AU729109B2 - Improved actuator mechanism - Google Patents

Description

AUSTRALIA

Patents Act 1990 FF SEELEY NOMINEES PTY LTD

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Improved actuator mechanism The following statement is a full description of this invention including the best method of performing it known to us:- Throughout this description and the claims which follow, unless the context requires otherwise, the word "comprise', or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

This invention relates to a mechanism for actuating a device using an electric motor that has significant advantages over the prior art including less susceptibility to failure and the ability to be de-energised without loss of function. This type of actuation device has been found to be particularly useful in actuating drain and inlet devices in the field of evaporative air coolers. It should be recognised however that the use of this invention is not limited to this particular field.

15 Prior Art means in the field of operating the outlet and inlet valves, drain valve and float valve, of evaporative air coolers known to the applicant consists primarily of wax pellet actuators. An evaporative cooler comprises a reservoir of water which is maintained at a particular volume during operation of the evaporative cooler. As operation of the evaporative 20 cooler consumes water in effecting the cooling operation, water supply into the reservoir is required to maintain water level within the reservoir.

However, there is a requirement from time to time to be able to drain the contents of the reservoir of an evaporative cooler such as when the cooler is not intended to be used for an extended period of time. This requirement is 25 currently achieved by mechanisms which control the water supply to the reservoir and operate a drain valve at the base of the reservoir.

S"As previously mentioned, a common device used for this purpose, and in fact employed by the applicant prior to this invention, is the wax pellet actuator. This device is an active device and operates on the principle of thermal expansion of the wax upon the application of electrical power. The expansion of the wax is sufficient to provide physical actuation of the p appropriate inlet or outlet valves to perform the required function. This type of device is generally housed in a steel casing which contains the wax with a plunger passing through a teflon bushing into the housing and in communication with the wax. The steel housing is generally supplied with a heating means attached to the outer of the steel casing. Upon heating the steel casing, the wax is caused to expand which in turn urges the plunger outwardly from the steel casing. The teflon bush acts as a seal around the plunger enabling lateral movement of the plunger whilst containing the wax inside the steel casing. During normal operation of this type of device, it appears that relatively high pressures are generated internal to the steel casing in causing expansion of the wax. This in turn has been found to eventually cause the teflon bush to grip the plunger shaft thereby restricting the plungers lateral movement through the teflon bush. At this point the device ceases to operate reliably and requires replacement. The reliable life of this type of device is related to the amount of time that the device is to energised and as this type of device is required to be energised continuously to provide actuation, the reliable life of the device is diminished rapidly.

Ultimately, this translates to the device suffering from a relatively high failure rate. Whilst the failure rate of these devices is a major problem, the devices also exhibited other disadvantages such as limited available stroke 15 and limited thrust in performing an actuation.

An alternative means for providing the required physical actuation could be a solenoid. However, this approach suffers from requirement for the solenoid to be continuously energised for particular states of operation, a requirement which is infeasible when considering the possibility of power 20 failure to the evaporative cooler, and in addition, solenoids also suffer from a relatively high failure rate.

Another alternative is a water hydraulic actuator. However, these devices also require continuous energisation, and also suffer from a relatively high failure rate. In addition, these types of actuator suffer from long term creep resulting from the continuously stressed plastics involved which in turn leads to failure.

It is an object of this invention to provide an electrically controlled actuator which exhibits a lower failure rate as compared with prior art devices.

It is a further object of this invention to provide an electrically controlled actuator which incorporates the characteristics of a device which only requires electrical power during required state changes.

In its broadest form the invention comprises a mechanism for controlling entry or exit of water from a tank, said mechanism comprising a movable valve member biased to close an opening in the tank, symmetrical camming means driven by a bi-directional electric motor, said camming means being adapted to actuate at least one motor controlling switching means upon rotation of the camming means, means for moving the valve member to open the opening in a predetermined relation to the actuation of the at least one switching means and wherein rotation of the camming means effects activation or de-activation of said at least one switching means at positions where the valve member opens or closes said opening.

*oooo* o **e o *o One embodiment of the mechanism of the present invention is in an environment where the device is a plunger and the means for actuating the at least one switch mechanism comprises notches or projections on the periphery of the camming means, and said further means for actuating the device comprises further notches or projections to actuate the plunger into an extended or retracted state.

In another aspect the invention provides an electrical circuit, in combination with the aforesaid mechanism, said electrical circuit interconnecting the at least one switch mechanism, the electric motor and a control element such that a predetermined signal from the control element results in the supply of power to the electric motor and a resulting rotation of the camming means until the supply of power is interrupted by activation of a switch by the camming means, activation of said switch corresponding to a position of the camming means relating to one of the two differing states of the device such that said signal from said control element causes a change in the state of the device and wherein a subsequent predetermined signal from In a further embodiment an actuator mechanism of this invention is provided wherein the mechanism comprises a synchronous clock motor and gearbox arrangement and the camming means comprises two cams rigidly attached to the output shaft of the gearbox arrangement. The synchronous motor and gearbox arrangement is of the type used as a timing controller for apparatus such as a washing machine' electric clothes drier or an electric range. As a result of the large quantities of such timing controllers produced 25 worldwide and the relatively large quantity that have been produced to date, the failure rate and cost of such devices has been reduced to a relatively low level. The failure rate of these types of electrical timing devices is relatively low as compared with the failure rate of actuation devices previously known in the field of evaporative coolers.

One of the two aforementioned cams of the further embodiment bears against a plunger arrangement which performs the required actuation stroke.

The remaining cam operates two limit switches that are positioned such that a recess in the cam operates one of the switches when the plunger is fully retracted and the remaining switch when the plunger is fully extended. The positioning of the limit switches is such that the output shaft of the synchronous motor gearbox arrangement is only required to traverse one half of a full rotation to either fully extend or fully retract the plunger. The switch operating cam is symmetrical about a plane bisecting the recess and is coincident with the axis of rotation. This enables the correct operation of the limit switches irrespective of the direction of the rotation of the synchronous motor. The direction of rotation of the synchronous motor upon the application of power can depend upon the initial resting position of the permanently magnetised rotor. However, the positioning of the limit switches and the symmetrical arrangement of the switch operating cam allows the motor to operate in either direction of rotation to effect the actuator's operation.

The switch operating cam is substantially circular and operates to retain spring actuated limit switches bearing against the cam in their closed positions unless the switch is aligned with the recess of the cam. In this embodiment there is only a single recess in the periphery of the cam enabling the operation of only one spring loaded switch at a time. The spring loaded switches bearing against the cam, have electrical connections to the contacts corresponding to their normally open contacts. A switch not aligned with the cam recess has its spring actuated switch held in the closed position. As the cam turns, the recess of the cam is eventually aligned with the switch 20 and allows the switch to operate thereby opening the electrical circuit to which it is connected. The two limit switches which act to disconnect supply to the motor upon reaching either the fully extended or fully retracted position are physically disposed a half circle apart around the periphery of the cam.

25 During normal operation of a domestic evaporative cooler, single :phase power from the electrical supply authority is available. This particular actuation arrangement can be operated from a single phase supply and further employs a control line which itself is a supply of the power available to the unit. This approach has the advantage that there is no requirement to provide a conditioned control signal for the control of the actuator. In this embodiment, the control circuit comprises a relay which provides power to the synchronous motor in combination with and depending upon the state of the limit switches at any point in time.

The plunger activating cam is rigidly attached to the output shaft of the synchronous motor gearbox arrangement and is also rigidly attached to the switch operating cam. The plunger activating cam is symmetrical enabling the activation of a plunger when rotating in either direction. The main lobe of the plunger activation cam is disposed from the location of the recess of the switch operating cam by approximately a quarter circle, or degrees. Again, the positioning and shape of the plunger activating carnis such that the operation of the plunger from, its fully retracted position to its fully extended position, is not dependent upon the direction of rotation of the synchronous motor.

Under normal operating conditions, the switching cam will have its recess aligned with and have activated a limit switch thereby disconnecting power to the actuator. To effect actuation a relay is activated and provides power supply to the motor through the limit switch which is currently in a closed condition (ie the limit switch which is not aligned with the switching cam recess). The supply of electrical power to the actuator through the closed limit switch causes the synchronous motor to rotate. The direction of rotation of the motor is not important as a half a rotation of the output shaft in either direction will cause the recess of the switching cam to operate the limit switch that is enabling power supply to the motor. Upon the recess of the switching cam aligning itself with the limit switch, the switch is allowed to open thereby cutting supply of power to the motor. At the same time, the 20 plunger actuating cam will have caused the plunger to change state from fully retracted to fully extended, or vice versa Deactivation of the relay will .''"enable transition of the actuator from this state back to its former state by providing power once again to the motor through the closed limit switch.

Transition of the actuator from one state to the other only requires S: 25 power to be supplied to the synchronous motor during the transition phase.

At the completion of a state transition the power supply to the actuator is disconnected. The mechanical locking of the actuator at either position by way of the de-energised synchronous motor and gearbox arrangement enables this actuator to hold or retain its position with the power supply to the actuator removed. In addition, if power supply to the actuator is interrupted during a transition phase, for reasons of power failure to the unit for example, then upon supply of power being re-established the actuator will continue the transition that it had commenced prior to interruption.

In an alternative embodiment of the invention, the electrical control circuit comprises two silicon controlled rectifiers which are employed to provide the control and drive for the actuator.

In relation to the use of the actuator for the purposes of controlling the inlet and outlet valves for an evaporative cooler reservoir, two individual actuators are employed with one for control of the inlet valve and the other for control of the outlet valve. In yet another embodiment of the invention, the control circuit for the pair of actuators comprises interlocking logic to effect a complete transition of the actuator controlling the outlet valve prior to operating the actuator for the inlet valve. This particular arrangement enables the reservoir to be drained completely and the outlet valve closed prior to the opening of the inlet valve to refill the reservoir. This avoids the possibility of fresh incoming water escaping from the reservoir through the open outlet valve.

Although the invention need not necessarily include the abovementioned details an embodiment is described hereunder in some further detail with reference to and is illustrated in the accompanying drawings, in which: Fig 1 is an end view of an actuator detailing the switch operating cam and the plunger activating cam with the plunger fully retracted; Fig 2 is an end view of an actuator detailing the switch operating cam and the plunger activating cam with the plunger fully extended; 20 Fig 3 is a circuit diagram of a relay controlled activation for the actuator; ~Fig 4 is a circuit diagram of a silicon controlled rectifier activation for the actuator; and Fig 5 is an embodiment of the invention for the purpose of 25 controlling the inlet and outlet valves for the reservoir of an evaporative cooler.

Fig 1 details an end view of an actuator 5 and details the relative positioning of the synchronous motor housing 10, the limit switches 12 and 13, the plunger activating cam 15, the switch operating cam 17, the plunger 25 and actuating lever 27 and return spring 28. Also detailed in Fig 1 is the output shaft 30 of the synchronous motor gearbox arrangement and the electrical contact points 32 and 34 of the limit switches 12 and 13. In the position detailed in Fig 1, the switch operating cam 17, has its recess 18 aligned such the spring loaded limit switch plunger 20 of limit switch 12 is released. In this position, with the limit switch plunger 20 in its extended or released position, an open circuit condition exists between the electrical contacts 32. In this position also, the spring loaded limit switch 22 of limit switch 13 is retained in its retracted position resulting from its abutment with the switch operating cam 17. In the position detailed in Fig 1, a closed circuit condition exists between the electrical contacts 34 of limit switch 13.

Also, in the position detailed in Fig 1, the plunger operating cam 15 is in its fully retracted position with plunger 25 and actuating lever 27 held in its fully retracted position by return spring 28.

Upon supply of power to the synchronous motor gearbox arrangement 10, through the closed contacts of limit switch 13 the output shaft 30 will rotate. In the embodiment developed by the applicant the speed of rotation of the output shaft is approximately 4 rpm. As with all single phase synchronous motors, the direction of rotation upon application of power is difficult to predict and depends to a large extent upon the initial position of the permanently magnetised rotor. In this invention however, the direction of rotation of the motor is not important as the symmetry of the switch operating cam 17 and the shape and positioning of the plunger operating cam 15 ensure correct operation of the limit switches 12 and 13 irrespective of the direction of rotation. To effect a transition of the actuator 5, power is supplied through the closed contacts of one of the limit switches 20 12 or 13 whilst not supplying power to the open contacts of the remaining limit switch. In the situation detailed, supply of power through the closed '...contacts of limit switch 13 effects rotation of the output shaft 30 which in turn causes rotation of the switch operating cam 17 and the plunger operating cam 15. Rotation of the cams 15 and 17 will continue until the 25 recess 18 is aligned with the spring loaded plunger 22 of the limit switch 13.

*At this point, power will once again be disconnected to the actuator however, the plunger operating cam 15 will have rotated through a half circle, or approximately 180 degrees, and will have effected a transition in the state of the plunger 25 as detailed in Fig 2.

Fig 2 details the actuator 5 in its alternate state with the plunger and the actuating lever 27 in their fully extended position with the return spring 28 also fully extended. Effecting a change in state of the actuator back to the position illustrated in Fig 1, can be achieved by the supply of power to the synchronous motor through the closed contacts of limit switch 12' whilst not supplying power to the contacts of limit switch 13'.

Fig 3 details an electrical control circuit arrangement for the control of the actuator. The active of a 240 Volt single phase supply is designated A' with the neutral being designated The single phase power is applied to the motor 32 by various combinations of the switches 35, 36, 37 and 38.

Switch 35 represents normally closed contacts of a relay whilst switch 37 represents normally open contacts of the same relay. The relay control signal applied to an activating coil of the relay can also be the same as the main supply to the motor 32 thereby eliminating the requirement to perform any signal conditioning to the control signal. Switches 36 and 38 represent the electrical operation of the limit switches 12 and 13 of Fig 1, respectively, whilst motor 32 represents the synchronous motor of the actuator The condition detailed in Fig 3 with switch 35 closed and limit switch 36 open, would correspond to switch 37 being in the open condition and limit switch 38 being closed. A change in state of the actuator is effected via this circuit by effecting a change in state of the relay contacts of switches es: 35 and 37. By causing the relay contacts of switch 35 to become open and relay contacts of switch 37 to become closed, power will then be supplied to the motor 32 via limit switch 38. This will continue until limit switch 38 is opened by alignment of the switch operating cam recess with the limit 20 switch thereby opening the electrical contacts of switch 38. Again, to effect another change in the state of the actuator back to its previous condition, a change in state of the relay will cause the relay contacts of switch 37 to open .and relay contacts of switch 35 to be again closed. This will allow power to be supplied to the motor 32 via the closed contacts of limit switch 36.

25 Again, the motor 32 will operate until the contacts of limit switch 36 become open circuited.

Fig 4 details an alternative embodiment of the electrical control *circuit which replaces the relay of Fig 3 with silicon controlled rectifiers and 42. The main single phase power supply to the unit is designated A' whilst the neutral is designated A control signal to effect a state change of the actuator is designated 'Control'. Operation of the circuit in Fig 4 is based upon the same principles as that for Fig 3 with power supplied to the motor 32' through the closed contacts of one of the limit switches 36' or 38' except that the supply of power exclusively to one set of these contacts is performed by the operation of the silicon controlled rectifiers 40 and 42.

With the main supply A' supplying power to the rectifier 40 and the gate of the same rectifier 40 through resistor R1, rectifier 40 will only supply power to the limit switch 36' if rectifier 42 is not conducting (ie the control signal is absent). If this condition is satisfied then the motor 32' will operate until the limit switch 36' opens its contacts. Effecting a change of state in the actuator can be achieved by connection of the main supply to the 'Control' line which will cause rectifier 42 to conduct by supplying a sufficient gate signal through resistor R2. At the same time, the 'Control' signal provides power to the motor 32' through the closed contacts of limit switch 38'.

Simultaneously, rectifier 40 will not be in a conductive state as rectifier 42 conducting will cause a voltage drop across resistor R1 and insufficient gate voltage for rectifier 40 to conduct.

Fig 5 details an embodiment of the electrical control circuit for the purpose of controlling the inlet and outlet valves for the reservoir of an evaporative cooler wherein the outlet valve of the reservoir is allowed to be operated and fully closed before allowing fresh water into the reservoir through an inlet valve.

In Fig 5, switch 47 is connected directly to the single phase supply ::designated A' and is used to control the state of the evaporative cooler reservoir. The switch positions corresponding to the "fill" and "empty" state 20 of the reservoir are designated on switch 47. Switches 48 and 49 comprise the normally closed and normally open contacts of a limit switch of an inlet valve actuator. As shown in Fig 5, the switch positions correspond to a closed inlet valve to the reservoir. The remaining limit switch of the inlet valve actuator is detailed as switch 53. Switches 51 and 52 comprise the 25 normally open and normally closed contacts of a limit switch of an outlet valve actuator. As shown in Fig 5, the switch positions correspond to an open outlet valve (ie switch 47 in "empty" position). M1 represents the electric motor of the inlet valve actuator and M2 represents the electric motor of the outlet valve actuator.

Upon switching switch 47 to the "full" position, power is supplied to the outlet valve motor M2 and as a result, the motor M2 will cause the actuator to close the outlet valve. Upon closure of the outlet valve, switch 52 will be in the open position, switch 51 will be in the closed position and switch 50 will be closed. Upon closure of switch 51, in combination with switch 53, power is supplied to motor M1 which causes the inlet valve actuator to open the inlet valve. Actuation of the inlet valve continues until 11 switch 53 is opened. At the same time, switch 49 is closed and switch 48 is opened. This establishes the correct switch positions such that return of switch 47 to the "empty' position will cause the inlet valve to be closed prior to the outlet valve being opened to drain the contents of the reservoir.

With the above identified embodiments, the applicant has provided an actuator which incorporates a number of significant advantages. These advantages include an actuator for which the position of the plunger is only determined by the state of the control line, no energisation is required for the actuator in either of its resting states (ie fully extended or fully retracted), the actuator is mechanically locked in either plunger position and the plunger will continue a transition from one state to the other upon re-establishment of the power supply to the motor in the event that there is an interruption of the power supply to the motor during the transition.

These identified features provide a significant advantage as compared with the prior art especially as they are achieved with an actuator that displays a relatively lower failure rate as compared with prior art devices.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the 20 invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

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Claims (7)

1. A mechanism for controlling entry or exit of water from a tank, said mechanism comprising a movable valve member biased to close an opening in the tank, symmetrical camming means driven by a bi-directional electric motor, said camming means being adapted to actuate at least one motor controlling switching means upon rotation of the camming means, means for moving the valve member to open the opening in a predetermined relation to the actuation of the at least one switching means and wherein rotation of the camming means effects activation or de-activation of said at least one switching means at positions where the valve member opens or closes said opening.

2. A mechanism as claimed in claim 1, wherein the means for moving the valve member is a further camming means driven by the electric motor.

3. A mechanism as claimed in claim 1 or 2, wherein the symmetrical camming means and the means for moving the valve member are fixed to a common shaft rotatable by said motor.

4. A mechanism as claimed in any one of the preceding claims, wherein the movable valve member is a plunger arrangement. oeooo.

5. A mechanism as claimed in any one of the preceding claims comprising an electrical circuit interconnecting the at least one switching means, the electric motor and a control element such that a predetermined signal from the control element results in the supply of power to the electric motor and a resulting rotation of the symmetrical camming means until the supply of power is interrupted by activation of the at least one switching means by the symmetrical camming means, activation of said at least one switching means corresponding to a position of the symmetrical camming means relating to one of the opening or closing of the valve member and wherein a subsequent predetermined signal from said control element causes closing or opening, respectively, of the valve member.

6. A mechanism for controlling the entry or exit of water from a tank using an electric motor substantially as hereinbefore described with reference to Figs 1 and 2 of the accompanying drawings.

7. A mechanism as claimed in claim 6 further comprising an electrical control circuit substantially as hereinbefore described with reference to Figs 3, 4 or 5 of the accompanying drawings.