US2153516A - Electrically operated lifting jack - Google Patents

Description

April 4, 1939. K. ECK

ELECTRICALLY OPERATED LIFTING JACK Filed Nov. 2, 1937 4 Sheets-Sheet l ATTORNEY April 4, 1939. E 2,153,516

I ELECTRICALLY OPERATED LIFTING JACK Filed NOV. 2, 1937 4 Sheets-Sheet 2 V47 ZINEENTZR 4 Sheets-Sheet 3 K. ECK

ELEOTRICALLY OPERATED LIFTING JACK Filed Nov. 2, 1937 April 4, 1939.

ATTORNEY April 4, 1939. K. ECK

ELECTRICALLY OPERATED LIFTING JACK 4 Sheets-Sheet 4 Filed Nov. 2, 1937 'ATTORNEY POWER LINE INVENTOR 74.! 14,

Patented Apr. 4, 1939 UNITED STATES PATENT OFFICE ELECTRIGALLY OPERATED LIFTIN G JACK Application November 2, 1937, Serial No. 172,358

15 Claims.

' This invention relates to lifting jacks which are operated by electric motors to raise and lower the load.

It is an object of the invention to provide an improved electrically-operated lifting jack, and

one that can be operated by inexperienced persons without the possibility of ever overrunning the set limits of movement.

It is customary to provide a limit switch of some form to cut off the power to the motor when the jack approaches its upper or lower limit of movement. When the jack is wired in such a way that the motor turns in the wrong direction, the limit switches may be ineffective. For exam- 5 ple, if the motor is running with the wiring such that a down movement against the limit switch is required to cut off the power supply, but the direction of rotation of the motor is causing the jack to rise, then the switch means can not operate automatically to stop the jack from moving too far.

Such a situation may arise because of a mistake in originally wiring the jack, but in the case of portable jacks which are plugged in to a power line wherever they happen to be used, the direction of rotation of the motor may be reversed by a change in the polarity of the'power line conneotions. In a three-phase motor the exchanging of any two wires will reverse the motor.

With stationary machinery the electrician that installs the machinery must, by trial, find the proper connections for the various wires. This can hardly be expected in the case of a portable tool. This invention makes such trials unnecessary by providing a phase-changing switch that operates if the motor does not rotate in the right direction to make the limit switches effective.

Other objects, features and advantages of the invention will appear or be pointed out as the 40 specification proceeds.

In the accompanying drawings, forming part hereof:

Fig. 1 is a front elevation, partly broken away and partly in section, on the line ll of Fig. 2, showing a jack embodying this invention;

Fig. 2 is a side view partly in elevation with the gear case cover removed and partly in section approximately on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged sectional view of the switch box, most of the section being taken on the line 3--3 of Fig. 2;

Fig. 4 is a detail view of a part of the structure shown in Fig. 3, illustrating its method of operation;

Fig. 5 is an enlarged sectional view taken on X the line 5-5 of Fig. 1; and

Fig. 6 is a wiring diagram of the jack shown in the other views.

The jack comprises a frame ll having a base 5 l2 and bearings in which slides a lifting head or ram M. The ram has a nut l5 through which threads an actuating screw l6 supported by the base l2. A bevel gear l8 connected to the bottom portion of the screw I6 is rotated by a smaller 10 bevel gear 20 on a horizontal shaft 2| with a large spur gear 22 (Fig. 2). A key 23 fastened in the frame H keeps the ram M from rotating.

Power to drive the gear 22 is supplied by an electric motor 24 through the reduction gearing shown in Fig. 2. There is a small gear 25 on the motor shaft, and both a small and a large gear on each of three shafts 21, 28 and 29, the small gear on each shaft meshing with the large gear on the next shaft so as to reduce the speed and increase the force of the rotary motion transmitted from the motor to the screw I6.

There is a brake drum 3| on the motor shaft, and a brake shoe 33, supported on a pivot 34, is held against the brake drum 3| by a spring 36 with sufiicient force to keep the gearing and motor from turning when the power to the motor is shut off.

A push rod 38 is loosely held in bearings 39. An adjustable shoulder 40 threads over one end of the push rod 38 and can be held in set position by a lock nut 4|. The push rod 38 extends through an upstanding end of the brake shoe 33 which is held against the shoulder 40 by a spring 42 surrounding the end portion of the push rod.

The other end of the push rod 38 forms a blunt point that fits into a V notch 44 in the face of a cam 45. This cam is secured to a shaft 46, and the shaft is oscillated by a link 41 connected at its lower end to a crank 48 of the shaft 46 and at its upper end to a lever 49, best shown in Fig. 1.

The lever 49 is secured to one end of a shaft 5 I. This shaft extends through a switch box 52 and projects through the front face of the switch box.

A handle 54 fastened to the projecting end of the shaft 5| is moved into different positions to control the operation of the jack. In Fig. 1, the handle 54 is shown in its middle, neutral position. The free end of the handle 54 is raised to cause the jack to rise and is pushed down to cause the jack to lower, as indicated by legends Up and Down on the cover of the switch box.

A block 56 fastened to a lever 51 extends into a groove 58 in the side of the ram I 4. The ends of the groove 58 (Fig. 2) form abutments 60 and shaft 46.

6| which strike the block 56 to move it whenever the ram I4 approaches the lower and upper limits of its travel.

Referring again to Fig. 1, the lever 51 has a fulcrum 63 at one end, and is connected at its other end with the lever 49 by a link 65. This connection causes the handle 54 to move when the block 56 on lever 51 is shifted up or down by the abutments 60 and 6| on the ram I4. If the handle 54 is in the down position when the abutment 60 comes against the block 56. the link 65 is pushed down and the handle 54 is raised into the neutral position shown in the drawings. With the handle 54 in its up position, movement of the block 56 by the abutment 6| as the ram approaches the limit of its upward movement raises the link 65 and shifts the handle 54 down into neutral position.

This movement of the link 65 causes the link 41 to move in the same direction and rotate the position, the link 41, shaft 46, and cam 45 will be in the positions shown in Fig. 2 with the notch 44 in line with the push rod 36. When the end of the rod is in the notch 44, the brake shoe 33 is against the drum 3|. and the brake is applied. Any angular movement of the cam 45 in either direction causes the sloping sides of the notch 44 to thrust the push rod 38 toward the left and release the brake. Thus, the brake is applied only when the handle 54 is in neutral position, and the design of the cam 45 is such that it releases the brake before the switches of the motor circuit have moved far enough to close. The brake can be operated only through the cam 45.

The structure enclosed in the switch box 52 is shown in Figs. 2-5. Referring first to Fig. 2, there is a cam 61 rigidly held on the shaft by a set-screw 68. Two switch arms 69, 10 on the shaft 5| are free to turn on the shaft 5| but are yieldably held in a predetermined angular relation with the shaft 5| and cam 61 by spring pins 12 (Fig. 3) which slide in recesses in the switch arms and project into a notch 13 in the cam 61. I

The switch arm 69 carries a block 14 made of insulating material. A spring 15 which urges the pin 12 against the cam 61 is compressed between the pin 12 and block 14 and is strong enough to bring the switch arm 69 back to its normal angular relation with the cam 61 and shaft 5| whenever the switch arm is moved and the pin 12 displaced upward along the sloping sides of the notch 13.

A contact 16 extends through the block 14 and a side contact 11 connects with the contact 16. This side contact 11 rubs against a stationary plate 19 (Fig; 2) secured to an insulating frame 00 fixed to the switch box 52. The off-side location and action of the spring 15 in arm 69 holds side contact 11 against the plate 19. There are other contacts on the frame 00 in position to be touched by the contact 16 when the switch arm 69 moves. These other contacts are best shown in Fig. 3 and include a contact 82 against which the contact 16 comes when the switch arm 69 is moved clockwise and a contact 83 in position to limit counterclockwise movement of the switch arm contact 16.

The construction of the switch arm 10 (Fig. 2) is similar to that of the switch arm 69 except that its spring and its side contact are on the other side. Reference characters 86, 81, 89, 92 and 93 are used to indicate the contacts for switch When the handle 54 is in neutral position. A similar action is obtained arm 10 which correspond with the contacts 16, 11, 19, 82 and 83, respectively. Not all of the contacts for switch arm 10 can be seen in Figs. 2 and 3, but they are indicated in the wiring diagram (Fig. 6).

Referring again to Fig. 3, the cam 61 has recesses 95, 96 and 91 with raised portions 98 and 99 between these recesses, and flanks I00 and IN beyond the outer recesses. A plunger I03, urged toward the cam 61 by a spring I04, has a conically shaped and rounded end which enters any of the recesses 95, 96 or 91 to hold the cam 61 and the shaft 5| in any one of three angular positions, corresponding to the up, down, and neutral positions of the handle 54 (Fig. 1) by which the shaft 5| is turned. The movement of the cam 61 from notch 96 to 95 is greater than that required to close contact 16 against contact 82 in order to insure a good electrical contact, and on opening the switch the contact 16 will remain against the contact 82 because of the spring action of pin 12 until the plunger I03 enters the recess 96 and effects a quick movement of the switch arm into neutral when the switch is closed in the other direction.

There is a cross shaft I06 (Fig. 3) below the plunger I63, and there is a gear segment I01 fixed on the shaft I06 and meshing with teeth on the bottom of the plunger. A crank arm I09 has its upper end formed into a clamp III) which grips one end of the cross'shaft I06.

A ratchet case I|2, best shown in Fig. 4, turns about a shaft H3 and is connected with the crank arm I09 by a link H4. The full-line positions of the parts in Fig. 4 correspond with the neutral position of the shaft 5|. When the cam 61 is in the position shown in broken lines, the lower flank I00 of the cam pushes the plunger I03 back and causes the teeth. on the plunger to turn the gear segment I01 and move the crank arm I09, link H4 and ratchet case H2 into the positions shown in broken lines. The movement of the ratchet case amounts to ninety degrees in Fig, 4.

A pawl II 6 carried by the ratchet case 2 turns a ratchet I i1 in a counter-clockwise direction. The ratchet is connected with the stem of a rotary snap-switch II9 (Figs. 3 and 5) which requires a full quarter-turn to cause it to snap. If the ratchet case turns less than a quarterturn and then backs to neutral position, the pawl H6 and the ratchet back to their original positions without operating the switch. The details of the switch construction are not shown, rotary snap-switches being well known in the art, but Fig. 3 shows four contacts or brushes I2I, I22, I23 and I24 bearing against contact segments I25 and I26 on a rotatable disc I28 which is made of insulating material. When the switch II9 snaps, the disc I28 turns a quarter revolution. In the positions shown in Fig. 3, the contact segment I25 connects the brushes IZI and I24, and the segment I26 connects the brushes I22 and I23, but when the disc has moved ninety degrees the segments on the disc connect brushes I2I and E22 and connect brushes I23 and I24. Another quarter turn connects the same brushes as shown in the drawings. The switch II9 operates as a phase-changing or polarity-changing switch.

Fig. 6 is a wiring diagram showing the control circuits of the three-phase motor 24. This motor has three terminals l3I, I32 and I33. The terminal I3I is connected directly with the power line. Each of the other motor terminals is connected with two of the stationary contacts on opposite sides of the frame 80. The contact plates I9 and 39 are connected with brushes I23 and I2I, respectively. The other brushes I22 and I24 connect directly with the power line.

Fig. 5 is a sectional view looking from a plane near one end of the switch box 52. This view shows a panel I40 with fuse clips I4I, I42 and I43 and connections to the motor and switch conductors. A fuse I45 is shown in each clip. Conductors lead from each of the fuse clips to a polarized connection I41 for an extension cord.

The operation of the jack will be reviewed briefly. When the control handle 54 is in the neutral position shown in Fig. 1, the switch arm 59 (Fig. 2) and the other switch arm I0 immediately behind it are in a neutral position between the contacts 82, 83, 92 and 93 (Fig. 6) and no power is supplied to the motor. The brake remains set, so that if the jack is raised and under load the weight of the load can not turn the operating mechanism. and lower the jack.

When the control lever is pushed up, it turns the shaft 5I (Fig. 3) clockwise and brings the recess 95 into line with the plunger I03 so that the pressure of the plunger will hold the shaft 5| and its connected parts in their new position. In this position the switch arm 69 holds the contact 16 against the fixed contact 82 and the other switch arm holds the contacts 86 and 92 (Fig. 6) together. There is then a circuit from the terminal I32 of the motor through contacts 82, I6

and. I! to plate I9, and from this plate through brush I23, segment I26 and brush I22 to the Dower line. The terminal I33 of the motor connects with the power line through contacts 92, 86, 8?, plate 89, brush I2I, segment I25, and brush I24.

If these circuits cause the motor to rotate in a direction to raise the jack, then the ram will rise until the control lever is manually shifted to neutral position or until the abutment 6| (Fig. 1) on the lower portion of the jack strikes the block 56, lifts the link 65 and crank 40 so that the shaft 5| is turned back to neutral position. If these circuits cause the motor to rotate in a direction to lower the jack and the ram is already near its lowest position, then the upper abutment will push the block 56 down and cause the shaft Hi to turn clockwise beyond its normal "up" position.

The effect of this abnormal movement is shown in Fig. 4. As the shaft 5| and cam 61 turn clockwise, the flank I00 thrusts the plunger I03 further and further back and causes the gear segment I01 to turn and rock the crank I09 into the broken-line position shown. By the time the crank I09 reaches this position, the ratchet cage H2 has made a quarter revolution and caused the switch to snap into a position in which the segment I25 (Fig. 6) connects contacts I2I and i222, and a circuit between contacts I23 and I24 is closed by the segment I26. The change in the positions of the segments I25 and I26 connects the motor terminals I 32 and I33 with different wires of the power line and effects a reversal of the motor.

In the event that the motor turns in the wrong direction when the control lever is moved to its down position, the shaft 5| (Fig. 4) is turned counter-clockwise until the flank IOI of the cam 6'. pushes the plunger I03 back and effects a reversal of the motor in the same way as when the cam turns into the broken-line position already explained. The phase-changing switch II 9 can be manually operated by moving the control handle 54 (Fig. 1) far enough to turn the shaft 5| and cam 61 (Fig. 4) into the position shown in broken lines or the corresponding position on the opposite side.

The preferred embodiment of the invention has been described, but changes and modifications can be made, and some features of the invention can be used without others.

I claim:

1. A lifting jack including an electric motor and mechanism operated by the motor to raise or lower the jack depending upon the direction of rotation of the motor, switch means controlling the supply of power to the motor, and a control lever which causes the motor circuit to be open when said lever is in a neutral position, and switch means in the motor circuit which cause the motor to operate in opposite directions when the lever is shifted to opposite sides of said neutral position, and which reverse the motor if shifted further in the same direction.

2. The improvement in electric motor-operated lifting jacks which comprises switch means controlling the supply of power and the direction of operation of the motor, and a switch-operating member movable to either side of a neutral position to cause the motor to operate in one direction or the other, and connections effective to reverse the motor upon further movement of said member in either direction away from the neutral position.

3. The combination with a lifting jack having an electric motor, of two reversing switches connected in the circuit of said motor in such a manner that shifting of either switch changes the direction of operation of the motor, a switch operating member which operates one of said switches when moved to either side of a neutral position, and means actuated by said member to operate the other switch when the operating member is moved to either side of its neutral position for a distance substantially greater than necessary to operate the first switch.

4. The combination with a lifting jack having a reversible electric motor, of two switches in the motor circuit including a first switch that has an open position but closes in either direction frnrn said open position to cause rotation of the motor one way or the other, and a snap-switch effective to change the direction of rotation of the motor, a switch operating lever for the first switch, and connections actuated by said lever to operate the snap-switch when said lever moves in either direction for a substantial distance further than necessary to close the first switch.

5. In a lifting jack having a three-phase motor. a switch for shutting off the power supply to the motor, circuits that cause operation of the motor in difierent directions when the switch is closed on opposite sides of the neutral position, and a phase-changing switch in the motor circuit and operable to change the direction of movement of the motor while the first switch remains closed on either side of its neutral position.

6. A lifting jack comprising a ram, operating mechanism for said ram including an electric motor, a switch controlling the supply of power and the direction of operation of the motor, a switch-operating handle movable to opposite sides of a neutral position to operate the switch to start the motor in one direction or the other,

a second reversing switch in the motor circuit, 1;

the handle operates said switches.

7. In an electrically-operated lifting jack, a ram, automatic stop means for stopping further movement of the ram when it reaches certain positions nearrthe upper and lower limits of its travel, and automatic reversing means for preventing further movement of the ram beyond said stop positions in the event that said automatic stop means fail to stop the ram.

8. In alifting jack having an electric motor and automatic stop means for opening the motor circuit when the ram reaches predetermined limits of travel in either direction, the improvement of a reversing switch in the motor circuit, and means efiective to operate said reversing switch if the automatic stop means fail to halt the movement of the ram at said predetermined limits.

9. In a lifting jack having a ram and operating mechanism driven by a three-phase motor, means actuated by the operating mechanism for opening the motor circuit as the ram approaches its upward limit of travel, means actuated by the operating mechanism for opening the motor circuit as the ram approaches its downward limit of travel, and apparatus operated by the jack-operating mechanism to interchange the circuits of the limit means when the motor operates in the wrong direction to make said limit means effective.

10. The combination with a lifting jack having operating mechanism driven by an electric motor, of a control circuit'with automatic limit switch means for stopping the operating mechanism at predetermined positions in the upward and downward movement of the jack, and other automatic switch means which change the control circuit if the motor operatesin a direction that makes the limit switch means ineffective.

v 11. A lifting jack comprising a ram and operating mechanism for the ram including an electric motor, switches in the motor circuit including a limit switch actuated by the operating mechanism as the ram reaches its normal a ram operated by limit of travel, and another switch actuated by the operating mechanism when the ram moves beyond its normal limit of travel.

12. A lifting jack including a ram, operating mechanism for the ram, an electric motor that drives said operating mechanism, a switch that opens the motor circuit when said switch is in neutral position and closes a circuit which causes the motor to operate in one direction or the other when moved to either side of neutral position, abutments connected with the ram, a block connected with the switch and located in the path of the abutments, and a second switch operated by said abutments to change the circuits of the first switch if said abutments move the block in the wrong direction to stop the motor.

13. In a portable lifting jack having a threephase electric motor and an extension cord for connecting the motor with a source of power, the combination of a limit switch and an abutment which shifts the limit switch to stop the motor when the jack approaches its limit of travel in one direction, and .a phase-changing switch operated by movement of the limit switch in the wrong direction by said abutment.

14. In a lifting jack including an electric motor and mechanismoperated by the motor, a control handle movable into three positions, a switch operated by said handle to open the circuit when the handle is in mid-position and to cause the motor to operate in opposite directions when shifted to either side of mid-position, a mechanical brake for holding the mechanism against movement when the switch is in open position and the motor is not energized, and connections through which the brake is controlled by the same handle that operates the switch, said connections being effective to release the brake before the switch closes in either direction.

15. In a lifting jack operated by an electric motor, a control-switch movable to either side of an open, neutral position to cause operation of the motor in either direction, a polaritychanging switch in the motor circuit, a brake for stopping the motor and holding it against rotation when the motor circuit through the switches is open and there is nopower in the motor, and a common control handle that operates both of the switches and said brake.

KARL ECK.

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