 and 3, provision is made in the preferred embodiment of the invention for progressively advancing or retracting the longitudinally reciprocable work table in a transverse direction during the operation of the machine. As herein shown, the cross slide 20 is provided. with a bracket 9S attached to and depending from the underside thereof. A square threaded screw 98, secured at one end to the bracket 96, is arranged to be received in an internally threaded bushing or hollow shaft which in turn is rotatably mounted in a hub |02 formed in the casing 26.

Provision is made for intermittently rotating the hollow internally threaded shaft |00 in either direction to effect transverse movement of the table during the operation of the machine. ris herein shown, the hollow shaft is arranged to be rotated through connections including a crank member |04, a rack |06 connected to and arranged to be reciprocated by the crank, and a gear |03 loosely mounted on the hollow shaft and cooperating with the rack |06. The loosely mounted gear is formed integrally with a pawl carrier ||0 upon which is mounted a double pointed pawl ||2 arranged to cooperate with a square toothed ratchet 4 keyed to the hollow shaft, as illustrated in Fig. 2. Provision is made for adjusting the double pointed pawl ||2 to engage either one or the other of the points with the square toothed ratchet, or to position the pawl in a neutral position. Such adjustment may be effected through a spring pressed ball arranged to be received in depressions in the carrier, as indicated at ||6 in Fig. 2, and may be moved from one position to another by rotating the knob ||8. A hand wheel ||8 also secured to the hollow shaft 00 is provided to permit manual operation of the transverse mechanism when the pawl ||2 is in neutral position.

In operation, when it is desired to eiIect intermittent rotation of the hollow shaft |00 in a counterclockwise direction, the pawl |I2 may be positioned as indicated in Fig. 2 'so that when the pawl carrier ||0 is rotated in this direction by the reciprocating rack |06 and the gear |00. the pawl ||2 in engagement with the ratchet will rotate the hollow shaft in a counterclockwise direction. On the return stroke of the rackiil, the pawl will slide over the ratchet teetl-. It will be clear that when the pawl is positioned to engage the second point thereof with the square toothed ratchet, rotation of the hollow shaft |00 in the reverse direction will be effected. Thus it will be seen that the internally threaded hollow shaft |00 in cooperation with the square threaded screw is operative to effect transverse movement of the cross slide 20 and the table I4 supported thereon, in either direction during the operationof the machine. As illustrated in Figs. 1 and 2,the'reciprocated rack |06 is received in a guide |20 formed integrally with a sleeve |22 loosely mounted upon the hollow shaft |00 to permit relative movement of the-supporting sleeve |22 during the angular movements of the rack |0E`as reciprocated by the crank |04.

Referring now to Figs. 1 and 3, the mechanisrn for rotating the crank member |04 will be described. As therein shown, the crank member is clamped fast upon the end of a stud |24, rotatably mounted in a bearing" |26 formed in the bracket 84. 'I'he stud |24 extends from and is formed integrally with a, pawl carrier |28 in which two pawls |30, |32 are mounted and arranged to cooperate with a square toothed ratchet |34. The square toothed ratchet |34 is formed integrally with and is arranged to rotate with the driving gear 58. As above described, the driving gear 58 is arranged to change its direction of rotation during the operation of the machine.- Thus, in operation, when the ratchet |34 is rotated in a clockwise direction, the pawl |30, see Fig. 3,. will be operative to rotate the crank through a predetermined stroke until the tail of the pawl engages a pawl stop |36 extending from the bracket 84, see Fig. 7, to disengage the pawl |30 from its ratchet |34. Thereafter, during the remainder of the clockwise movement of the ratchet I 34, the other pawl |32 will slip over the ratchet teeth. When the direction of rotation is changed, the pawl |32 becomes effective to rotate ythe crank as above described, until it in turn is disengaged from the ratchet by the pawl stop |38. Thus it will be seen that each time the crank is rocked in either direction the rack |03 is reciprocated to effect rotation of the hollow shaft |00 in the desired direction as determined by the adjusted position of the double pointed pawl ||2. The rack |06 is secured to the crank |04 in a T-slot |05 to permit convenient adjustment of the length of stroke.

From the description thus far it will be observed that the detachable bracket 84 carries the crank driving mechanism and the connections for manually operating the machine as a completely assembled unit which may be conveniently assembled prior to afllxing the bracket to the casing 28. Thus, the assembly oi' this portion of the machine is facilitated, the parts rendered more accessible for adjustment or replacement and the structure results in economy in manufacture.

Provision is made for permitting lateral movement 'of the driving drum 30 on its shaftl 52 during the transverse movement of the cross slide 20. As herein shown, the shaft 52 is provided with three raceways |40 in which ball bearings |42 disposed in the drum 30 are arranged to run. As shown in Fig. 6, the ball bearings are retained in the drum by spring wire rings arranged to be received in grooves |44 provided in the drum. The rings may be open to enable them to be contracted and forced into the grooves where they may again expand into a position to prevent escape of the lball bearing members from the drum. Thus, it will be seen that the bearing members |42 serve as a driving connection between the shaft 52 and the drum 30 and also permit lateral movement of the drum ln a smoothly operating manner, thus reducing friction and tendency to bind on the shaft to a minimum. As shown in Figs. 1 and 4, the bracket Q6, attached to the cross slide 20, is provided with arms M5, Nt arranged to embrace the drum 30. and to move it along the shaft 52 in alignment with the longitudinally reciprocabletable Il as the cross slide is moved transversely.

Referring now to Figs. 1 to 8, provision is made for controlling the reversible motor 50 to effect a change in direction of rotation thereof through connections from the reciprocable work table |41. As herein shown, a reversing switch |50 mounted in the cross slide 2|) is arranged to be operated by dogs |52, |54, adjustably supported upon and movable with the table I4. The reversing switch comprises a slidingly mounted stud |56 arranged to be reciprocated by a pivotally mounted arm itt which is received in a slot in the stud |56. An operating arm I, fast on the pivot shaft H52 is provided with pins |54, |65, arranged to be engaged by the dogs |52, |54, respectively, at the end of the predetermined longitudinal movement of the table. The switch stud |55 is providedwith contacts |53, |11) and in operation, when a dog engages the switch l50, it operates to first open the prevailing circuit to the motor 0 and then close a second circuit to operate the motor in a reverse direction. .A handle itl is also provided on the -operating arm |55 to permit the switch to be manually operated when desired. A safety switch, indicated at |12, may also be provided to be operative to open the entire circuit in the event the dogs |52, H54 areremoved or become loosened. As illustrated in Fig. Il, cam pieces |14, |16 supported on the underside of the table lll are arrangedA to engage and depress the switch member |12 to open the circuit at contacts |18 when the table overrides or fails to engage the reversing switch |50. The reversing switch may and preferably will be of standard construction. A

As illustrated in Fig. 8, the wiring diagram therein shown includes connections to the grinding head motor l5, and to the reversing motor 50. Stop and start switches |82, |84 are arranged to open and close a circuit to a primary magnetic switch |85 which closes the circuits to the grinding head motor and to the reversing motor at contacts |86, |81, |88 and |89. The reversing switch, indicated at |50 operates to alternately open one circuit and close another to the magnetic switches |90, |92 for alternately opening and closing the circuits to the reversing motor 50 at contacts |94, |95, |96, |91, whereby to reverse the direction of the current through the motor so that its direction of rotation is reversed. The safety switch is indicated at |12 and a manually operated switch |98 may also be provided for opening the circuit to the reversing switch |50. It will be observed that the wire 2||l is preferably led through contacts 2|2, 2|4 of the reversing switch in order to open the circuit through all three wires 2|0, 2li, 2|8 simultaneously when the on and off switch 22C is turned off.

Thev table driving motor 50 is preferably of the squirrel-cage polyphase induction motor type and is started by placing the same directly across the line and is stopped and reversed by reversing the connections to two wires of the primary winding 200 of the motor at the time the motor is still operating at full speed in the original direction. 'I'his motor is required to develop considerable power since in addition to overcoming the friction load of the table it must also overcome the inertia'load thereof during rapid starting and stopping as well as the inertia load of the motor rotor, which may be comparable in amount to the inertia load of the table. During the stopping operation the voltage developed by continued rotation of the motor in its original direction due to inertia after the connections to the motor have been reversed effectively adds to the applied voltage to increase the current instead of opposing the applied voltage as in motors under normal operation.

' Standard motors have been found to take excessive current with resulting overheating under these conditions and to produce torque which is too-high resulting in too rapid stopping and reversal with constant deleterious shocks and jars to the machine parts. Complicated control circuits such as those involving insertion of resistance into the motor circuit under starting and reversing conditions are not satisfactory because of added expense and also because of failure of the control system under rapid repetition of op eration. Increasing the size of a standard motor does not solvevthe problem, as this increases the inertia load because of the larger size rotor required.

.It has been found that the structure of the motor itself can be modified to reduce the starting and reversingcurrent and torque. This may be accomplished bykincreasing the number of turns in each phase of the primary winding of the motor 5U for a given applied voltage-so as to decrease the current as well as the torque during starting and reversing. In standard motors the number of turns in the primary winding is such that the flux necessary to develop a back volta-ge substantially equal to the applied voltage is just slightly less than that which will saturate the iron of the motor in the portions of the iron having maximum flux density. That is to say, in a standard motor the maximum flux is just slightly less than that which will pass the knee of the magnetization'curve of the iron. By substantially doubling the number of -turns normally employed for a given voltage and iron structure, for example using approximately 1% to 21A times the number of turns usually employed, the flux necessary to produce a back voltage substantially equal to the applied voltage is reduced, the flux being substantially inversely proportional to the number of turns in the primary Winding. By employing a primary winding which results in a iiux which is not substantially greater than one-half of that necessary to produce saturation it has been found that the motor starts and reverses smoothly without tak-1 ing excessive current.

With the motor employed in the present invention in which the number of turns in the primary winding is increased, the lesser amount of flux causes the torque during starting and reversing to be materially reduced and as the speed is low under these conditions the internal power total starting and reversing current is therefore materially reduced. This current may be considerably greater than full load current under steady load conditions but is much less than that taken by standard motors having primary windof said iron so as to provide a torque eliminating ings designed to operate with the iron adjacent the air gap nearly at saturation during periods of maximum iiux. Thus the motors employed in the present invention do not overheat and also develop a relatively low reversing and starting torque, producing smooth operation of the machine without jar or shock. It will be seen that the. motor forming a part oi! the present invention is particularly adapted for the operation of machines having reciprocating tables with the motor'electrically connected directly to a power line and mechanically connected to the table without intermediate reversing mechanisms so as to start, stop and reverse the table by merc reversal of the electrical connections.

'While the invention is particularly useful in connection with a grinding machine embodying a reciprocable work supporting table and drivin-g mechanism including a reversing induction motor of the character described, nevertheless viewed in its broader aspects the invention may include other types of machines wherein a reversible element, either of the reciprocating, rotating, or oscillating type, is arranged to be driven by a reversing induction motor having the characteristics and in the manner above described.

While the preferred embodiment of the invention has been herein illustrated and described, it will be understood that the invention may be embodied in other forms within the scope of the following claims.

Having thus described the invention, what is claimed is:

1. In a grinding machine, in combination, a longitudinally reciprocable work supporting table, driving mechanism for reciprocating said table including a. reversing motor of the induction type having a primary winding, an electrical circuit for said motor for connecting said primary winding directly to a power line to apply full line voltage to lsaid motor during starting and reversing of said motor, a switch in said circuit for effecting reversal of said motor, means carried by said work table for operating ,said switch when the table is moved a predetermined distance in either direction, the primary Winding of said motor being wound to produce a maximum flux in the' iron of said motor not substantially greater than half that causing saturation abrupt reversal and insuring smooth starting movement.

2. In a grinding machine, in combination, a reciprocable work supporting table, driving mechanism for reciprocating said table including a reversing motor oi the inductiontype having a primary winding, means for automatically controlling the reversing oi' said motor` to reciprocate said table, said means applying full line voltage to said primary winding during reversing of said motor, said primary windingbeing provided with substantially twice the number of turns which will produce a maximum iiux in the iron causing saturation thereof, whereby the current taken by said motor is maintained below that which will cause overheating and the torque produced by said motor during starting and reversing is suiilciently low to eliminate abrupt reversal and insure smooth starting movement.

3. In a grinding machine, in combination, a reciprocable work supporting table, driving mechanism for reciprocating said table including a reversing motor of the induction type having a primary winding, means for automatically controlling the reversing of said motor to reciprocate said table, said means applying full line voltage to said primary winding during reversing of said motor, Ithe primary winding of said motor being wound to produce a maximum iiux in the iron of said motor not substantially greater than half that causing saturation of said iron so as to provide a torque eliminating abrupt reversal and insuring smooth starting movement.

4. In a machine tool, in combinatiom'a work holding member and a tool member, one of said members being movable relative to the other member, driving mechanism for movin-g said one member alternately in opposite directions including a reversing motor of the induction type having a primary Winding, means for automatically controlling the reversing of said motor to alternately drive said one member in opposite directions, said means applying full line voltage to said primary Winding during reversing of `said motor, the primary winding of said motor being wound to produce a maximum'ux in the iron of said motor not substantially greater than half that causing saturation of said iron so as to provide a torque eliminating abrupt reversal and insuring smooth starting movement.

STEPHEN E. WOODBURY. STEPHEN E. WOODBURY, JR.

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