US3306997A

US3306997A - Limit switch control for a motor drive

Info

Publication number: US3306997A
Application number: US453587A
Authority: US
Inventors: David R Jacobs
Original assignee: Franklin Electric Co Inc
Current assignee: Franklin Electric Co Inc
Priority date: 1965-05-06
Filing date: 1965-05-06
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28

Description

Feb. 28, 1967 D. R. JACOBS 3,306,997

LIMIT SWITCH CONTRL FOR A MOTOR DRIVE Filed May 6, 1965 @Mik/1 9W United States Patent O 3,306,997 LIMIT SWITCH CNTROL FOR A MUTOR DRIVE David R. Jacobs, Bluffton, Ind., assigner to Franklin Electric Co., Inc., Bluffton, Ind., a corporation of Indiana Filed May 6, 1965, Ser. No. 453,587 12 Claims. (Cl. 20D-47) This invention relates to motor drive units, and more particularly to a limit switch control for a motor drive unit.

A motor drive unit of the type designed to be connected to move a member between two positions, such as a motor drive unit for raising and lowering a garage door, requires limit switches which are responsive to the arrival of the member at the `two limits of movement of the member to turn off the motor drive unit. In a garage door opener, for example, the limit switches are connected to turn ofi the drive unit both when the door is all the way up and is all the way down.

It is a principal object of this invention to provide a limit switch control for a motor drive unit, which may be easily and accurately adjusted to turn off the motor drive unit at precisely the desired positions of the member being driven.

lt is another object of the invention to provide a limit switch control of the foregoing character, which will not easily fall out of adjustment.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying figures of the drawing, in which:

FIG. l is a perspective view of a motor drive unit including a limit switch control constructed in accordance with the invention;

FIG. 2 is an enlarged view showing the limit switch control;

FIG. 3 is an exploded perspective view of the limit switch control;

FIG. 4 is a view showing a portion of the limit switch control;

FIG. 5 is a view similar to FIG. 4 but showing the portion of the limit switch control during adjustment; and

FIG. 6 is an enlarged fragmentary sectional view taken on the line 6 6 of FIG. 2.

Briey, a limit switch control embodying the invention is designed to control the extent of rotation in both directions of a motor drive unit having a rotating power output shaft. The limit switch control includes a cam drive shaft connected to the power output shaft for rotation therewith7 and a limit shaft rotatably mounted adjacent the cam drive shaft. Two cam members are positioned on the limit shaft, one of the cam members being secured to the limit shaft for rotation therewith and the other of the cam members being loose on the limit shaft. The latter cam member is connected by a gear arrangement to be rotated by the cam drive shaft. The two cam members are connected together by a clutch arrangement including a plurality of radially extending teeth on engageable surfaces of the two cam members, and the two cam members are spring urged toward each other. When the two cam members are clutched together, rotation of the cam drive shaft produces rotation of the two cam members and the limit shaft, and the construction is such that numerous revolutions of the cam drive shaft are required to cause one revolution of the limit shaft.

The limit switch control further includes a pair of limit switches, one of the limit switches being connected to turn ofr the motor drive unit when the limit of rotation in one direction has been reached, and the other limit switch being connected to turn olf the motor drive unit when the limit of rotation in the other direction has been reached. A cam surface is formed on each of the two 3,3%,997 Patented Feb. 2S, 1967 cam members, and the limit switches are positioned to be actuated lby the cam surfaces upon rotation of the cam drive shaft.

To adjust the number of revolutions of the cam drive shaft, in one direction required to turn olf the motor, which corresponds to the position of the driven member at which the motor drive unit will be turned oli', one of the two cam members may be adjusted relative to the other of the cam members. This is accomplished by applying a rotative force on the limit shaft. The cam member which is connected to the cam drive shaft through the gear connection, and is loose on the limit shaft, will remain angularly stationary while the other of the cam members, which is secured to the limit shaft, will turn with the limit shaft. The ridges formed by the teeth of the clutch connection urge the two cam members slightly apart against the action of the spring and a click may be heard as the teeth of the clutch pass each other and snap back together. The number of teeth of the clutch is preferably related to a one-to-one ratio to the gear ratio between the cam drive shaft and the limit shaft, and therefore one click of the clutch teeth represents one revolution of the power output drive shaft. Consequently, the extent of rotation of the powerv output shaft may easily ybe adjusted by rst noting the increase or decrease in the number of revolutions of the power output shaft desired, and then turning the limit shaft until a corresponding number of clicks are heard.

Since a large number of radially extending teeth may be provided in the clutch, a very large number of possible angular positions of one cam member relative to the other cam member may be obtained, and the limit shaft is made easily accessible for adjustment. Further,

vimproved results are obtained by the loose mounting on the limit shaft of the cam member which is engaged by the cam drive shaft, while the other of the cam members is rigidly secured to the shaft, because rotation of the cam drive shaft and the motor unit is not necessary when making an adjustment.

In greater detail, in FIG. l is shown a motor, indicated -by the numeral 1l), having a rotor shaft (not shown). The rotor shaft is connected through a gear box 11 to a cam drive shaft 12, which may be an extension of the power output shaft of the motor-gear box unit or a shaft connected to be rotated by the power output shaft. Fastened to the side of the gear box 11 is a limit switch control 14 which is fastened to the gear box 11 as by a plurality of bolts 16.

With reference to FIG. 2, the limit switch control 14 comprises a housing 17 having a plurality of holes 18 formed therethrough for the bolts 16. A cover 19 for the housing is also provided, the bolts 16 extending through holes formed in the cover and securing the cover 19 to the housing as well as securing the housing to the box 11. Mounted within the housing 17 are two

electric limit switches

21 and 22 having

terminals

23 and 24, respectively. Conductors 25 are secured to the terminals for making electrical connction with an external power circuit (not shown). The conductors 25 extending through a hole 20 in the housing 17. The limit switch control 14 also further includes a limit shaft 26 which is journaled at its ends in two holes 27 and 28 (FIGS. 2 and 6) formed in the housing 17. With reference to FIG. 3, a circumferential groove 29 is formed in the shaft at the hole 28, and a pin 31 is secured to the housing and extends into the groove 29 to prevent substantial axial movement of the limit shaft 26 in the housing 17.

Mounted on the limit shaft 26 are an adjustable face cam member 33 and a lfixed face cam member 34, the former cam member 33 being secured to the limit shaft 26, as by knurling a portion 30 of the surface of the

shaft f buttons

53 and 54 opens the 26 and pressing the member 33 on the knurled portion, and the latter cam member 34 being loosely mounted on the limit shaft 26. A compression spring 36 is positioned around the limit shaft 26 between the cam member 34 and a snap ring 35, and urges the fixed cam member 34 toward the adjustable cam member 33. The snap ring 35 is positioned around the shaft 26 in a groove 35a formed in the shaft 26, and a washer 35h is positioned between the other end of the spring 36 and the cam member 34. When the terms xed and adjustable are used herein with regard to the two

cam members

33 and 34, it is meant that the cam member 33 is adjustable in the rotary direction with the shaft 26 but is substantially stationary in the axial direction, while the cam member34 is axially movable relative to the shaft 26.

One end of the cam drive shaft 12 extends into the limit switch control housing 17 adjacent the cam member 34, and this end of the shaft 12 has a worm 37 formed on it. The cam member 34 is cylindrical and its outer surface has axially extending gear teeth 38 formed on it, which mesh with the worm 37 of the shaft 12. Therefore, rotation of the cam drive shaft 12 also causes rotary movement of the cam member 34.

The two

cam members

33 and 34 are adjustably connected together by a clutch arrangement including similar sets of V-shaped radially extending

clutch teeth

41 and 42 formed on the

cam members

33 and 34, respectively. The

members

33 and 34 may, for-example, be molded plastic members. The cam member 34 is shown as having an annular llange 43 (FIG. 4) at its outer periphery, the flange 43 extending around an annular axially extending ange 44 formed on the cam member 33. The adjacent surfaces of the flanges 43 and 44 act as a guide during movement of the cam member 34 relative to the cam member 33. The

clutch teeth

41 and 42 are formed on the outer -radially extending surface of the flange 44 and on an adjacent radially extending surface of the cam member 34. The

members

33 and 34 are also provided with hubs 46 and 47, respectively, which engage the shaft 26, and the interior of the

members

33 and 34 may be recessed between the surfaces having the

teeth

41 and 42, and the hubs 46 and 47.

The spring 36 urges the cam members together and tends to hold the

teeth

41 and 42 in engagement. When the

teeth

41 and 42 are engaged as shown in FIGS. 2 and 4, rotation of the cam drive shaft 12 causes rotation of the cam member 34 due to the connection between the worm 37 and gear teeth 38, and the clutch connection, including the sets of

teeth

41 and 42, imparts motion from the cam member 34 to the cam member 33 and the limit shaft 26.

The two

cam members

33 and 34 are respectively provided with raised

cam surfaces

51 and 52 on their radial sides which are away from the

teeth

41 and 42. The

limit switches

21 and 22 are provided with depressible actuating

buttons

53 and 54, respectively, and the

limit switches

21 and 22 are positioned such that the

cam surfaces

52 and 51 are engageable with the two buttons 53 and S4. Upon rotation of the limit shaft 26 and the two

cam members

33 and 34 in one direction, the cam surface 52 engages the button 53 and actuates the limit switch 21, and upon rotation of the limit shaft 26 in the opposite direction, the cam surface 51 engages the button 54 and actuates the other switch 22, The drive motor 10 is connected in a conventional manner to be energized through the

switches

21 and 22, and depression of the

switches

21 and 22. Therefore, if the drive motor is energized for rotation in one direction, energization will continue until the cam member 52 engages the button 53 and actuates the limit switch 21 to turn off the motor. Energization of the motor 10 in the opposite direction rotates the limit shaft 26 and the two cam members in the opposite direction until the raised cam surface 51 engages the button 54 of the other limit switch 22 and again deenergizes the motor 10. v

It will be apparent that the number of revolutions of the motor 10 required to go from one limit to the other, depends upon the gear ratio between the worm 37 and the gear 38 teeth.

The construction of the

teeth

41 and 42 of the clutch, and the construction of the worm 37 and gear 38 teeth are preferably such that the angular separation between adjacent teeth of each set of

teeth

41 and 42, is equal to the angular displacement of the two

cam members

33 and 34 due to one complete revolution drive shaft 12. Therefore, when adjusting the position of Ithe cam member 33 relative to the cam member 34, the number of revolutions of the drive shaft 12 to be increased or decreased is determined and the two

cam members

33 and 34 are then angularly displaced a corresponding number of

clutch teeth

41 and 42.

To aid in ease of adjustment of one of the cam members relative to the other of the cam members, the ends of the limit shaft 26 are provided with slots 56 which may be engaged by a screw driver from outside lthe housing 17 of the limit switch control. As previously stated, holes 27 and 2S are formed in the housing 17, and the ends of the shaft 26 are mounted in the

holes

27 and 28 with the slots 56 appearing at the outer ends of the holes so that the slots 56 may be engaged by a screwdriver externally of the housing 17.

To explain the operation of the unit, assume that the unit has its power output shaft connected to raise or lower a garage door, for example. The power output shaft may ybe connected to the door such that the switch 22 is actuated by the cam S1 when the garage door reaches the upper position. To adjust the lower position of the garage door at which the motor 10 will be deenergized, the llrst step may be to determine the distance of travel of the garage door caused by one revolution of the drive shaft 12. Then, the total number of revolutions of the shaft 12 to provide the desired adjustment may be determined. If it is decided, for example, that an adjustment equalling three revolutions of the shaft 12 is required, a screw driver is inserted into one of the slots 56 and rotary force is applied to turn the shaft 26 in one direction or the other, depending upon whether it is desired to increase or decrease the height of the garage door at which the motor 10 is to be turned off. Since the shaft 26 and the cam member 33 are axially stationary, except for slight movement due to play between the pin 31 and the sides of the groove 29, and the cam member 34 is held against substantial rotation due to the engagement of the gear teeth 38 with the worm 37, the rotary force applied to the shaft 26 causes the cam member 34 to move axially away from the other cam member 33 as the

teeth

41 and 42 pass each other. The fact that the gear teeth 38 extend axially and that the outer surfaces of the member 34, having the teeth 38 formed thereon is flat, enables the member 34 to move axially without interference due to the engagement of the teeth 38 with the worm 37. FIG. 5 shows the two cam mem-bers separated by an amount which is substantially more than would occur during operation, and is intended to further illustrate the construction of the cam members. The ridges formed by the

teeth

41 and 42 urge the two

cam members

33 and 34 apart against the action of the spring 36, and a click will usually be heard as the teeth pass each other and reengage. Furthermore, since the angular distance between the

teeth

41 and 42 is related in a one-to-one ratio with the gear ratio between the worm 37 and the gear teeth 38, rotation of the shaft 26 sutlcient to cause 3 clicks will result in an adjustment equivalent to three complete revolutions of the shaft 12. Even if a click cannot be heard, the action of the teeth passing each other may be felt through the screw driver. As soon .as the rotative force applied to the limit shaft 26 is removed, the

teeth

41 and 42 will be held in mutual engagement by the force of the spring 36.

The limit switch control described has numerous advantages. For example, the relative positions of the two

cam members

33 and 34 may be easily adjusted from outside the housing 17 of the control unit, making it unnecessary to remove the cover 19 in order to make an adjustment. Furthermore, an adjustment may be made either with or without power applied to the motor Still further, an accurate adjustment may Ibe made because of the relationship between the

teeth

41 and 42, and the gear ratio between the worm 37 and the gear teeth 38, which produces one click for each revolution of the cam drive shaft 12. Still another .advantage of the construction is that a setting of the limit switch control is positive and relatively permanent. In other words, it is not easily changed by accident. Also, the limit switch setting will not be changed by vibration of the unit, by manual turning of the power output shaft of the motor unit, or through a careless adjustment of the unit.

I claim:

1. A limit switch control for a motor drive unit, comprising a rotatably mounted limit shaft, a pair of cam members on said limit shaft, a pair of limit switches positioned adjacent said members and adapted to be actuated by the respective cam members on rotation of the latter, one of said cam members being secured to said limit shaft for rotation therewith, one of said cam members including a worm wheel, a worm for driving said worm wheel, said cam members having adjacent end faces provided with interengaging teeth, and spring means tending to move one of said cam members axially toward the other to effect engagement of said teeth, said limit shaft having means on at least one end thereof for engagement by a tool for rotating said limit shaft, said teeth being formed to cam said cam members apart on rotation of said limit shaft by said tool and said spring means causing said teeth to produce an audible click when the teeth on the respective cam members pass each other, the number of teeth on said cam members having a predetermined relation to the rotation of said worm, whereby the number of clicks indicates the amount of adjustment of said worm.

2. Apparatus as in claim 1, wherein said one cam member which includes a worm wheel is axially and rotatably movable on said limit shaft, and said spring means comprises a compression spring which is positioned around said limit shaft, one end of said spring being axially stationary relative to said shaft and the other end of said spring operably engaging said cam member which includes said worm wheel.

3. Apparatus as in claim 1, and further including a housing for said control, said limit shaft being rotatably mounted in said housing, said housing having an opening formed therein, and said end of said limit shaft which is engageable by a tool being accessible through said opening, whereby said adjustment may be made without the necessity of opening up said housing.

4. Apparatus as in claim 1, wherein said one cam member including a worm wheel is moved axially away from the other of said cam members as said teeth cam said cam members apart.

5. Apparatus as in claim 1, wherein said one cam member including a worm wheel is cylindrical, and the worm wheel includes axially extending teeth formed on the outer periphery of said one cam member.

6. Apparatus as in claim 1, wherein said cam members have generally cylindrical, axially extending guide surfaces formed thereon, said guide surfaces being mutually engageable and guiding the relative axial movement of said cam members.

7. Apparatus as in claim 1 and further including a housing for said limit switch control, said housing having holes formed therein and the ends of said limit shaft being rotatably positioned in said holes, and means for preventing substantial axial movement of said limit shaft relative to said housing, comprising an annular groove formed in said limit shaft, and a pin secured to said housing and extending into said groove.

3. A limit switch control for a motor drive unit including :a rotatable power output shaft, comprising a limit shaft, a pair of cam members on said limit shaft, a pair of limit switches positioned adjacent said cam members and adapted to be actuated by the respective cam members on rotation of the latter, one of said cam members being secured to said limit shaft for rotation therewith and the other of said cam members being loosely mounted on said limit shaft, means for connecting said limit shaft to said power output shaft for rotation thereby, said cam members having adjacent faces provided with interengaging clutch teeth, and biasing means tending to move said cam members toward each other to effect engagement of said teeth, said limit shaft having means on at least one end thereof for engagement by a tool for rotating said limit shaft, said connecting means being operable to hold the cam member which is loose on the limit shaft against rotation when said limit shaft is rotated by said tool, said teeth being formed to cam said cam members apart on rotation of said limit shaft by said tool, and said biasing means causing said teeth to produce an audible click when said teeth on the respective cam members pass each other, the number of teeth on said cam members having a predetermined relation to the rotation of the power output shaft, whereby the number of clicks indicates the adjustment of the point at which the limit switch associated with the cam member secured to said limit shaft will be actuated.

9. A limit switch control for a motor drive unit including a rotatable power output shaft, comprising a pair of cam members, a pair of limit switch members, each of said switch members being associated with one of said cam members, means for rotatably mounting one of said pairs relative to the other of said pairs, said limit switch members being located adjacent the cam members and being actuated by the respective cam members on relative rotation of said one pair, means adapted to connect one of said members of said one pair to the power output shaft for rotation of said one member in timed relation with said power output shaft, said members of said one pair being rotatably and axially movable relative to each other, and clutch means for connecting said members of said one pair, said clutch means including a set of clutch teeth on each of said members of said one pair, said teeth extending substantially radially of the axis of rotation of said one pair, and means for biasing said members toward each other to move said sets of teeth into engagement, said connecting means comprising a worm and gear construction, said worm being rotatable on rotation of said power output shaft and said gear being rigid with said one member of said one pair, and the angular separation of said clutch teeth being substantially equal to the angular distance said gear travels due to one complete revolution of said worm.

10. Apparatus as in claim 9, wherein said rotatably mounted pair comprises said pair of cam members.

11. Apparatus as in claim 9, wherein said means for rotatably mounting one of said pairs comprises a limit shaft, and means for rotatably mounting said limit shaft, one of said members of said one pair being secured to said limit shaft and the other of said members of said one pair being loosely mounted on said limit shaft.

12. A limit switch control for a motor drive unit including a rotatable power output shaft, comprising a pair of cam members, a pair of limit switch members, each of said switch members being associated with one of said cam members, means for rotatably mounting one of said pairs relative to the other of said pairs, said limit switch members being actuated by the respective cam members on relative rotation of said one pair, means adapted to connect one of said members of said one pair to the power output shaft for rotation of said one member in timed relation with said power output shaft, said members of said one pair -being rotatably and axially movable relative to each other, and clutch means for connecting said members of said one pair, said clutch means including a set of clutch teeth on each of said members of said one pair, said teeth extending substantially radially of the axis of rotation of said one pair, means for biasing said members toward each other to move said sets of teeth into engagement, said means for rotatably mounting one of said pairs comprising a limit shaft, and means for rotatably mounting said limit shaft, one of said members of said one pair being secured to said limit shaft and the other of said members of said one pair being loosely mounted on said limit shaft, a housing for said members and said limit shaft, a cover for said housing, and at least one end of said limit shaft having means formed thereon for engagement by a tool. said limit shaft being mounted in said housing with said one end accessible from outside said housing, whereby an adjustment may be made without the necessity of removing said cover.

References Cited by the Examiner UNITED STATES PATENTS 2,468,974 5/1949 Hammer 200--153 X 2,711,450 6/1955 Carr 20G-153 X 2,876,313 3/1959 Dull et al. ZOO-153 3,l75,4l8 3/1965 Schaefer ZOO-47 X BERNARD A. GILHEANY, Primary Examiner.

T. MACBLAIN, Assistant Examiner.

Claims

1. A LIMIT SWITCH CONTROL FOR A MOTOR DRIVE UNIT, COMPRISING A ROTATABLY MOUNTED LIMIT SHAFT, A PAIR OF CAM MEMBERS ON SAID LIMIT SHAFT, A PAIR OF LIMIT SWITCHES POSITIONED ADJACENT SAID MEMBERS AND ADAPTED TO BE ACTUATED BY THE RESPECTIVE CAM MEMBERS ON ROTATION OF THE LATTER, ONE OF SAID CAM MEMBERS BEING SECURED TO SAID LIMIT SHAFT FOR ROTATION THEREWITH, ONE OF SAID CAM MEMBERS INCLUDING A WORM WHEEL, A WORM FOR DRIVING SAID WORM WHEEL, SAID CAM MEMBERS HAVING ADJACENT END FACES PROVIDED WITH INTERENGAGING TEETH, AND SPRING MEANS TENDING TO MOVE ONE OF SAID CAM MEMBERS AXIALLY TOWARD THE OTHER TO EFFECT ENGAGEMENT OF SAID TEETH, SAID