US3418499A - Bimetal motor step drive - Google Patents

Description

Dec. 24, 1968 J. J. LESTER 3,418,499 I BIMETAL MOTOR STEP DRIVE Filed Dec. 2'7, 1965 2 Sheets-Sheet 1 \uvENToR J HN J. LESTER A'r'roanev Dec, 24, 1 968 J. J. LESTER BIMETAL MOTOR STEP DRIVE 2 Sheets-Sheet Filed Dec. 27, 1965 Hui-P hwam'rog JO J. Las-raR ATTORNEY BY z /z/ United States Patent 3,418,499 BlME-TAL MOTOR STEP DRIVE John Joseph Lester, Brookfield, Wis., assignor, by mesne assignments, to Controls Company of America, Melrose Park, Ill., a corporation of Delaware Filed Dec. 27, 1965, Ser. No. 516,266 11 Claims. (Cl. 310-4) ABSTRACT OF THE DISCLOSURE A heat motor operated step drive is disclosed wherein a bimetal operated drive pawl and a latch pawl step a toothed wheel in response to energization of a heater associated with the bimetal. The drive pawl slides on the latch pawl during the drive step and the heater circuit is intermittently made through the drive and latch pawls as they are alternately engaged and disengaged, a contact button providing the medium of engagement between the latch and drive pawls. The latch pawl includes a guide for maintaining relative alignment of the latch pawl, drive pawl and toothed wheel, and the drive pawl has an articulated connection with the bimetal with the drive pawl being biased into engagement with the latch pawl and bimetal. In another aspect, the drive metal is supported by an ambient temperature compensating bimetal.

This invention relates to drive mechanisms and, more particularly, to step drives of the type used, for example, to control switch operation in timers or the like.

Various step drive arrangements have been proposed in the past and some have utilized a heat motor incorporating a bimetal-heater arrangement as the source of motive power. An example of a heat motor using a bimetal-heater arrangement is found in Patent No. 2,487,- 154 of Tom C. Lloyd and assigned, by mesne assignments, to the assignee of this application. This invention is specifically concerned with an improvement in heat motor drives of the type disclosed in the aforementioned patent. In that patent the bimetal drive rotates a ratchet wheel in response to energization of a bimetal heater and uses a combination of a drive pawl and latch pawl, the drive pawl steps the ratchet wheel and the latch pawl holds a previously taken step while the drive pawl is repositioned for a subsequent step. The latch and drive pawls complete the circuit to the bimetal heater and are separated to de-energize the bimetal heater at the completion of a particular step and are re-engaged to reenergize the heater for another step when the drive pawl has been returned to its initial driving position.

A general object of this invention is to provide an improved heat motor drive of this type.

Another object of this invention is to provide a mounting arrangement of the latch and drive pawls which insures a low resistance electrical connection therebetween; and, moreover, an arrangement which maintains this low resistance connection throughout relative driving movement between the drive and latch pawls and regardless of the temperature ambient the heat motor.

A further object of this invention is to provide an improved support arrangement for the drive pawl which insures proper alignment of the drive pawl with the driven member.

A still further object is to provide an improved connection between the drive pawl and bimetal element.

A further object of this invention is to provide an arrangement which achieves ambient temperature compensation in a heat motor of this type; and, more specifically, an arrangement which maintains a substantially uniform operational cycle regardless of the ambient temperature.

Other objects and advantages will be pointed out in,

or be apparent from, the specification and claims, as will obvious modifications of the embodiments shown in the drawings, in which:

FIG. 1 is a plan view of a switch mechanism and a heat motor driven actuator constructed in accordance with this invention;

FIGS. 2 and 3 tions of the drive ratchet wheels;

FIG. 4 is a section 44 of FIG. 1;

FIG. 5 is a plan view of an alternative embodiment illustrating the heat motor including ambient temperature compensation;

FIG. 6 is a plan view of a portion of the embodiment of FIG. 5 illustrating the relative position of the elements in an elevated ambient temperature condition; and

FIGS. 7 and 8 contain operational curves for a heat motor without and with ambient temperature compensation.

With particular reference to the drawings, a heat motor constructed in accordance with this invention is illustrated as including drive pawl 10, latch pawl 12, bimetal 14 and resistance heater 16. The drive and latch pawls cooperate to step ratchet wheel 18. Gear 20 rotates with ratchet wheel 18 and engages and drives gear 22 which in turn drives cam 24, the directions of rotation of the various members are illustrated by the arrows. Cam 24 is a part of a conventional timer switch arrangement 26 the construction and operation of which is well known and, therefore, a specific description will not be made in this application. For purposes of understanding this invention it is believed sufiicient to point out that switch blades 28, 30 and 32 are resilient and attached to terminals 34, 36 and 38 fixed to base 39. Rigid block 40 holds outer blades 28 and 32 out of engagement and maintains a minimum spacing therebetween. Movable switch blade 30 normally engages switch blade 28 and is engageable with switch blade 32 depending upon the position of cam 24, specifically cam lobe 24a, with respect to movable switch blade 30. Thus, the circuit established by timer switch 26 is determined by the rotation of cam 24 and the cams position with respect to switch blade 30.

The drive for cam 24 is determined by drive pawl 10 and bimetal 14. Structurally, bimetal 14 is supported from bracket 44 attached to base 39. Bimetal 14 extends from the bracket and is free to warp about its connection to bracket 44. The free end 46 of the bimetal extends into slot 48 in web 50 of the drive pawl and coil spring 52 is connected between post 54 attached to base 39 and tab 56 connected to web 50. Spring 52 extends angularly downwardly and back toward the bimetal to bias the drive pawl into engagement with the bimetal so that the drive pawl follows bimetal movement, and also biases the drive pawl into engagement with the latch pawl which provides support for the free end of the drive pawl, an advantageous operational arrangement as will be de scribed hereinafter.

Bimetal end 46 is reduced to provide shoulders 46a and 46b which engage the underside of web 50 at slot 48 and cooperate in establishing the connection between the bimetal and drive pawl. This connection limits longitudinal movement of the drive pawl on the bimetal in one direction while freely permitting it in an opposite direction. Limited clearance is provided between end 46 and the slot walls and this, together with the just-described restrained and free relative longitudinal movement in opposite directions provides an articulated joint which permits limited relative movement between the drive pawl and bimetal to insure proper alignment of the drive pawl with the bimetal illustrate successive operational posiand latch pawls with respect to the view taken generally along lines and also with the teeth of the ratchet wheel. Spring 52 biases the drive pawl in the proper direction (i.e. it takes up all lost motion in the connection between the bimetal and drive pawl) and, together with the latch pawl, permits the use of this articulated connection while insuring the necessary engagement between the drive pawl and bimetal to insure proper transmission of driving motion from the bimetal to the drive pawl.

The low expansion side of the bimetal faces toward ratchet wheel 18 so that when resistance heater 16 is energized the bimetal bows toward the ratchet wheel moving end 10a of the drive pawl into engagement with tooth 18a of the ratchet wheel. This movement of the drive pawl rotates the ratchet wheel counterclockwise.

Latch pawl 12 is resilient and is connected to base 58 fixed on base 39 so that the latch pawl is fixed and the ratchet wheel and drive pawl move with respect thereto. More specifically, as the drive pawl rotates ratchet wheel 18 counterclockwise the drive pawl slides along the latch pawl and tooth 18a moves away from and tooth 18b out from under the free end of the latch pawl. During this movement the end of the latch pawl bows upwardly (FIG. 2) and eventually latch pawl 12 is released from tooth 18b and snaps away from the drive pawl into engagement with the next tooth (FIG. 3) for latching engagement with tooth 18b to insure that the heat rnotor holds the step taken as a result of drive pawl movement.

At the end of the desired step, resistance heater 16 is de-energized allowing bimetal 14 to cool and causing the bimetal to move away from the ratchet wheel and return to its normal position. Spring 52 causes drive pawl 10 to follow the bimetal and the drive pawl moves away from tooth 18a. When the drive pawl clears tooth 1812, it is snapped back into engagement with latch pawl 12 and is positioned for driving engagement with tooth 18b whereupon the heat motor is ready for another step.

Preferably the electrical circuit for resistance heater 16 is established through the latch and drive pawls so that the circuit is maintained when the pawls are in contact during a drive step and it is automatically interrupted when the latch and drive pawls separate at the completion of a particular step. More specifically, latch pawl base 58 includes a terminal portion 60 to which an electrical lead (not shown) is connected and latch pawl 12 is made of electrically conductive material and is electrically and mechanically connected to terminal portion 60 by rivet 62. Preferably contact button 64 is engaged between the opposed surfaces 63 and 65 of the latch and drive pawls and is carried on the drive pawl. The contact button is spaced inwardly from the end of the drive pawl and when the bimetal is cold and it and the drive pawl are in the relaxed position the contact button engages the latch pawl at a point spaced from tooth 18b. With this arrangement, namely the latch pawl supporting the free end of the drive pawl, an adequate sliding surface is provided for the contact button and adequate contact pressure between the contact button and the latch pawl is maintained throughout the drive step. Spring 52 biasing the drive pawl toward the latch pawl maintains a low resistance connection between the contact button and the latch pawl. The contact button and is particular arrangement with respect to the latch and drive pawls also permits the latch pawl to bend around the contact button as the ratchet wheel rotates without pinching the latch pawl between the ratchet tooth and the drive pawl and without disturbing the driven movement of the drive pawl.

The electrical connection to the resistance heater is completed through the drive pawl, which is also made of electrically conductive material, lead wire 66 extending between the drive pawl and terminal 68 on the resistance heater, with the opposite terminal 19 of the resistance heater being connected to terminal 36 of the switch.

A further advantage in the illustrated embodiment resides in the specific construction of drive pawl 10 and base 58. Base 58 includes guide portion 72 of electrical insulating material and having a generally U-shapedconfiguration formed by base 74 and arms 76 and 78 extending from the base toward the drive pawl. The drive pawl fits into the open end of the guide and also includes arms 88 and 82 extending from web 58 generally parallel to arms 76 and 78 of the guide. Guide arms 76 and 78 are aligned with the ratchet wheel and this arrangement guides the drive pawl in its driven movement to insure engagement between it and the ratchet wheel. Clearance is provided between the arms of the guide and drive pawl to permit limited movement of the drive pawl with respect to the guide and the latch pawl to prevent stressing the elements but this clearance is limited so that movement is insufiicient to disengage either the drive pawl from tooth 18a or contact button 64 from the latch pawl. Also it will be noted that the drive pawl is spaced from base 74 of the guide when the elements are in their relaxed position and throughout driving movement to thereby insure maintaining adequate electrical engagement between the contact button and latch.

Starting with the bimetal in its normal, relaxed position (its cool position) as illustrated in FIG. 1, energization of resistance heater 16 through a suitable external source (not shown) will heat the bimetal and bow it toward ratchet wheel 18. Drive pawl 10 moves into engagement with ratchet tooth 18a with guide 58 guiding drive pawl movement and button 64 sliding along latch pawl 12 to maintain a low resistance connection in the energizing circuit of the resistance heater. The drive pawl engages tooth 18a and rotates the ratchet wheel with tooth 18b bowing the latch pawl toward the drive pawl. The arrangement of the button permits this bowing Without pinching and unduly stressing or disturbing the latch and drive pawls and insures an optimum electrical connection during relative movement between the drive and latch pawls. Spring 52 also cooperates with the button in maintaining the low resistance joint even though the latch pawl bows with respect to the drive pawl. Continued drive pawl movement and rotation of the ratchet wheel eventually moves tooth 18b from below the latch pawl and the latch pawl, by virtue of the internal biasing force created therein as it is bowed by tooth 18b, snaps away from the drive pawl. The latch pawl and button are separated interrupting the circuit to the electrical resistance heater at the same time that the latch pawl is positioned for engagement with tooth 18b to prevent the ratchet wheel backing up. At this point the free end of the drive pawl is supported on tooth 1811. Upon interruption of the circuit to the heater the bimetal cools and starts to return to its normal relaxed position drawing the drive pawl away from tooth 18a. Eventually the drive pawl will clear tooth 18b and spring 52 will snap the drive pawl into engagement with the latch pawl. The heater is re-energized and the bimetal bows to start another step of the heater motor in the above described manner.

The illustrated articulated joint between the bimetal and the drive pawl permits movement of'the drive pawl for proper'driving engagement with the ratchet wheel.

Throughout operation of the heat motor spring 52 biases the drive pawl in the proper sense with respect to the bimetal and the latch pawl thereby taking up all lost motion in the articulated joint and maintaining a low resistance connection between the button and the latch pawl. Both of these features insure proper start-up char acteristics regardless of the temperature ambient the heat motor, particularly with regard to the arrangement of spring 52 which insures a low resistance joint regardless of the ambient temperature and the position of the drive pawl and the bimetal as a result of that temperature.

In a heat motor drive of this type it is desirable to maintain the step cycle relatively uniform regardless of the ambient temperature in which the heat motor is working. That is, the period from initial energization of the heater to start a step through interruption of the heater circuit at the end of one step to re-establishment of the heater circuit to initiate a subsequent step should remain relatively uniform regardless of ambient temperature. The construction discussed to this point insures proper electrical connection regardless of bowing of bimetal 14 due to ambient temperature changes and it is proposed to achieve optimum ambient temperature compensation in the sense of maintaining uniform cycling time by adjusting the position of the drive pawl and bimetal with respect to the ratchet wheel in accordance with changes in ambient temperature.

With particular reference to FIGS. 5 and 6, this adjustment is achieved by connecting main drive bimetal 90 to compensating bimetal 92. Structurally the connection is made through thermal insulators 94 and 96 and rivet 98 also insulated from both bimetals 90 and 92. Bimetal 92 is fixed at one end to bracket 100 and bimetal 90 is connected and moves with the free end of the compensating bimetal as it bows about its fixed end due to changes in ambient temperature. The high expansion side of the compensating bimetal faces toward the ratchet wheel and bimetal 90 (downwardly in FIG. 5

When the ambient temperature increases bimetal 92 bows upwardly drawing bimetal 90 and drive pawl away from the ratchet (FIG. 6). This requires that heater 16' operate at a higher temperature to complete a drive step so that the heater and bimetal 90 work at a higher temperature when the ambient temperature increases. This maintains a relatively uniform temperature differential between the bimetal and the ambient and since it is this differential which determines the rate of bimetal cooling which in turn determines cycle time a relatively uniform cycle is maintained. This is illustrated graphically in FIGS. 7 and 8. Curve A illustrates a step cycle at generally expected ambient temperatures, e.g. 75 F. At point X the drive step is initiated, the bimetal temperature raises to point Y where the step is completed and the heater circuit is interrupted. The bimetal then cools to point Z whereupon the heater circuit is re-established for another step with T being the elapsed time. Curve B (FIG. 7) illustrates the same heat motor operating in an elevated ambient temperature, e.g. 125 F., and without ambient temperature compensation. The bimetal starts at point X (substantially the same as X) and the bimetal temperature rises to point Y where the step is completed and the bimetal starts to cool. Point Y is approximately at the same temperature as Y but cooling must occur in a higher ambient temperature where the differential between bimetal and ambient temperature is reduced and cooling occurs at a much slower rate to point Z and the elapsed time T is greater than T.

Curve C (FIG. 8) illustrates a heat motor operating in an elevated ambient temperature, eg 125 F., and with temperature compensation. In this instance the step is initiated at X a higher temperature than X or X and the bimetal temperature increases to Y a higher temperature than either Y or Y before the step is completed and the heater de-energized. The bimetal is then cooled but the temperature differential between Y and ambient is substantially the same as between Y and ambient so that cooling to Z occurs at substantially the same rate as from Y to Z and the elapsed time T from X to Z is approximately equal to T. In tests using the above mentioned ambient temperatures it was noted that Y and Y were approximately 400 F. and Y was approximately 450 F. thereby establishing the same temperature differential of 325 at both the expected ambient temperature of 75 and the elevated ambient It will be appreciated that the same adjustment takes place in a reduced ambient. When the ambient tempera ture falls below, for example, 75 F. bimetal 92 bows toward the ratchet wheel moving bimetal 90 and the drive pawl toward the ratchet wheel shortening the drive 6 stroke necessary to complete a step. This then reduces the temperature needed at bimetal to complete the step giving a lower operating temperature in a lower ambient to maintain a relatively uniform temperature differential.

In the selection of bimetals 90 and 92, bimetal 92 is made of more sensitive material to increase its responsiveness to ambient temperature variations. On the other hand, bimetal 90 is made of more rigid, less sensitive material so that it is virtually insensitive to changes in ambient temperature while still being responsive to the resistance heater, the variations in ambient temperature being relatively small in comparison to the change in temperature produced in bimetal 90 by the heater. In sulators 94 and 96 serve to thermally isolate bimetal 92 from bimetal 90 so that the compensating bimetal is not affected by the temperature of bimetal 90 as it is heated. Thus, bimetals 90 and 92 each respond to their own temperature condition without the temperature condition to which one is intended to respond adversely affecting the operation of the other.

The embodiment of FIG. 5 also illustrates an alternative arrangement for mounting the spring which maintains engagement of drive pawl 10' with the latch pawl 12' and bimetal 90. Here spring 52' extends between tab 56 on the drive pawl and a seat directly on bimetal 90. This arrangement maintains the proper engagement between the drive pawl and bimetal so that the drive pawl follows bimetal movement but isolates the spring forces from bimetal movement so that the bimetal, or bimetals, are free to bow without regard to the spring. This spring arrangement could also be used in the embodiment of FIGS. 1-4.

Another change in the heat motor is that heater terminal 69' is connected to terminal 36' by a flexible lead 91 to permit more freedom of movement for bimetal 90. Otherwise the heat motor and switch are the same as illustrated in FIGS. 1-4. It will also be noted that the illustrated arrangement of drive and latch pawls lends itself particularly well to provision of ambient temperature compensation. More particularly, the drive pawl being supported on the latch pawl and being freely movable with respect to the latch pawl without affecting the electrical connection between the drive and latch pawls permits the drive pawl to be moved to correct for ambient temperature variations without affecting either electrical or mechanical operation.

It will also be noted that the spacing between drive pawl 10' and web 74 of the latch pawl base 58 permits free movement of the drive pawl in response to movement of bimetal 92.

Although this invention has been illustrated and described in connection with particular embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

I claim:

1. A heat motor for driving a member having a toothed periphery and comprising, in combination,

bimetal means,

electrically energized heater means positioned operatively adjacent said bimetal means,

means supporting said bimetal means for movement in response to energization and de-energization of said heater means,

a drive pawl connected to and movable with said bimetal means and extending toward said toothed periphery for selective engagement with the teeth thereof,

a latch pawl adjacent said drive pawl and held against movement toward said member with said drive pawl, said latch pawl including at least a portion thereof extending coextensively with a portion of said drive pawl adjacent said toothed periphery and engaging the teeth of said periphery,

contact means connected to the projecting from one of said drive and latch pawls and having limited engagement with the other of said drive and latch pawls, said contact means engaged between said drive and latch pawls holding said drive and latch pawls in spaced relationship and providing a sliding electrical connection between said drive and latch pawls and a point about which said latch pawl bows as a result of driven movement of said member.

means biasing said drive pawl toward said latch pawl,

and means completing the electrical circuit for said heater means through said latch and drive pawls.

2. The heat motor of claim 1 wherein said support means for said bimetal means includes compensating bimetal means connected to said bimetal means and also including means supporting said compensating bimetal means for movement relative to said member in response to changes in the temperature ambient said heat motor with said compensating bimetal means arranged to move said bimetal means, in response to an increase in ambient temperature, in one direction to increase the movement of said drive bimetal means necessary to complete a step of said member and, in response to a decrease in said ambient temperature, in an opposite direction to decrease the movement of said drive bimetal means to complete a step of said member.

3. A heat motor for driving a member having a toothed periphery and comprising, in combination,

bimetal means,

electrically energized heater means positioned operatively adjacent said bimetal means,

means supporting said bimetal means for movement in response to energization and de-energization of said heater means,

a drive pawl connected to and movable with said bimetal means and extending toward said toothed periphery for selective engagement with the teeth thereof,

a latch pawl adjacent said drive pawl and held against movement toward said member with said drive pawl, said latch pawl including at least a portion thereof extending coextensively with a portion of said drive pawl adjacent said toothed periphery and engaging the teeth of said periphery,

contact means engaged between said drive and latch pawls holding said drive and latch pawls in spaced relationship, said contact means providing -a sliding electrical connection between said drive and latch pawls and a point about which said latch pawl bows as a result of driven movement of said member,

means biasing said drive pawl toward said latch pawl,

means completing the electrical circuit for said heater means through said latch and drive pawls,

said drive pawl being an elongated member and said latch pawl being an elongated member extending toward said periphery from a fixed mount disposed intermediate the ends of said drive pawl,

said drive and latch pawl having opposed faces between which said sliding electrical connection is made,

and said drive pawl moving longitudinally with respect to said latch pawl with said bimetal means.

4. The heat motor of claim 3 wherein said latch pawl extends from -a fixed mount spaced from said toothed periphery and including means defining a guide extending toward said drive pawl,

said drive pawl disposed within said guide,

and said guide defining a path for said drive pawl in the direction of movement thereof with respect to said periphery, said guide having limited clearance with said drive pawl to permit a limited amount of relative movement between said drive pawl and said guide suflicient to maintain said drive pawl substantially aligned with said toothed periphery and said latch pawl.

5. The heat motor of claim 3 wherein said contact means comprises a contact button engaged between said latch and drive pawls and holding said latch and drive pawls in relative spaced relation.

6. The heat motor of claim 3 wherein said member includes a toothed periphery defining successive latch and drive portions and wherein said drive pawl comprises a substantially rigid member extending from said point of connection toward said periphery with the distance between said point of connection and said periphery determining the amount of movement and correspondingly the temperature of said drive bimetal means necessary to move said member through an increment of movement, and including compensating bimetal means connected to said drive bimetal means and positioning said drive bimetal means with respect to said periphery,

and means supporting said compensating bimetal means for movement relative to said member in response to changes in the temperature ambient said heat motor to determine the position of said point of connection with respect to said periphery, said support means supporting said bimetal means to move said drive bimetal means and said point of connection away from said member in response to an increase in ambient temperature and toward said member in response to a decrease in ambient temperature.

7. The heat motor of claim 6 wherein said compensating bimetal means extends from the support means therefor and said drive bimetal means is connected to said compensating bimetal means at a point spaced from said support means,

and including means at the point of connection between said drive and compensating bimetal means for thermally isolating one from the other.

8. A heat motor for driving a member including means therein defining successive latch and drive portions spaced in stepped increments and comprising, in combination,

drive bimetal means, electrically energized heater means arranged in heat transfer relation with said drive bimetal means, means supporting said drive bimetal means for movement relative to said member in response to energization and de-energization of said heater means, a drive pawl disposed operatively adjacent said mem- Iber,

a latch pawl disposed operatively adjacent said mem ber and a portion of said latch pawl disposed adjacent a portion of said drive pawl,

connection means defining a connection between said drive pawl and drive bimetal means which prevents movement of said drive pawl in one direction with respect to said drive bimetal means and permits movement of said drive pawl in another direction with respect to said drive bimetal means,

means biasing said drive pawl in said one direction with respect to said drive bimetal means so that said drive pawl is movable with and follows said bimetal means and also biasing said drive pawl into engagement with said latch pawl so that said drive pawl is also supported by said latch pawl,

means providing a sliding electrical connection between said drive and latch pawls,

and means completing an electrical circuit for said heater means through said latch and drive pawls, energization of said drive bimetal means being maintained through said sliding connection as said drive pawl moves in response to bimetal means movement to drive said member, said sliding connection being interrupted when said member has been moved a suflicient distance to engage said latch pawl in a successive latch position and being re-established when said drive pawl is returned by said drive bimetal means to a successive drive position.

9. The heat motor of claim 8 wherein said member includes a toothed periphery and said successive latch and drive portions are defined by the teeth of said periphery,

said latch pawl extends from a fixed mount spaced from said toothed periphery and including means defining a guide extending toward said drive pawl,

said drive pawl disposed within said guide,

and said guide defining a path for said drive pawl in the direction of movement thereof with respect to said periphery and aligned with said toothed periphery, said guide having limited clearance with said drive pawl to permit a limited amount of relative movement between said drive pawl and said guide sufiicient to maintain said drive pawl substantially aligned with said toothed periphery and said latch pawl.

10. The heat motor of claim 8, wherein said connection means comprises a slot in one and a complementary shouldered projection in the other of said drive pawl and drive bimetal means,

said projection disposed in said slot and said biasing means biasing the shoulders of said projection and the walls of said slot into engagement.

11. The heat motor of claim 8 wherein said support means for said bimetal means includes compensating bimetal means connected to said bimetal means and also including References Cited UNITED STATES PATENTS 952,778 3/1910 Wohl et a1. 3104 2,326,002 8/ 1-943 Baak 3104 X 2,355,041 8/1944 Baak 310-4 2,487,154 11/1949 Lloyd 3104 2,707,737 5/ 1955 Rich et al 3104 X FOREIGN PATENTS 800,047 8/ 1950 Germany.

I. D. MILLER, Primary Examiner. D. F. DUGGAN, Assistant Examiner US. Cl. X.R. 58-23

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