US3549833A - Actuators - Google Patents

Description

United States Patent Inventor Peter Horton Luton, England Appl. No. 753,648 Filed Aug. 19, 1968 Patented Dec. 22, 1970 Assignee The English Electric Company Limited London, England aBritish company Priority Aug. 18, 1967 Great Britain 387288/6 ACTUATORS 11 Claims, 7 Drawing Figs.

US. 200/47, 192/142, 192/150 Int. Cl. ll0lh 21/28 Field of Search 200/47;

Attorneys-Misegades & Douglas, Keith Misegades and George R. Douglas, Jr.

ABSTRACT: This invention concerns a. switch mechanism for a rotary actuator. The mechanism includes a first rotary member which is driven by the output shaft of the actuator and which drives through a reduction gear a second rotary member mounted in a pivoted housing which swings about its pivot axis against a spring action and operates a switch when, after rotation of the second rotary member to a predetermined position, an abutment on the second rotary member engages a second abutment (preferably on the first rotary member) which stops further rotation of the second rotary member which instead then moves bodily and swings the housing about its pivot axis to operate the switch.

ACTUATORS This invention relates to switch mechanisms for rotary actuators, and particularly for actuators powered by electric motors.

A switch mechanism according to this invention includes a first rotary member which is to be driven by the output shaft of the actuator and which drivesthrough a reduction gear a second rotary member mounted in a pivoted housing which swings about its pivot axis against a spring action and operates a switch when, after rotation of thesecond rotary member to a predetermined position, an abutment on the second rotary member engages a second abutment which stops further rotation of the second rotary member whichinstead then moves bodily and swings the housing about its pivot axis to operate the switch. I

Preferably the second abutment is on a member which rotates with the first rotary member. Alternatively, however, the second abutment may be fixed to thehousing.

The switch operated by the pivoted housing when the second rotary member engages the stop maybe arranged to switch off the actuator motor. In practice there may be two switches arranged to operate for opposite directions of rotation of the actuator output shaft, at positions of the second rotary member corresponding, for example, to the closed and open positions of a valve controlled by the actuator; the output shaft of the actuator may, for example, drive a nut which is screwed around a threaded axially moving spindle controlling the valve. t

Two embodiments of this invention will now be described by way of example with reference to the accompanying drawings of which: i

FIG. 1 is a sectional side elevation of one embodiment of a switch mechanism for a rotaryactuator;

FIG. 2 is a sectional view along the line II-ll of FIG. 1;

FIG. 3 is a view in the direction of arrow A of a detail of FIG. 1;

FIG. 4 is an end view in the direction of arrow B of FIG. 1;

FIG. 5 is a sectional side elevation of a second embodiment of a switch mechanism for a rotary actuator;

FIG. 6 is a sectional view along the line VI-VI of FIG. 5; and FIG. 7 is a sectional view along the line VII-VII of FIG. 5 showing a detail of the embodiment of FIG. 5.

Referring to the drawings, FIGS, 1 to .4 illustrate one embodiment of a switch mechanism for arotary actuator the switch mechanismbeing housedin a cup-shaped casing 10.

i The switch mechanism has a support. structure 11 which comprises a backplate 12 supported from themain body of the rotary actuator by support means not shown) and a tubular bearing member 13 which is secured to the backplate 12 and extends substantially perpendicular to the backplate 12, with its axis substantially parallel to the longitudinal axis of the casing 10. The tubular bearing member 13 supports a shaft 14 which serves as the first rotary member of the basic construc tion according to this invention. End portions 15 and 16 of the shaft 14 protrude from opposite ends of the tubular bearing member 13. a

An input shaft 17, which is rotatably-driven about its own axis by the output shaft (not shown) of the rotary actuator, extends into the casing 10. This inputshaft 17 carries a gear wheel 20 which meshes with a gear wheel 21 of a friction drive mechanism 22 through which the gear'wheel 21 drives the shaft 14. A stop 18 is screwed into a'hole 19 in the backplate 12 and-bearsagainst the adjacent face'ofthe gear wheel 20.

The friction drive mechanism 22 includes a collar 23, which is mounted on theshaft portion 16, a spring washer 24 and an annular member 25 which is secured to the shaft portion 16. The spring washer 24 bears between the collar 23 and the gear wheel 21 and loads the gear wheel 21 into frictional engagement with the annular member 25, sothat rotation of the gear wheel 21 causes rotation of the annular member 25 and thus causes a rotation of the shaft 14. It will be seen that the gear wheel 21 is free to rotate with respect to the shaft 14 in the event of the clutch slipping owing tothe shaft 14 being jammed or for any other reason.

Two switch units 26, 27 are mounted on opposite sides of the tubular bearing member 13. Each switch unit 26, 27 comprises a bank of four microswitches 28 mounted side-by-side between two end plates 29, 30. Each microswitch has an actuating probe 31 (see FIG. 2) by which it is operated. The end plates 30 of each switch unit 26, 27 are mounted flush with the surface of the backplate 12 remote from the friction drive mechanism 22, so that the switch units 26, 27 extend in a direction substantially perpendicular to the surface of the backplate 12. Each switch unit 26, 27 is pivotally supported by a setscrew 32, 33 (see FIG. 2) which passes through holes near the bottom edges of the end plates-29, 30, below the switches 28, and is screwed into the backplate 12. A tension spring 34 (FIG. 1) which is connected between the top parts of the end plates 29, above the switches 28, loads the switch units 26, 27 towards each other. A stop member 35 is mounted on the tubular bearing member 13 between theswitch units 26, 27 to ensure that the switch units 26, 27 are spaced apart from each other by the required minimum distance.

In accordance with this invention, there is a pivoted housing which comprises a rocker member 36 mounted on the end portion 15 of the shaft 14 so that it is free to pivot about the axis of the shaft 14. The rocker member 36 comprises a beam element 37, a central leg portion 38 and an end leg portion 39. The shaft portion 15 passes throughthe leg portions 38 and 39 which support the beam element 37 at a" spaced distance from the shaft 14. The beam element 37 lies parallel to the shaft 14 and has an extension 40 extending towards the backplate l2 and lying between the actuating probes 31 of the switch units 26, 27. The width of an end part 41' of the part 40 lying between the two microswitches 28 nearest to the backplate 12 is less than the width of the remainder of the part 40.

The shaft portion 15 carries a worm element 42 which is securely fixed to the shaft portion 15 so as to rotate with-the shaft 14. The worm element 42 carries two collars 43 and 44, one at each endof the worm element 42. Each collar 43, 44 carries a radially extending pin 45, 46 and is securely fixed to the worm element 42 so as to rotate with the shaft 14. The lengths of the radially extending pins 45, 46 are such that they do not foul the portion 47 of the beam element 37 extending between the leg portions 38, 39 as the disc members 43 and'44 rotate. The collars 43, 44 are adjustable as to their angular positions relative to the worm element 42.

The beam portion 47 is formed with a longitudinally extending slot 48 above the worm element 42. This slot contains a worm wheel 50, mounted on a pin 49, which meshes with the worm on the shaft 14. The worm wheel is secured to'the pin 49. Two discs 51 (only one of which is shown in FIG. 1), which each serve as a second rotary member in accordance with this invention, are also secured to the pin at opposite ends so as to lie on opposite sides of the beam portion 47. Each disc 51 carries a radially extending pin 52 of such length that it can be engaged by one of the radially extending pins 45 or 46 on the worm element. In other words, in theterms of this invention, each pin 52 serves as a first abutment while each pin 45, 46 serves as a second abutment. The discs 51 are adjustable as to their angular positions on the pin 49..

A peg 53 protrudes from the outer face of the end leg portion 39 of the rocket member and is capable of engaging in a hole in a member 54 which is secured to the end of a shaft 55 which protrudes through and is rotatably supported in the base of the casing 10. FIG. 1 shows the peg 53 disengaged. The member 54 is spring-loaded towards the rocker member 36 by a compression spring 54A and is provided with a selfcentering device which may comprise a radially extending tension spring 55A connected between an anchor screw 56A and a point on the periphery of the member 54 which is on the same radial line as the center of the hole in which the peg 53 is to engage. When the peg 53 is engagedin the member 54, the self-centering device biases the rocker member 36 into a position substantially midway between the two switch units 26, 27.

The end of the shaft 55 remote from the member 54 prowhich moves across a dial 57 (see FIG. 4) when the rocker member 36 swings about its pivot axis.

The switch mechanism also includes a torque-limiting device 58. A rod 59 extending from the actuator input drive shaft protrudes into the casing and carries an angle block 63 and the member 62 are pivoted to the top of the backplate 12 by a pin 65. A peg 66 on the block 63 projects upwards between the two arms 67, 68 of the member 62 and lies between the ends of two adjusting screws 69, 70 which are screwed through the arms 67, 68. The setscrew 61 is screwed into one side of the member 62 and is biassed into the slot in the angle member 60 by a tension spring 71 which is connected to a suitable point on the casing 10.

-A generally U-shaped spring 64 is carried by the tubular bearing member 13 so that its free arms project upwards from the tubular bearing member 13 to opposite sides of the block 63. The arms of the spring 64 pass between the end portion 41 of the beam portion 40 and the probes 31 of the two microswitches 28 adjacent the backplate 12. The thickness of the material of the U-shaped spring 64 is substantially half the difference between the widths of the end portion 41 and the remainder of the beam portion 40.

In use, as rotation of the actuator output shaft commences, the 'shaft 14 is driven at a speed proportional to the rotational speed of the actuator output shaft by the drive shaft 17 through the friction drive mechanism 22. At this stage of operation the self-centering device holds the rocker member 36 ,in the position substantially midway between the two switch units 26, 27 so that the microswitches are not operated.

As the shaft 14 rotates, the worm element 42 and the collars 43 and 44 rotate with it. Furthermore, the shaft 14 drives the worm wheel 42 and discs 51, so that the discs 51 rotate at a speed proportional to the rotational speed of the actuator output shaft until one of the radially extending pins radially extending pins 45, 46 (depending upon the direction of rotation) engages the cooperating pin 52. When this happens, the shaft 14 forces the rocker member 36 to pivot about the shaft 14 against the action of the self-centering device. Such pivotable movement of the rocker member 36 causes the beam portion 40 to press the actuating probes 31 of the microswitches 28 of one of the switch units 26, 27 to trip the microswitches 28. When the microswitches 28 are tripped, an electrical signal is transmitted to an external contactor mechanism which stops the supply of current to the electric motor driving the rotary actuator.

Because the switch units 26, 27 are pivotably mounted on the screws 32 and 33, they can pivot outwards with the rocker member 36, against the action of the spring 34, in the event of the rotary actuator failing to stop when the microswitches are tripped. This safeguards the switches. Moreover, the friction drive mechanism 22 will finally slip as a further safeguard. When the friction drive mechanism slips, the gear wheel 21 continues to rotate while the annular member stays stationary.

When the actuator encounters an excessive load (caused, for example, by jamming of the valve or other device controlled by the actuator), the rod 59 moves axially in one direction or the other and operates the torque-limiting device which trips one or other of the microswitches engaged by the U-shaped spring 64. This results in the actuator motor being stopped and prevents the motor from being overloaded.

A common form of actuator to which this switch mechanism may be applied consists basically of a worm which is driven by an electric motor and which drives a worm wheel on the output shaft of the actuator. The worm shaft is held against axial movement normally by a spring system, but moves axially against the centering spring action in the event of an excessive load (i.e., resistance against rotation) being felt by the output shaft. The rod 59 controlling the torquelimiting device of the switch mechanism may, for example, be arranged coaxially with the worm shaft of the actuator and be pressed against the end of the worm shaft so as to move axially with the worm shaft when an excessive load is placed on the actuator. The magnitude of actuator torque at which the torque-limiting device will operate to trip oneor other of the switches engaged by the spring 64 (depending upon the direction of rotation) can be adjusted bymeans of the screws 69, 70. Screwing out the screws 69, '71), so as to increase the clearance between each screw end andthe peg 66, increasing the limiting torque. FIG. 2 shows thescrews touching the peg (i.e., with zero clearance), and this setting gives the lowest limiting torque.

FIGS. 5 to 7 illustrate a second embodiment of a switch mechanism for a rotary actuator which is a modified form of the switch mechanism illustrated in FIGS. 1 to 4 and similar parts have been allocated the same reference numerals. The switch mechanism is housed in a cup-shaped casing 10 and has a support structure 11 comprising a backplate 72 supported from the main body of the rotary actuator by support means (not shown), two rods 73, 74 which are secured 'in the backplate 72 so as to extend towards the base of the casing 10, and a bearing member 75 which is mounted on the ends of the rods 73, 74 remote from the backplate 72 so as to lie substantially parallel to the backplate 72. A shaft 14 is supported for rotation within the backplate 72 and the bearing member 75. An input shaft (not shown) is rotatably driven in a similar manner to the input shaft 17 of the embodiment of FIGS. 1 to 4 and carries a gear wheel (not shown) which meshes with a gear wheel 76 which is secured to the end of the shaft 14 on the side of the backplate 72 remote from the bearing member 75 so as to rotate the shaft 14 at a speed proportional to the speed of rotation of the output shaft of the rotary actuator.

Two switch units 26, 27 are rigidly mounted on the backplate 72 and lie on opposite sides of the shaft 14. Each switch unit 26, 27 comprises a bank of four microswitches 28 mounted side by side and includes actuating probes 31.

A spacer 72A is carried by the shaft 14 between the two microswitches 28 adjacent to the backplate 72. An elongated cam member 77 of uniform cross section (shown in FIG. 6) is freely supported by the shaft 14' between the spacer 72A and the bearing member 75. The length of the cam member 77 is substantially equal to the width of three of the switches 28.

A rocker housing 78 mounted on the shaft 14 comprises two spaced support members 79 and 80 through which the shaft 14 passes, and two rods 81 and 82 which are secured with their ends in the two support members 79 and 80. The two rods 81, 82 are spaced apart from each otherfrod 81 being above and rod 82 being below the shaft 14. A gear wheel 33is secured to the shaft 14 and meshes with a gear wheel 34 which is freely rotatable about the upper rod 81 by which it is supported. The gear wheel 34 is integral with a coaxial gear wheel 85 which meshes with a further gear wheel 86 which is freely rotatable about the shaft 14. The gear wheel 86 is integral with a coaxial gear wheel 87 which meshes with a gear portion formed on a rotary member 83 which is freely rotatable on the upper rod 81. The rotary member 88 carries two spaced collars 89 and 90. Each collar 89, 90 carries an axially extending pin 91 (FIG. 7) which projects towards the support member 79, and each collar 89, 96 is secured to the rotary member 88 by a grub screw 90A (see FIG. 7) so as to rotate therewith. The collars 89, 90 are adjustable as to their angular positions relative to the rotary member 88. i

A tubular member 92 is secured to the shaft14 so as to rotate therewith. Two collars 93 and 94 are secured to the tubular shaft member 92 by grub screws 94A. The collars 93, 94 are each formed with a shoulder 95 (FIG. 7) which can engage one of the axially extending pins 91 on the collars 539, 90.

A pin 96 which is secured to the support member 80 extends towards the backplate 72 and lies in a centrally located slot 97 in the upper surface of the elongated cam member 77 (see especially FIG. 6).

Two arms 98A, 99A lie on opposite sides of the elongated cam member 77 and extend (as seen in FIG. along substans ,t'ially all the length of the elongated cam member 77. The lower endsof the arms 98A, 99Aare provided with inwardly facing grooves 100, 101 which fit around rods 73, 74 so that l the arms 98A, 99A canrpivot about the rods 73, 74.

Two further arms 98B and 99B (FIGS) lie between the respective arms 98A and 99A and the backplate 72. The arms 98B, 99B are also pivotable about the rods 73, 74 and cooperate with-the probes 31 of the two microswitches 28adjacent to the backplate 72. Means may be provided whereby pivotal movement of the arms 98A, 99A may cause similar pivotal movement of the arms 98B, 9913, whereas arms 98B, 995 may pivot without causing pivotal movement of arms 98A,99A.

A peg 53 protrudes from the-face of the part 79 of the rocker member 72 and cooperates with a member 54 in a similar manner to that been described with reference to FIGS.

1 to 4. However, in this embodiment'the self-centering device comprises two lateral tension springs103 (only one of which is 'shown in FIG. 5) connected respectively between each side of the lower end of the support memberBO and a suitable point on the casing 10.

The switch'mechanism including a torque-limiting device 58 which differs slightly from thetorque-limiting'device 58 illustrated in FIGS. 1 m4. Instead of being pivotable about the pin 65, by which it ispinned to the top of the backplate 72, the block 63 is securely fixed to a pin 65 which extends through a flange portion 72B of the backplate 72 and has its end remote from the block 63 secured to a cam member 104. The cam member 104 is free to rotate with the pin 65, and thus with the block 63, within a recess 105 in the backplate 72. The cam member 104 lies above the spacer 72A and between the upper side of the arms 98B; 998.

In use, as rotation of the actuator output shaft commences,

, the shaft 14 is driven at a speed proportional to the rotational speed of the actuator shaft through the gear wheel 76. At this stage of operation the-self-centering'device acts through the rocker member 78 and the pin 96; to hold the elongated cam member 77 in the position substantially. midway between the two switch units 26, 27 so that the microswitches 20 are not tripped.

As the shaft 14 rotates, the tubular member 92 and collars 93, 94 rotate with it. Furthermore, the shaft M drives the rotary member 88 and the collars 89, 90 through the chain of gear wheels 83, 84, 85, 86 and 87, so that the rotary member 88 rotates at a speed proportional to the rotational speed of the actuator output shaft until one of the axially extending pins 91 (depending upon the direction of rotation) reaches a position in whichit can be engaged by one of the shoulders 95 (as shown in FIG. 7). It is important to note that the collars 93, 94 rotate in theopposite direction of the collars B9, 90. Once the shoulder on one of the collars engages a pin 91, further rotation of the shaft 14 forces the rocker member 78 to pivot about the shaft 14 against the action of one of the self-centering tension springs 103. Such pivotal movement of the rocker member 78 causes rotation of the elongated cam member 77 about the shaft 14 by virtue of the circumferential movement of the pin 96 engaging in the slot 97 of the elongated cam member 77. Rotation of the elongated cam member 77 forces one of the arms 98A, 99A, to pivot about its rod 73 or 7 so that the upper end of the arm 98A, 99A depresses the actuating probes 31 of the relevant three microswitches of one of the switch units 26, 27. t

It will be appreciated that, where the means for causing pivotal movement of the arms 98B, 993 with pivotal movement of the respective arm 98A, 9A is provided, the actuating probe 31 of the remaining microswitch 28 of the switch unit 26, 27 will alsobedepressed. as a result of rotation of the elongated cam member-77. As in the. embodiment of FIGS. 1 to 4, the microswitches 28 maybe arranged to stop the rotary actuator when they are tripped. J

The arrangement is such that the lower ends of the arms 98A and 99A can move more outwards,against the actionof the spring 102, if the rocl er member continues to rotate slightly further than it should; .after the switches have been operated. This safeguard makes it possible to omit the friction drive of the previous embodiment, while the switches can be rigidly mounted. In the last resort the device is safeguarded by. the fact that the grub screws 90A, 94A havenylon't-ips' which can slip to prevent them applying an excessive driving force.

The torque-limiting device 58 operates in basically the same manner as the torque-limiting device 58 of the embodiment of FIGS. I to 4. The difference is that when; the block 63 is pivoted about the axis of the pin 65, th'epin65 rotates with it within the backplate 72, thus causing rotation of the cam member 104 within the recess .105. Rotation of the cam member 104 forces one of the arm portions 9813 or 995 to pivot about its rod 73 or 74 so that the upper end of the arm portion 08B, 99B depresses the actuating probe 31 of one of the two microswitches 28 nearest to the backplate 72 to trip that microswitch28. The cam member 104 is so shaped and positioned that it can continue rotating slightly beyond the point at which it trips the microswitch, without damaging the switch. 1 l

' Adjustment of the limiting torque can be achieved, asbefore, by screwing in or out the screws 69, 70. As shown in this example, howeventhere are leaf springs 69A, 70A which'ean engage-any one of; the six facets of the hexagonal screw heads to define six specificlimiting torque settings. As an alternative the screwheads be knurled and the springs 69A, 70A may have detent teeth engaging the screwheads and securing the screws in any positions into which they are deliberately rotated; the end faces of the screwheads may in this case be calibrated with markings indicating the different limiting torque settings represented, for example, by numerals 1 to 6.

The switch mechanism according to this invention may in general be made capable of controlling the movement of the output shaft of a rotary actuator automatically to any desired number of revolutions between, for example, one-quarter revolution and 350 revolutions in either direction, and can be made readily adjustable to suit different applications. The collars 43, 44 and the discs 51 (FIGS. 1 to 4) or the equivalent parts 92, 93, 89 and 00 in FIGS. 5 to 7 may be secured,.for example, by grub screws (not shown) so that they can be angularly adjusted, after loosening the grub screws, to adjust the range of movement of the actuator shaft at the ends of which the switches are operated to stop the actuator motor. In order to adjust the switch mechanism in any given installation, the actuator output shaft is first moved to one end of the desired travel. The parts which engage to trip the switches at that end.

of the travel are thenset into their engaging positions. Then the actuator shaft is rotated to the other end of its desired travel, and the relevant parts of the switch mechanism are then set into their engaging positions to operate the switches on the other side.

Where appropriate, the various components of the switch mechanism and the casing hereinbefore described may be conveniently made of a plastics material (e.g., nylon) although it will be appreciated that the shafts I14, I17, 49 and the rods- 73, 74, 81 and 82 are preferably made of metal (e. g., steel).

In the example shown in FIGS. 5 to 7, the bearing part may be made integral with the backplate 72, being connected by appropriate integral bridging parts. One of these bridging parts may be an extension of the flange part 723, in which case this bridging part would be formed with a curved slot through which the pin 96 canpass.

In either example an additional set of switches may beincluded to operate at various intermediate points between'the ends of travel of actuator outputThe additional switches may,

for example, be operated by a cam driven by the right-hand end of the shaft 14 via a reduction geanFor this purpose the casing would be replaced by a longer casing to house also the additional set of switches.

lclaim:

l. A switch mechanism for a rotary actuator, including first and second rotary members, a reduction gear, a pivoted housing, a spring, aswitch, a first abutment on said second rotary member and a second abutment wherein said first rotary member is driven by the output shaft of the actuator and drives through said reduction gear said second rotary member which is mounted in said pivoted housing, said pivoted housing being capable of swinging about its pivot axis against the action of said spring so as to operate said switch when, after rotationv of the second rotary member to a predetermined position, said first abutment engages said second abutment to stop further rotation of said second rotary member whereupon said second rotary member moves bodily and swings the housing about its pivot axis to operate said switch.

2. A switch mechanism according to claim 1 in which there is provided a member which is rotatable with said first rotary member and on which is mounted said second abutment.

3. A switch mechanism according to claim 2 in which the housing is pivoted about the axis of rotation of the first rotary member.

4. A switch mechanism according to claim 3 in which the axis of rotation of the second rotary member is parallel to that of the first rotary member.

5. A switch mechanism according to claim 4 in which the reduction gear through which the first rotary member drives the second rotary member consists of a number of intermeshing gear wheels rotating about the two parallel axes.

6. A switch mechanism according-to claim 4 in which there are provided two collars which are secured adjustably respectively to said first and second rotary members so that their angular positions can be adjustedand which carry respectively said first and second abutments.

7. A switch mechanism according to claim 6 in which the abutment on the first rotary member is a radial shoulder on the collar, while the abutment on the second rotary member is an axial pin engageable with the shoulder, the first and second rotary members having opposite directions of rotation.

8. A switch mechanism according to claim 3 in which the axis of rotation of the second second rotary member is at right angles to that of the first, the reduction gear being a worm and wheel drive.

9. A switch mechanism according to claim 1 in which there is further provided a cam, a pivoted arm and a further spring, wherein said pivoted housing, on swinging about its pivot axis operates said switch by acting through said cam which bears against said arm at a point on the arm lying between its ends, one end of the arm being held by said further spring against the pivot of the arm, while the other end of the arm is arranged to operate said switch when the arm is tilted about its pivot by said cam, the arrangement being such that the arm can as a safeguard move away from its pivot, against the action of said further spring in the event of the cam continuing its movement after the switch has been operated.

10. A switch mechanism according to claim 1 in which there are two pairs of abutments on the two rotary members which act to tilt the housing in opposite direction, depending upon the direction of rotation of the first rotary member, to operate either one of two oppositely disposed switches.

ll. A switch mechanism according to claim 1 including a torque-limiting device and a further switch wherein said switch is operated by said torque-limiting device when said actuator torque exceeds a predetermined value.

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