US3760695A

US3760695A - Resilient piston stop construction

Info

Publication number: US3760695A
Application number: US00230569A
Authority: US
Inventors: R Rothfuss
Original assignee: Senco Products Inc
Current assignee: Senco Products Inc
Priority date: 1972-03-01
Filing date: 1972-03-01
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25
Also published as: JPS4899776A; NL7302536A; DE2303536A1

Abstract

Resilient structure for stopping a high energy piston in short distance at the end of its stroke without generating excessive heat and without exceeding the elasticity of the components. The structure includes two identical resilient members, one disposed in the end of the cylinder and the other carried on the underside of the piston. The member carried by the piston may be used to resiliently, detachably secure a working member to the piston.

Description

United States Patent Rothfuss Sept. 25, 1973 [54] RESILIENT PISTON STOP TI N 3,320,860 5/1967 Bade 92/85 x 3,600 10 68 B 92 85 x 75 Inventor: Robert G. Rothiuss, Cincinnati, Ohio 19 ade ASSigneeI Senco ts, at Primary ExaminerMartin P. Schwadron Ohio Assistant ExaminerAbe Hershkovitz M 1 Attorney-John Melville et a].

21 1 Appl. No.: 230,569

[57] ABSTRACT Resilient structure for stopping a high energy piston in V 5" d z gg short distance at theend of its stroke without generat- [58] "55 88 209 ing excessive heat and without exceeding the elasticity 0 care of the components. The structure includes two identical resilient members, one disposed in the end of the [56] References Clted cylinder and the other carried on the underside of the UNITED STATES PATENTS piston. The member carried by the piston may be used 2,983,922 5/1961 Juilfs 92/85 X to resiliently, detachably secure a working member to 3 ,160,075 12/1964 Powers 92/85 x the piston 3,205,787 9/1965 Volkmann 92/85 X 3,231,255 H1966 Olson 92/85 UX 8 Claims, 2 Drawing Figures i i L r fi T w l 5 Ma Q RESILIENT PISTON STOP CONSTRUCTION BACKGROUND OF THE INVENTION This invention relates generally to a resilient piston stop and especially to a resilient structure for stopping a high energy piston in a very short distance. The invention has great and particular utility in connection with fluid actuated fastener driving devices, and accordingly the invention will be described in terms of such an embodiment Generally considered, fluid actuated fastener driving devices of the type under consideration all include a working cylinder having a piston slidably disposed therein. Upon the admission of suitable fluid power in the cylinder,.such as for example air under pressure, the piston is driven rapidly downwardly in a working stroke. A fastener driver carried by the piston is effective during the working stroke to drive a fastener fully into a workpiece.

Early fastener driving devices such as shown for example in U.S. Pat. No. 2,585,939 in the name of A. G. Juilfs, issued on Feb. 19, 1952, disclose the use of a spring for returning the piston to its original position upon completion of the working stroke. That is, the space in the working cylinder above the piston was vented to atmosphere, and a conventional spring was effective to move the piston upwardly in a return stroke. With tools of this type, the provision of a suitable piston stop did not present a significant problem. In the first place, the early tools were relatively small and hence the piston did not develop great energy. Secondly, the entire working stroke of the piston was against the force of the spring, and this too tended to retard the velocity of the piston. v

U.S."Pat. No. 2,983,922 in the name of A. G. Juilfs, issued on May 16, 1961, taught the use of a plenum type return system. In other words, at the conclusion of the working stroke of the piston, a portion of the air under pressure from the working cylinder was admitted into a return reservoir, and this air under pressure was utilized to return the piston in its upward stroke. In a sense, the elimination of the spring return system began to create the necessity for a suitable resilient piston stop in connection with a pneumatic fastener driving device.

It will further be appreciated by the skilled worker in the art that fluid actuated fastener driving devices today have become larger and more powerful. Numerous commercial tools are available which will satisfactorily drive. three inch staples, or d common nails into hard wood.

Under these circumstances, the problem of the provision of a suitable piston stop are greatly magnified. The power of these fastener driving devices is such that the driving resistance of the fastener upon penetration of the workpiece has relatively little effect in stopping the fastener. The final or fully driven position of the fastener is determined almost entirely by the relative position between the end of the fastener driver and the nose piece of the tool when the piston is at the bottom position. The piston stop assembly of course determines in part this relative position of the components.

In other words, in a fluid actuated fastener driving tool, the piston stop construction. must bring a very high energy piston to a full stop in the space of approxiprior art constructions are subject to extreme wear and rapid deterioration (if not total destruction) when utilized with high energy, more efficient fluid actuated tools.

Keeping the foregoing comments in mind, it is a primary object of this invention to provide a resilient structure for stopping a very high energy piston in a short distance at the end of its stroke.

It is a more specific object of the invention to provide such a structure which will stop a piston without generating excess heat and without exceeding the elasticity of the components. This of course results in greatly increased life and durability of the piston stop components.

SUMMARY OF THE INVENTION The resilient piston stop structure of this invention contemplates the provision of two identical resilient members. One of these resilient members is disposed in the bottom end of a working cylinder, and the other is carried on the underside of the working piston.

In a specific embodiment of the invention, the resilient component carried by the underside of the piston may be utilized to resiliently, detachably secure a working member to the piston.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view ofa fluid actuated fastener driving device including the resilient piston stop structure of this invention.

FIG. 2 is a cross sectional view of the device shown in FIG. 1 showing the working piston at the end of its working stroke.

DESCRIPTION OF THE PREFERRED EMBODIMENT As just indicated, FIGS. 1 and 2 illustrate a fastener driving too] including the resilient piston stop structure of this invention. The tool shown in these Figures is described in great detail in copending application Ser. No. 210,812 filed Dec. 22, 1971 in the names of Robert G. Rothfuss and Carl T. Becht. The tool does not per se form a part of this invention. Hence, it will be described only very briefly below.

The tool body includes a head portion indicated generally at 10, a rearwardly extending'handle portion indicated generally at 12, a nose piece or guide body indicated generally at 14, a magazine structure indicated generally at 16, and a manually actuated trigger 18.

Disposedwithin the head portion 10 is the main or the working cylinder sleeve indicated generally at 20. Slidably disposed within the cylinder sleeve is the piston indicated generally at 22. By comparing FIGS. 1 and 2, it will be seen that the piston is movable from an initial position adjacent the top of the cylinder sleeve (FIG. 1) to a down position adjacent the other end of the cylinder sleeve (FIG. 2).-

The fastener driver indicated at 24 is carried by the piston, as will be explained in more detail hereinafter.

In operation, the tool will be connected in a conventional manner to a suitable source of fluid under pressure, in this case, compressed air. The magazine 16 will be loaded with a supply of fasteners in strip form which are urged by the magazine toward an internal passage or drive track 14a in the nose piece of the tool. As seen in FIG. 1, in the initial position the lowermost end of the driver 24 is disposed slightly above the head of the fastener positioned in the drive track 1421.

Upon actuation of the manual trigger l8, and as a consequence of valving structure which does not form a part of this invention, air under pressure will be admitted via the slots 26 into the cylinder sleeve above the piston 22. This air under pressure serves to rapidly drive the piston 22 and driver 24 downwardly in a working stroke to the position shown in FIG. 2. At this time, a portion of the air under pressure in the working cylinder is bypassed or conducted into a return reservoir for ultimate use in returning the piston.

In normal operation, release of the manual trigger 18 by the operator is effective to prevent further air under pressure from entering the slots 26, and to vent the upper portion of the cylinder sleeve 20 to atmosphere. At this time, air under pressure in the return reservoir is effective to act on the underside of the piston 22 and force it upwardly to the original position shown in FIG. 1.

Plenum type return systems in connection with fastener driving tools are shown in detail in US. Pat. No. 26,262 in the name of A. G. .luilfs, dated Sept. 5, 1967 and entitled Portable Stapler With Pneumatic Drive and Return". The specific valving structure and return operation of the device shown in this application are explained in detail in copending application Ser. No. 210,812 referred to earlier.

In the embodiment illustrated, the piston indicated generally at 22 includes the relatively light weight shell 28. The shell 28 may be made of aluminum or any other suitable material. The shell is provided on its outer periphery with a groove 28a which carries the O- ring 30 in order to maintain a sealing relationship with the cylinder sleeve 20 during both the drive and return strokes.

The underside of the piston shell 28 is provided with the counterbores 32 and 34 which receive the unitary driver assembly to be described hereinafter. The piston shell 28 isalso provided with the downwardly extending, annular skirt portion 36 which is undercut so as to provide an annular bead 38.

The unitary driver assembly briefly mentioned earlier comprises the driver 24, the central hub 40, and the hub mounting plate 42. As shown in the drawings, these are preferably three separate components which are secured together in any satisfactory manner so as to provide a unitary assembly. It will be apparent that the hub 40 and mounting plate 42 respectively are received in the counterbores 32 and 34 in the piston shell.

The resilient piston stop member 44 is provided with a central aperture 45 through which the driver 24 extends and with the annular groove 46 so that it will snap into place within the depending skirt 36 with the head 38 engaged in the groove 46. In this manner, the unitary driver assembly may be resiliently and detachably secured to the piston shell 28.

It will be observed that the upper surface of the member 44 is provided with the circular, semi-cylindrical relieved area 48. This is necessary in order to preventundue shearing acting caused by relative movement between the mounting plate 42 and the shell 28 during stopping.

Adjacent the bottom of the working cylinder, a second resilient piston stop member 50 is provided. The resilient member 50 is exactly identical to the member 44 but it is disposed upside down. That is, it is provided with a central aperture 51, an annular groove 52, and a circular, semi-cylindrical relieved area 54. When fitted into an appropriate cavity in the bottom of the tool casting or cylinder sleeve as the case may be, an annular bead will be engaged in the groove 52.

-The effective life of a resilient piston stop is believed to be determined by three primary characteristics. These are the load applied (in other words, the force exerted by the piston), the stopping distance (the distance between the first contact of the moving member and the final position of the moving member), and the amount of working" the resilient member undergoes. The amount of working of the resilient member is based largely on what may be called the shape factor. The shape factor, for purposes of this application, may be defined as the ratio of the loaded area of the member to the free area of the member. In the case of the embodiment illustrated, the ratio will be equal to the area of the impact face to the unconfined side wall area of the member plus the area of the central aperture.

It is very important to the success of this invention that the

resilient members

44 and 50 be substantially identical in size in order to divide the force and derive full benefit from the utilization of two separate resilient members.

In terms of fastener driving tool design, it will be assumed that a tool is to be built having a given piston diameter, piston velocity, and total force or energy. If stopping distance can be increased, resilient piston stop life can be increased by making a taller resilient member so that the working on the member is lessened. However, in the case of fastener driving devices, the

. stopping distance is also a fixed parameter. Under these described in this application, the total ratio of loaded area to free area of the resilient members is effectively doubled, and greatly increased piston stop life is possible.

It is believed that the foregoing constitutes a full and.

complete disclosure of this invention, and no limitations are intended except insofar as specifically set forth in the claims which follow.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a fastener applying device having a cylinder, a piston reciprocable in said cylinder a fastener driver, and means for moving said piston and fastener driver in a driving stroke to drive a fastener into a workpiece; an improved piston stop structure comprising:

first and second resilient members of substantially equal size, one of said members being fixedly mounted at the end of said cylinder, the other of said members being carried adjacent the side of said piston facing said one member, each said resilient member having a central aperture for the p'assage of said fastener driver, i

and the area of the impact face of each of said resilient members being equal to the unconfined side wall area plus the area of the central aperture of the respective resilient member.

2. The improved piston stop structure claimed in claim 1 including means for resiliently and releasably securing said other of said resilient means to said piston.

3. The improved piston stop structure claimed in claim 2 wherein said means for resiliently and releasably securing said other of said resilient members to said piston is effective to resiliently secure said fastener driver to said piston.

4. The improved piston stop structure claimed in claim 2 including a mounting plate secured to the upper end of said fastener driver, and wherein said fastener driver extends through said aperture in the other of said resilient members with said mounting plate against the surface of said other of said resilient members, whereby said means for securing said other of said resilient members to said piston is effective to resiliently secure said fastener driver to said piston.

5. In a device having a cylinder, a piston slidable in said cylinder, and means for driving said piston at high velocity toward one end of said cylinder; and improved piston stop structure comprising:

a. a first resilient member mounted at said one end of said cylinder;

b. a second resilient member carried by the side of said piston facing said one end of said cylinder, said first and second resilient members being substantially equal in size,

6. The improved piston stop structure claimed in claim 5 wherein the side of said piston facing said one end of said cylinder includes an annular depending skirt, a portion of said second resilient member being surrounded by said skirt.

member.

Claims

1. In a fastener applying device having a cylinder, a piston reciprocable in said cylinder a fastener driver, and means for moving said piston and fastener driver in a driving stroke to drive a fastener into a workpiece; an improved piston stop structure comprising: first and second resilient members of substantially equal size, one of said members being fixedly mounted at the end of said cylinder, the other of said members being carried adjacent the side of said piston facing said one member, each said resilient member having a central aperture for the passage of said fastener driver, and the area of the impact face of each of said resilient members being equal to the unconfined side wall area plus the area of the central aperture of the respective resilient member.

5. In a device having a cylinder, a piston slidable in said cylinder, and means for driving said piston at high velocity toward one end of said cylinder; and improved piston stop structure comprising: a. a first resilient member mounted at said one end of said cylinder; b. a second resilient member carried by the side of said piston facing said one end of said cylinder, said first and second resilient members being substantially equal in size, and the area of the impact face of each of said resilient members being equal to the unconfined side wall area plus tHe area of the central aperture of the respective resilient member.

7. The improved piston stop structure claimed in claim 6 wherein said skirt is undercut to provide an annular bead adjacent the free edge thereof, and wherein said second resilient member includes an annular groove engageable by said bead to resiliently secure said second resilient member to said piston.

8. The improved piston stop structure claimed in claim 6 including annular mounting means for said second resilient member, said mounting means confining only a portion of the side wall of said second resilient member.