US2641942A

US2641942A - Force applying tool

Info

Publication number: US2641942A
Application number: US745845A
Authority: US
Inventors: Mueller Otto
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-05-03
Filing date: 1947-05-03
Publication date: 1953-06-16
Anticipated expiration: 1970-06-16

Description

June 16, 1953 o. MUELLER 2,641,942

FORCE APPLYING TOOL Filed May :5, 1947 s Sheets-Sheet 1 INVENTOR- Offo Mueller.

TOR/VE/S.

June 16, 1953 0. MUELLER FORCE APPLYING TOOL 3 Sheets-Sheet 2 Filed May 3, 1947 W MW? 9 M \NI W VVVVVVYfiflV/A M R. w 7 my e w. v x M a 7 O k 7 1 p A 9 67 M VA a I r M a 7 3. I. a v 4 W H K BY v M- June 16, 1953 o, MU L 2,641,942

FORCE APPLYING TOOL Filed May 3, 1947 5 Sheets-Sheet 3 INVENTOR. Offo MUCIZC7X I Patented June 16, 1953 UNITED smrss earnest .orFIcE FORCE APPLYING .TOOL

Otto-Mueller, Dear-born, Mich.

Application May 3, 1947, Serial No. 7455845 This invention relates to pressureapplying de vices of 'a fluid actuated jaw type-for applying pressure for-performingriveting, welding, punching and like operations, and is a continuationin-part of applicants Patent No. 2,487,262, issued November 8, 1947. r

Ithas been the practice heretofore inthe art to utilize fluid pressure means for performing riveting and welding operations. Such devices usually apply the force directly from the piston to the work which requires the cylinder to be mounted abovethe work which at times limited the application of the device because of interfer ence. When the piston and cylinder were offset from the work, the mechanical efiiciency was usually lower, which oftentimesxresulted in defective work being performed.

The present invention embodies a pair of cradle jaws operated byta piston and cylinder remote from the ends which perform the operation upon the work. When the jaws are the same distance from their center of operation as the piston, the same*mechanicaladvantage is obtained. This may be increased or decreased by changing the relative position of the piston and cylinder and the work-engaging portion of the jaws relative to the jaw centers. v

The main objects of the invention are: to provide a compact pressure applying device having the operating arm located remotely from the force applying element; to provide a pressure applying device having a pair of rockable jaws mounted within an improved type yoke and operated by a cylinder and piston mounted at one end of the jaws for producing working pressure atthe opposite end-thereof; to provide a pair of 'rockable jaws having workperforming' arms at one end and arms on the opposite end to which a piston and cylinder are connected for applying a pressure thereto; to provide a novel connection between the arms and the piston and cylinder of the force applying element; to mount a pair of rockable jaws in a yoke in such a manner as to control the movement of the jaws when the pressure is applied thereto so that each moves a like amount relative to and from. each other; to provide means for limiting the opening movement of one of' said arms while permitting the other of said arms to be moved by the force applying means the full distance permitted therer by; to provide a'compact pressure applying device which may be mounted upon a fixture or which may be supported on a cable to be manipulated by the operator when performing-welding, riveting, punching or similar operations upon WOIk-r 6 Claims. (Cl. 78 -52) pieces; to provide an improved mounting means forsaid yoke including means therein to. limit the movement of one of said arms of said device; to provide a pressure plate between the movable jaws of the device which urges the workpieces together when being operated upon; to provide a device of the aforementioned type having an additional force applying means mounted in the working end of one of said laws for applying additional pressure to the work applying element mounted in said jaw; and, in general, to provide a force applying device which is simple in construction, positive in operation and economical of manufacture.

Other objects and features of novelty of the invention will be specifically pointed out .or will become apparent when referring, for a better understanding of the invention, to the following description taken in conjunction with the accompanying drawings wherein:

Figure '1 is a sectional view of a force applying tool embodying features of this invention;

Fig. 2 is a sectional view of the structure illustrated in Fig. 1, taken on the line 22 thereof;

Fig. 3 is a reduced, partially broken-away plan view of the structure illustrated in Figs. 1 and 2;

Fig. 4 is a broken front elevational view of a further embodiment of this invention, with parts shown in section;

Fig. 5 is a broken sectional view,'taken along the line 5-5 of Fig. 4;

Fig. 6 is a broken sectional View of a further embodiment of this invention;

Fig. 7 is a reduced view, partially in elevation and partially in section, of a further embodiment of the structure illustrated in Fig. 6;

Fig. 8 is a diagrammatic view of the hydraulic circuit for the device illustrated in Figs.'6 an'd'l;

and

Fig. 9 is a side elevational view illustrating a further embodiment of the invention.

Referring to Figs. 1 to 3, a force applying device is illustrated in the form of a riveting gun which embodies a supporting-yoke H which is herein illustrated as comprising a pair of interconnected parallel plates i 3 and Hi. The upper end of each of the plates l3 and B5 is formed with an inwardly extending annular flange l1. Disposed inwardly of the flanges I 'i, and supported on the inner peripheral surfaces thereof, are cylindrical sleeves 2! made of bearing material. Suitable lubricating passages 22 are provided in the flanges I! to lubricate the engaging bearing surfaces. Disposed on the center line of theflanges IIyand extending between the plates l3 and I5, is a spool element 23 having an annular flange or shoulder 24 formed on each end thereof. The spool element 23 is secured to each of the parallel plates I3 and I by means of screws 25 which are threadably received in tapped, central apertures 21 extending inwardly from each end of the spool 23.

Rockably supported within the yoke II is a pair of jaws 29 and 3|, each of which is formed intermediate the ends thereof with outwardly extending arcuate bosses 33 at each of its sides. When the jaws are positioned within the yoke II, the outer periphery of each of the bosses 33 is in sliding engagement with substantially one half of the inner periphery of the bearing sleeves 2|, and the inner periphery of each of the bosses 33 mates with the outer periphery of the spool 23 so as to be rockably supported thereon. The inner periphery of each of the jaws between the bosses 33 is provided with an inwardly extending arcuate portion 35 which is received between the shoulders or flanges 24 on the spool 23 to properly center the jaws with relation to the spool. The lower jaw 3| is shown as secured to the spool 23 by means of a key 31, for a reason which will be brought out below. In this way, it will be seen that the jaws 29 and 3| are rockably supported within the yoke II intermediate their ends.

The main pressure exerted by the jaws reacts through the area of engagement of the arcuate surfaces of each of the bosses and the bearing sleeve 2|. This area of engagement is substantial and the bearing material prevents the scoring of the metal of the engaging surfaces and produces a work applying force to the arms 39 and 4| of the jaws 29 and 3|, respectively, when a piston 43 and cylinder 45 are in an extended position.

The remote end of the piston 43 is connected to an arm 41 of the jaw 29 by means of a T- headed bolt 49. The opposite end of the cylinder 45 is similarly connected to an arm 5| of the jaw 3| by means of a T-headed bolt 53 which is identical with the T-headed bolt 49. the bolts 49 and 53 have a threaded stem portion 55 and a cylindrical head portion 51 which extends transversely of the stem portion 55. Each of the cylindrical head portions 51 is provided with a central longitudinal aperture 59 which communicates, in the center of the head, with a lubricating passage 6| for lubricating the cylindrical surface of the head 51 and its engaging arm surface. The cylindrical head portion 51 of each of bolts 49 and 53 is received in a more than semioylindrical aperture 53 in its respective arm 41 or 5|. The cylindrical bolt heads 51 extend outwardly on the opposite sides of their respective arm and the projecting portions are reduced in diameter as at 65. In order to retain the bolt heads against lateral movement within their arms, a washer 61 is inserted over each of the projecting ends 65 and seated against the respective arm side face, and a snap ring 69 is snapped over the ends 65 into an annular groove II in each of the projecting ends which prevents axial movement of each bolt head. The threaded stem 55 of the bolt 49 is threadably received in a tapped recess I3 in the remote end of the piston 43 and the threaded stem 55 of the bolt 53 passes through an aperture "I5 in the bottom wall of the cylinder 45 and a nut 11 is threaded on the end of the stem 53 and seats against the upper surface of the bottom wall of the cylinder to secure the bolt Each of I 4 thereto. The bottom of the piston head 19 is recessed as at to receive the nut 'I'I therein when the piston is in its bottom-most position.

The head I9 of the piston 43 is provided with grooves BI in which elastic rings 83 are mounted for providing a seal between the inner wall of the cylinder and the exterior surface of the head l9. Similar elastic rings 85 are provided in the cylinder head 81 for sealing therod portion of the piston 43 in the cylinder 45 for preventing the fluid in the cylinder from leaking. Fluid delivering conductors 39 and 9| are attached to opposite ends of the cylinder 45, communicating with passageways therein through which fluid is conducted to both sides of the piston head 19 for producing its movement within the cylinder 45. When fluid is delivered from the conductor 89 to the cylinder, the arms 39 and 4| of the device are moved to a separated position. When the fluid is reversed and delivered from the conductor 9| to the cylinder and expelled thereby through the conductor 89, the jaws are moved toward each other to perform a desired operation. I

In the structure illustrated in Figs. 1 to 3, an aperture 93 is provided near the end of each of the arms 39 and 4| for receiving the shanks 95 of riveting dies 91 which are mounted in an aligned relation. Suitable means, herein illustrated as setscrews 99, secure the riveting dies in position within the apertures 93.

Midway between the arms 39 and 4|, a resilient pressure plate Illl is provided which has an aperture I03 adjacent the outer end thereof through which the riveting die 91 of the arm 4| extends. The opposite end of the plate IIH is notched on opposite sides thereof, as at I04, and is inserted into a slot I05 in the spool 23. The screws 25 are received in each of the notches I94 on the opposite sides of the plate IUI to fixedly secure the latter to the spool 23. Due to the shape of the plate IIII, and the fact that the spool 23 is keyed to the movable jaw 3|, the forward end of the plate IOI will engage the under side of the workpiece I01 prior to the engagement of a rivet I99 by the riveting die 91 of the arm 4|. The further movement of the arms 39 and 4| toward each other produces the swaging of the end of the rivet against the workpieces I01 and the head of the rivet I09.

Disposed on the opposite side of the spool 23 from the plate IOI, and supported in the opposite parallel yoke plates I3 and I5, is a pin member III] which is supported in the plates I3 and I 5. The center portion I II of the pin member I I0 is of a larger diameter than the end portions, and the center portion III is eccentric with respect to the supporting end portions of the pin. The pin end portions are threaded as at H2, and nuts |I4 releasably lock the pin II!) to the plate members I3 and I5. However, by loosening the nuts II4, the eccentric center portion I of the pin IIO can be adjusted to face either of the jaws 29 or 3| to contact one sooner than the other so as to maintain the jaws substantially normal to the vertical axis of the yoke when in the open or closed positions.

When the jaws are applied to the rivet I99, the movement to closed position will first cause the die 9'! on the arm 39 and the spring pressure plate It! attached to the arm 4| to move into engagement with the head of the rivet I39 and the workpieces Iii'l, respectively, to force the head and sheets into intimate engagement with each other a the die 97 on the arm 4| continues to move to perform the swa'ging operation. Whenthe jaw positivelyretain the jaws in position relative to the yoke.

This pressure applying device may be mounted for operation in any suitable manner, such as by suspended cables (not shown) 'connected'to the yoke, so that it' may be-manually manipulated by an operator, or bysuitable stationary mounting means connected to the lower end of the yoke. As illustrated in Figs. 4 and 5, the yoke I I is shown as mounted ona stationary base II'3 by means ofa mounting member, generallyindicated at H5. The mounting'member H5 is positioned-between the lower ends of the parallel yoke plates I3 and I5 and secured to each of the plates by means of screws II'I received in vertically spaced apertures H9 ineach of the plates. The lower end of the mounting member H5 is bifurcated, as at I2I, to receive the'tongue portion of the base member H3. The mounting member H5 is secured to the base member H3 by means of a bolt I23, the head I25 ofwhich is shown as having the opposite sides thereof cut flat so as to be 'nonrotatably received in a slotted recess or groove I2I'in the mounting member I I5.

The mounting member H5 is provided between the vertically spaced bolts III with a tapped recess I28 into which a boltlike element I29 is threadably received. The inner end of the bolt element I29 is recessed as at I3I toslidably receive a flanged plunger I33 therein, the rear end of which projects through anaperture I34 in the mounting member H5 .and is adapted to contact the lower end of the'arm 5I of the law 3 I. The plunger I33 is actuated by'a spring I35 received within the bolt I29 and constantly urging the plunger I33 outwardly in the mounting member H5.

When the jaws and yoke are mounted in the mounting member H5, the eccentric pin III! is not used as the plunger I33 replaces it and limits the closing movement of the jaw 3 I. When the lower end of the latter contacts the spring plunger, the upper jaw 29 will continue to close, while the lower jaw III is limited or slowed down in its movement due to the plunger I33 .so asto maintain the proper angular relationship between the jaws 29 and 3I,'and the yoke II.

In the embodiment illustrated in..Fig. 6, a device similar to that illustrated in Figs. .1 to 3is provided which is adapted to 'performpunching operations or the like. In this deviceyjaws I3! and I39 are provided which are generally similar to the jaws 29 and SI previously described. The

jaws I31 and I39 are rockably supportedin a yoke I4! which likewise is generally'similar to the yoke I I previously described. However, it will be noted that the parallel plates of the yoke I4I are circular in shape and are not provided -with a depending portion adapted to be received in a stationary base. However, the yoke I M is adapted to be connected to cables or the like so as to be flexibly and movably supported, and a hand grip portion (not shown) may be provided -fcr manipulation of the device by an operator. 1 This device is provided with aneccentric pin I43 attached to opposite ends of the cylinder I45,

' communicating with passageways therein, through which fluid is conducted to both sides of the piston head for producing its movement within the cylinder. A punching die I5I is received in an aperture I53 intheopposite end of the jaw I31 and secured in the aperture by means of a setscrew I55. The 'working'end of the jaw I39 has a recess I51 therein which,'when an end plate I59 is sealingly'seoured in the lower end thereof by means of screws IIiI and an elastic ring I62, provides'a cylinderin-whioh'a piston I63 is received. 'Suitableelastic rings I55 are provided in the piston head for preventing the fluid in the cylinder from leaking. The rod portion of the piston I63 extendsupwardly through an aperture I56 in the jaw I39, and an'elastic ring I61 is provided in the wall of the aperture for sealing the rod portion of the plate. The remote end of the piston I63 has a punch I68 therein adapted to cooperate with the punching die I5! to punch holes in workpieces I69. In order to prevent the piston and punch from rotating,.a pin Ilil is provided which is pressed into a recess I'IIla in the cylinder head and slidably received in an aperture I'Iflb inthe piston head.

In order to supply fluid to actuate the piston I63, the jaw I39 is bored to provide a fluid passageway Ill communicating with the upper end of the cylinder I51, and a passageway I13 communicatingv with the lower end of the cylinder I57. Intermediate the ends of the passageway III and extending outwardly therefrom, is another bored passageway H! which, as can be seen in Fig. 8, is connected by suitable conduit means I13 through a four-way valve I8I and a pressure pump I82 to a fluid supply tank I 83. Below the passages III and I'll is a third passageway I84 which is connected by suitable conduit means I35 to the conductor M! which is attached to the upper end of the cylinder I45. Mounted in the jaw I39, and communicating with the-passageways III and III, is a pressure operated spring return type valve I81, the op eration of which will be hereinafter described.

Intermediate the ends of the fluid passageway H3, the jaw. I39 is bored to provide fluid passageways I89 and I90 which extend outwardly on oppositesides of the passage I 13. The passage I89 :is connected bya conduit I9! to the four-way valve ISI and thence to the fluid storage tank I83. The passageway I90 is connected by a conduit I93 to'the fluid delivery conductor I 49 attached to the lower end of the cylinder I35. Disposed in the rear end of the passageway I "I3, and

communicating with the passageways I89 and 196, is a pressure "operated spring return type the punch and punching die are separated from each other and it is desired to close them, the

fluid is pumped under pressure from the fluid pump I82 through the four-way valve I8I and to the mounting means 255.

through the conduit I9I. As the fluid passes through the valve I86, it is not under suflicient pressure to open the valve, and thus the fluid flows through the passage iSB and the conduit I93 into the bottom portion of the cylinder I45 to cause the working end of the jaws to close. When the piston I46 has moved upwardly to a point where the punching die II and the punch I68 are in contact with the work-piece 569, the pressure will build up within the cylinder I45. When this occurs, sufflcient pressure will be created to open the valve I98 and force the fluid under a high pressure through the passageway I13 into the lower end of the cylinder I51, thus forcing the piston I83 upwardly so as to push the punch I57 through the workpiece and on into the punching die I5I. When the pistons I46 and I63 are forced upwardly in the aforedescribed manner, the fluid in the upper end of the cylinder I45 flows through the conductor I47, the conduit I85, the valve I3? and back to the storage tank, while the fluid in the upper end of the cylinder I5! flows through the passage Ili, the valve I8? and back to the storage tank.

When it is desired to open the working ends of the jaws and separate the punch I6! from the punching die Ifll, it is necessary to remove the punch from the die before the jaws are opened. Therefore, the four-way valve It! is actuated to connect the conduit H9 with the pump I32 to pump the fluid into the passageway Ill in thejaw I39. The fluid can then through the passageway III to the upper end of the cylinder I51, but cannot pass back into the cylinder I 55 due to the fact that the valve I8? is closed and there is not suiiicient pressure to open the same. When the piston I53 has moved completely down so as to withdraw the punch I59, pressure will build up in the upper end of the cylinder I57. This pressure will cause the valve i8! to open and thus allow the flow of fluid through the passageway I34 into the conduit I85 and into the fluid delivery conductor It? in the upper end of the cylinder I45. When this occurs, the piston I46 will be forced downwardly, thus causing the working end of the jaws I3? and I39 to open, thus completing the cycle. The fluid in the lower end of each of the cylinders, when the pistons are forced downwardly, will flow through its respective conduits and valve I96 back to the supply tank I83.

In the embodiment illustrated in Fig. '7, the punching type force applying tool construction illustrated in Fig. 6 is shown as mounted in a yoke I95 formed of parallel side plates generally in the same manner as in the previous embodiments. It will be noted that the side plates of the yoke I 95 have downwardly depending leg portions which are cut back on the rear face to provide clearance for the fluid conduits and which are bifurcated as at I97 at their lower ends to receive a tongue I99 of a stationary mounting base. The yoke is secured to the mounting base tongue by means of a bolt and nut 2M.

Fig. 9 illustrates a further embodimentof the invention which is similar to the construction illustrated in Figs. 1 to 3. However, in this embodiment the yoke 203, instead of depending vertically with respect to the jaws of the device, extends horizontally and rearwardly from the mounting point of the jaws. Suitable mounting means 205 are provided for mounting the rear end of the yoke 263 to a stationary base, and bolts 20! are provided for securing the yoke It will be noted that the upper jaw 209 of this embodiment is shaped differently from the lower jaw 2| I and has a vertical center portion 2I3 intermediate the ends thereof which positions the rear arm portion 2I5 of the jaw 209 well above the lower jaw ZII. The lower jaw! extends substantially horizontally to the rear and the piston and cylinder actuating means 2i! is then secured to the ends of the jaws 2G9 and 2H in a manner similar to that described for Figs. 1 to 3. Riveting dies 2I9 likewise may be provided on the working end of the jaws in a manner similar to that previously described.

What is claimed is:

1. In a force applying tool, a pair of parallel plates each having an inwardly extending annular flange in spaced aligned relation, bearing means releasably secured between said plates on the center line of said flanges, a pair of rockable arms disposed between said plates and each having outwardly extending bosses formed thereon intermediate the ends thereof, sleeve means on said plates engaging the inner surfaces of said annular flanges, the inner periphery of each of said arm bosses mating with the bearing surfaces of said bearing means, the outer periphery of each of said arm bosses mating with a portion of the inner periphery of said sleeve means, means for supporting said plates, force applying means disposed between the ends of said arms on one side of the supporting plates for moving the ends away from each other when moving the opposite ends of the arms toward each other with a predetermined pressure, and work applying elements disposed on the ends of the arms opposite to that actuated by the force applying means.

2. In a force applying tool, a pair of parallel plates each having an inwardly extending annular flange in spaced aligned relation, the inner peripheries of said flanges lying on a common center, spool means disposed between said plates on the center line of said flanges, means securing each or" said plates to said spool means, a pair of rockable arms disposed between said plates and each having outwardly extending arcuate bosses formed thereon intermediate the ends thereof, sleeve means on said plates engaging the inner surfaces of said annular flanges, the inner periphery of said arm bosses being rockably supported on said spool means and the outer periphery of said arcuate arm bosses being in sliding engagement with the inner periphery of said sleeve means, force applying means disposed between the ends of said arms on one side of the supporting plates therefor for moving the ends away from each other when moving the opposite ends of the arms toward each other with a predetermined pressure, and work applying elements disposed on the ends of the arm opposite to that actuated by the force applying means.

3. In a force applying tool, -a pair of parallel plates each having an inwardly extending annular flange in spaced aligned relation, the inner peripheries of said flanges lying on a common center, spool means disposed between said plates on the center line of said flanges, means securing each of said plates to said spool means, a pair of rockable arms disposed between said plates and each having outwardly extending arcuate bosses formed thereon intermediate the ends thereof, sleeve means on said plates engaging the inner surfaces of said annular flanges, the inner periphery of said arm bosses being rockably supported on said spool means and the outer periphery of said arcuate arm bosses being in sliding engagement with the inner periphery of said sleeve means, force applying means disposed between the ends of said arms on one side of the supporting plates therefor for moving the ends away from each other when moving the opposite ends of the arms toward each other'with a predetermined pressure, work applying elements disposed on the ends of the arms opposite to those actuated by the force applying means, and a pressure element supported between the ends of the arms carrying the work applying elements and selectively secured to one of said arms to be operated therewith and in advance thereof for applying a predetermined pressure between the pieces to be engaged by the work applying elements before and during the working operation.

4. In a force applying tool, a pair of parallel plates each having an inwardly'extending annular flange in spaced aligned relation, the inner peripheries of said flanges lying on a common center, spool means disposed-between said plates on the center line of said flanges, means securing each of said plates to said spool means, a pair of rockable arms disposed between said plates and each having outwardly arcuate bosses formed thereon intermediate the ends thereof, sleeve means on said plates engaging the inner surfaces of said annular flanges, the inner periphery of said arm bosses being rockably sup-ported on said spool means and the outer periphery of said arcuate arm bosses being in sliding engagement with the inner periphery of said sleeve means, force applying means disposed between the ends of said arms on one side of the supporting plates therefor for moving the ends away from each other when moving the opposite ends of the arms toward each other with a predetermined pressure, work applying elements disposed on the ends of the arms opposite to that actuated by the force applying means, and cam means adjustably supported by said plates and disposed between said rockable arms on the opposite side of said spool means from said work applying means adapted to be rotated to limit the opening and closing movement of one of said rockable arms.

5. In a force applying tool, a pair of parallel plates each having an inwardly extending annular flange in spaced aligned relation, the inner peripheries of said flanges lying on a common center, spool means disposed between said plates on the center line of said flanges, means securing each of said plates to said spool means, a pair of rockable arms disposed between said plates and each having outwardly extending arcuate bosses formed thereon intermediate'the ends thereof, sleeve means on said plates engaging the inner surfaces of said annular flanges, the inner pedetermined pressure, work applying elements disposed on the ends of the arms opposite to that actuated by theforce applying means, a pressure element supported between the ends of the arms carrying the work applying elements and selectively secured to one of said arms to be operated therewith and in advance thereof for applying a predetermined pressure between the pieces to be engaged by the work applying elements before and during the work operation, and cam means adjustably supported by said plates and disposed between said rockable arms on the opposite side of said spool means from said pressure element adapted to be rotated to limit the opening and closing movement of one of said rockable arms.

6. In a force applying tool, a pair of parallel plates each having an inwardly extending annular flange in spaced aligned relation, the inner peripheries of said flanges lying on a common center, spool means disposed between said plates on the center line of said flange, means for releasably securing each of said plates to said spool means, sleeve means positioned between said plates engaging the inner surfaces of said annular flanges, a pair of rockable arms disposed between said plates each having outwardly extend-ing arcuate bosses formed thereon intermediate the ends thereof, the inner periphery of each of said arcuate bosses being rockably supported on said spool means and the outer periphery of each of said arcuate bosses slidably engaging the inner periphery of said sleeve means, force applying means disposed between the ends of saidarms on one side of the supporting plates therefor for moving the ends away from each other when moving the opposite ends of the arms toward each other with a predetermined pressure, work applying elements on the ends of the arms opposite to that actuated by the force applying means for performing a Work operation, mounting mean for said device, and resiliently actuated plunger means mounted within said lastnamed means and adapted to engage one of said rockable arms at a predetermined point during the opening of the latter to limit the movement of said arm while allowing said other arm to continue its movement.

I OTTO MUELLER.

References Cited in the flle of this patent UNITED STATES PATENTS Number Name Date 335,976 Thomson Feb. 9, 1886 615,547 Graves Dec. 6, 1898 696,235 Greenwood Mar. 25, 1902 1,301,883 Strom Apr. 29, 1919 1,401,777 Heidt "Dec. 27, 1921' FOREIGN PATENTS Number Country Date 1,371 Great Britain May 22, 1871 17,520 Great Britain Sept. 14, 1894 14,960 Great Britain July 23, 1901 485,405 Great Britain May 19, 1938