US3553862A

US3553862A - Adjustable stretch frame for biaxially stressing sheet material

Info

Publication number: US3553862A
Application number: US792114*A
Authority: US
Inventors: Kaino J Hamu
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-01-17
Filing date: 1969-01-17
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12

Abstract

A STRETCH FRAME FOR BIAXIALLY STRESSING SHEET MATERIAL, SUCH AS PRINTING SCREEN, IN MUTUALLY PERPENDICULAR EDGEWISE DIRECTIONS. THE FRAME HAS A RECTANGULAR FRAME STRUCTURE MOUNTING FLOATING BARS FOR ATTACHMENT TO THE MARGINAL EDGES OF THE SHEET MATERIAL TO BE STRESSED, AND MEANS FOR INDEPENDENTLY ADJUSTING THE FLOATING BARS RELATIVE TO THE FRAME STRUCTURE TO STRESS THE SHEET MATERIAL IN MUTUALLY PERPENDICULAR EDGEWISE DIRECTIONS. THE MAJOR CONTRIBUTION OF THE INVENTION RESIDES IN THE SHEET GRIPPING STRUC-

TURE OF THE FLOATING BARS, WHEREBY A SHEET TO BE STRESSED MAY BE FIRMLY ATTACHED TO THE BARS AND YET READILY RELEASED FROM THE BARS, WHEN DESIRED.

Description

K. J. HAMU Jan. 12,1971

ADJUSTABLE STRETCH FRAME FOR BIAXIALLY STRESSING SHEET MATERIAL Filed Jan. 17, 1969 .nf w X a L KA/NO J HA/wu United States Patent 3,553,862 ADJUSTABLE STRETCH FRAME FOR BIAXIALLY STRESSING SHEET MATERIAL Kaino J. Hamil, 4013 N. Dnrfee Ave., El Monte, Calif. 91732 Filed Jan. 17, 1969, Ser. No. 792,114 Int. Cl. D06c 3/08 US. Cl. 38-402.]. 3 Claims ABSTRACT OF THE DISCLOSURE A stretch frame for biaxially stressing sheet material, such as printing screen, in mutually perpendicular edgewise directions. The frame has a rectangular frame structure mounting floating bars for attachment to the marginal edges of the sheet material to be stressed, and means for independently adjusting the floating bars relative to the frame structure to stress the sheet material in mutual- 1y perpendicular edgewise directions. The major contribution of the invention resides in the sheet gripping structure of the floating bars, whereby a sheet to be stressed may be firmly attached to the bars and yet readily released from the bars, when desired.

REFERENCE TO COPENDING APPLICATION Reference is made herein to my copending applica tion Ser. No. 699,492, filed Jan. 22, 1968, now Pat. No, 3,482,343 and entitled Frame For Stressing Sheet Material.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to handling devices for sheet material. More particularly, the invention relates to a stretch frame for biaxially stressing sheet material in mutually perpendicular edgewise directions.

Prior art As will appear from the ensuing description, the stretch frame of the present invention may be employed for various uses. The primary application of the frame, however, is in the silk screen printing industry for supporting printing screen, fabric, and the like in a taut condition. In this case, the frame is commonly referred to as a screen chase.

A variety of stretch frames for screen chases of the class described have been devised. These existing frames, however, are characterized by excessive complexity and cost of manufacture, difliculty of use, and various other undesirable features. My prior Pat. No. 3,482,343 discloses an improved stretch frame which avoids most if not all of these disadvantages of the earlier stretch frames. In general terms, the stretch frame of my prior patent comprises an open rectangular frame structure including mutually perpendicular frame members defining and bounding a central opening through the frame structure, floating anchor bars along the sides of this opening, means adjustably supporting the floating bars on their adjacent frame members for lateral adjustment of the bars relative to the frame members, and gripping means for attaching the marginal edges of the sheet material to be stressed to the floating bars. In use, a sheet of material to be stressed is secured along its marginal edges to the floating bars. These bars are then adjusted laterally outward to stretch the sheet in mutually perpendicular edgewise directions. The stretch frame embodies various other structural and functional features which represent advances over the existing prior art devices but which are unnecessary to elaborate on in the present disclosure.

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SUMMARY OF THE INVENTION The present invention provides a stretch frame of the general class described having improved floating bars for anchoring the marginal edges of the sheet material to be stressed. More particularly, the improvements of the invention reside in the sheet gripping structure of the floating bars. According to the present invention, this sheet gripping structure of each floating bar comprises an undercut channel which extends longtiudinally of and opens laterally through a slot in one side of the bar.

The channel is undercut in such a way as to form a flange-like portion along the normally outer edge of the slot through which the channel opens to the exterior of the bar. This flange portion provides a ledge within the channel which defines with the adjacent outer side wall of the channel an interior corner. Positioned within the channel are anchor rod means which are adapted to assume a sheet gripping position of wedging relation between the interior corner and the opposite, inner wall of the channel.

In use of the stretch frame, a marginal edge of the sheet material to be stressed is inserted through the channel of each floating bar in such a way that the marginal edge enters the channel along the inner edge of its slot, then passes around the underside of the anchor rod means Within the channel, and finally emerges from the channel along the outer edge of its slot. When the floating bars are adjusted laterally outward to stretch the sheet material edgewise, the anchor rod means assume their sheet gripping positions within their respective floating bar channels. In these positions, the marginal edges of the sheet material are firmly gripped between the rod means and the walls of the floating bar channels.

One advantage of the present invention resides in the fact that the anchor rod means of each floating bar is captivated within its channel and is thus not prone to dropping out of the channel in the event the stretch frame is inverted. Moreover, the anchor rod means tends to remain in a fixed position within its containing channel regardless of the position of the stretch frame and thus may be more readily manipulated to grip and release the sheet material to be stressed.

As will appear from the ensuing description, the improved stretch frame of the invention may utilize floating bar channels of various cross section and anchor rod means of various shapes and types. Two embodiments of the invention have been selected for illustrative purposes. In one of these disclosed embodiments, the anchor rod means of each floating bar comprises a pair of resiliently deformable anchor rods constructed of rubber or other suitable resilient material. When in sheet gripping position, these rods are wedged tightly between the interior corner and the inner wall of their containing floating bar channel in such a way that the rods are laterally compressed to firmly grip the sheet material between the rods and the walls of the channel. When engaging and releasing the marginal edge of the sheet material with the floating anchor bar, one of these anchor rods is removed. Removal of this rod is accomplished by stretching the latter lengthwise to reduce its lateral dimension sufficiently to enable the rod to pass from its containing channel through the channel slot.

In a second disclosed embodiment of the invention, the sheet gripping structure of each floating anchor bar comprises a single anchor rod. This rod is laterally dimensioned in such a way that when in sheet gripping position, it engages the wall of its respective floating bar channel at three positions to effect firm gripping engegement with the marginal edge of the sheet material to be stressed. In both forms of the invention, the anchor rods are captivated within their containing channels and thus do not tend to drop out of the channels when the frame is inverted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary top plan view of an improved stretch frame according to the invention;

FIG. 2 is an enlarged section taken on line 2-2 in FIG. 1;

FIG. 3 is an enlarged cross section through a floating anchor bar of the stretch frame illustrating the sheet gripping structure of the floating bar in its sheet releasing position;

FIG. 4 is a section similar to FIG. 3 illustrating the sheet gripping structure of the floating bar in its sheet gripping condition; and

FIG. 5 is a section similar to FIGS. 3 and 4 through a modified floating bar configuration for the stretch frame.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turing first to FIGS. 1 through 4 of these drawings, there is illustrated a stretch frame according to the invention. This stretch frame includes a rectangular frame structure 12 having a pair of side frame members 14 joined at their ends by a pair of end frame members 16. Only one of these end frame members is shown. In the particular embodiment of the invention illustrated, the side frame members 14 and end frame members 16 are simply welded to one another. If desired, however, these frame members may be joined in various other ways as, for example, in the manner disclosed in my copending application Ser. No. 699,492. The frame structure defines a central rectangular opening 18 bounded by the

frame members

14 and 16.

In addition to the frame structure 12, the stretch frame 10 includes four

floating anchor bars

20 and 22. The anchor bars 20 extend along the side frame members 14. The anchor bars 22 extend along the end frame members 16. Each

anchor bar

20 and 22 is supported on its

adjacent frame member

14 or 16 by adjusting means 24. This adjusting means is operable to move the respective anchor bar laterally inward toward and outward away from the frame opening 18. Each

anchor bar

20, 22 embodies gripping means 26 for releasably gripping the adjacent marginal edge of the sheet material 28 to be stressed. The major contribution of the present invention resides in the unique construction and arrangement of this sheet gripping means.

Briefly, in use of the stretch frame 10, the floating bar adjusting means 24 are operated to adjust the floating anchor bars 20, 22 laterally inward toward the frame opening 18. The marginal edges of the sheet material 28 to be stretched are then attached to the floating bars by their respective sheet gripping means 26. After proper attachment of the sheet to the floating bars has been accomplished, the bars are adjusted laterally out away from the opening 18 to biaxially stress the sheet material in its edgewise directions.

Referring now in greater detail to the drawings, each

frame members

14 and 16 has a generally channel shape in transverse cross section and includes a pair of inner and

outer flanges

30 and 32 joined by an intervening web 34. The upper edges of the outer frame flanges 32 are disposed substantially in a common plane which is located at a slightly higher elevation than the upper edges of the inner frame flanges 30.

The floating anchor bars 20, 22 comprise rigid elongate bar members of generally rectangular cross section. These floating bars may be'constructed of metal, plastic, wood or other suitable materials. As shown best in FIG. 2, each floating bar is positioned within the upwardly opening channel of its

respective frame member

14 or 16, between the inner and outer frame flanges .30, 32. The bar extends lengthwise Qf the channel, generally parallel to the frame flanges. Each floating bar embodies the sheet gripping means 26, referred to earlier. The sheet gripping means will be described in detail presently.

The illustrated floating bar adjusting means 24 comprise lead screws 36 extending normal to the

frame members

14, 16 through the floating bar receiving channels in these members. Referring to FIG. 2, it will be observed that each lead screw 36 has a reduced inner end 38 which is journalled within a bore 40 in the corresponding inner frame flange 30. The outer end of each lead screw extends through and is journalled in the respective outer frame flange 32. Rigid on the outer end of each lead screw is a polygonal head 42 by which the screw may be rotated. Each lead screw is equipped with thrust bearing means 44 which permit the screw to rotate by strain the screw against axial movement. In the particular embodiment of the invention illustrated, this thrust bearing means comprises a pair of washers 46 on the lead screw at opposite sides of the outer frame flange 32 and a cross pin 48 which extends through the lead screw just endward of the inner washer. Each floating

anchor bar

20, 22 is equipped with a number of adjusting lead screws 36. The adjusting screws for each anchor bar are uniformly spaced along the bar. Each lead screw extends through and is threadedly engaged with its respective bar. It is now evident, therefore, that rotation of the lead screws 36 for each floating

anchor bar

20, 22 adjusts the corresponding bar laterally inward toward or laterally outward away from the frame opening 18, depending upon the direction of rotation of the lead screws.

As noted earlier, the present invention is primarily concerned with the construction and arrangement of the sheet gripping means 26 of the floating anchor bars 20, 22. For the sake of ready reference in the ensuing description, it will be observed that each floating bar has inner and

outer sides

50 and 52 and an upper intervening side 54. In general terms, the sheet gripping means 26 of each anchor bar comprise a longitudinal channel 56 opening laterally through a longitudinal slot 58 in the upper intervening side 54 of the anchor bar. The channel has inner and

outer side walls

60 and 62. As shown best in FIGS. 2 through 4, the channel is undercut in such a way as to provide the floating bar with a flange-like portion 64 along the intervening side 54 of the bar. This flange portion projects inwardly from the outer channel side wall 62 toward the inner channel side wall 60 to define the channel slot 58 between the inner edge of the flange portion and the inner channel side wall. The flange portion 64 forms within the channel 56, along the outer edge of its slot 58, a ledge 66. This ledge defines with the outer channel side wall 62 and intervening interior corner 68.

In addition to the channel 56, the sheet gripping means 26 of each floating

anchor bar

20, 22 comprises anchor rod means which extends longitudinally through the channel. This anchor rod means is laterally dimensioned to assume within the channel 56 a sheet gripping position, shown in FIG. 4, wherein the rod means is disposed in wedging relation between the interior channel corner 68 and the inner channel side wall 60. The sheet material 28 to be stressed is inserted through the channel 56 in such a way that the sheet enters the channel along the inner edge of its slot 58, then extends around the underside of the anchor rod means 70, and finally emerges from the channel along the outer edge of its slot. The sheet gripping means 26 of each anchor bar is thus constructed and arranged in such a way that the sheet 28 is firmly gripped between the anchor rod means 70 and the walls of the anchor bar channel 56.

In the particular embodiment of the invention selected for illustration in FIGS. 1 through 4, the inner wall 60 of the channel 5-6 in each floating

anchor bar

20, 22 has an upper convex portion adjacent the channel slot 58. and a lower concave portion which merges tangentially with the convex portion. The outer channel side wall 62 has an upper concave portion which defines the interior channel corner 68 and a lower concave portion which merges tangentially with the lower concave portion of the inner side wall 60 to provide the channel 56 with a generally semi-cylindrical bottom portion. The upper extremity of the upper convex portion of the inner channel side Wall 60 curves inwardly and then downwardly to merge tangentially with the inner side face 50 of the floating bar. There is thus defined on the floating bar, along the inner edge of the channel slot 58, a rounded lip 72. As shown best in FIG. 2, the upper edge of this lip is substantially tangent to the plane containing the upper edges of the inner frame flanges 30. The upper extremity of the upper concave portion of the outer channel side wall 62 extends inwardly to define the ledge 66 and to intersect, at approximately right angles, the inner edge of the anchor bar flange portion 64. It will be observed that this flange portion is located at a somewhat higher elevation than the inner anchor bar lip 72 and that the upper surface 54 of the flange portion is located substantially in the plane containing the upper edges of the outer frame flanges 32.

The anchor rod means 70 of the illustrated embodiment comprises a pair of generally cylindrical, resiliently de formable

anchor rods

74 and 76. These rods may be constructed of rubber or other suitable resiliently deformable material. The

anchor rods

74, 76 are generally symmetrical about their longitudinal axis and, in this instance, are cylindrical in cross section. The two rods have approximately the same diameter as the lower cylindrical portion and the upper interior corner 68 of the anchor rod channel 56. The center spacing between the axes of the lower cylindrical portion and the upper interior corner of the channel 56 is slightly less than diamerter or each anchor rod.

From the foregoing description, it is evident that the

anchor rods

74, 76 of each floating

anchor bar

20, 22 are adapted to assume their sheet gripping positions of FIG. 4 within the anchor rod channel 56. In these positions, the lower rod seats within the lower cylindrical portion of the channel, the upper rod seats within the upper interior channel corner 68, and the rods are laterally compressed, a shown. A feature of the invention resides in the fact that the Width of the channel slot 58 is slightly less than the diameter of each

anchor rod

74, 76. It is evident, therefore, that the anchor rods are effectively captivated within the channel.

In use of the stretch frame 10, the anchor bar adjusting screw 36 are rotated in a direction to adjust the floating anchor bars 20, 22 laterally inward toward the frame opening 18. The upper anchor rod 74 in each anchor bar is then removed. This removal of the anchor rod is accomplished by stretching the rod lengthwise to reduce its lateral width or diameter sufficiently to enable the rod to pass through the anchor rod slot 58. The lower anchor rod 76 is then moved upwardly out of the cylindrical bottom portion of the anchor bar channel 56 and the adjacent marginal edge of the sheet material 28 to be stressed is passed through the slot and around the underside of the anchor rod 76, in the manner illustrated in FIG. 3. The upper anchor rod 74 is then inserted back into the channel and wedged between the channel corner 68 and the lower anchor rod 76. The marginal edge of the sheet material 28 is thereby firmly gripped between the

anchor rods

74, 76 and the

walls

60, 62 of the channel. After the four corners of the sheet 28 have thus been firmly anchored to the anchor bars 20, 22, the anchor bar adjusting screws 36 are rotated in the opposite direction to adjust the bars laterally outward away from the frame opening 18. This outward adjustment of the anchor bars stresses the sheet material 28 in mutually perpendicular edgewise directions. When thus stressed, the sheet material extends inwardly from each anchor bar over the inner rounded lip 72 of the bar and over the upper edge of the adjacent inner frame flange 30.

Turning now to FIG. 5, there is illustrated a modified 6 sheet gripping means 26a which may be utilized in the stretch frame 10 of FIGS. 1 through 4, in lieu of the sheet gripping means 26. In this case, each anchor rod channel 56a has generally flat inner and outer side walls 60a, 62a. The outer side wall 62a generally parallels the inner and outer side faces 50, 52 of the anchor bar. The inner channel side wall 60a slopes outwardly at a slight angle toward the outer side wall 62a in the direction of the channel slot 58a. The upper extremity of the inner side wall then curves inwardly andl downwardly to merge tangentially with the inner side face of the anchor bar and to define a rounded lip 72a along the inner edge of the channel slot. The ledge 66a formed by the flange portion 64a of the anchor bar extends generally normal to the outer channel wall 62a.

Contained within each anchor bar channel 56a is a single anchor rod 74a. This anchor rod is generally symmetrical about its longitudinal axis and, in this instance is circular in cross section. The rod is laterally dimensioned to have a snug fit between the inner and outer channel sidewall a, 62a at the point of their closest approach, adjacent the inner anchor bar lip 72a. It will be observed that the anchor rod 74a is adapted to assume a sheet gripping position wherein the rod engages the other channel sidewall 62a at A, the ledge 66a at B, and the inner channel sidewall 60a at C. In its sheet gripping position, therefore, the anchor rod has a three point contact with the walls of its containing anchor bar channel 56a.

The stress frame 10, when equipped with the sheet gripping means 26a, is used in much the same way as described earlier in connection with FIGS. 1 through 4. Thus, when initially attaching the sheet material 28 to be stressed to the anchor bars 20, 22, there bars are adjusted inwardly toward the frame opening 28. The anchor rods 74a in the anchor bars are then moved downwardly in their containing anchor bar channels 56a to the wide bottom portions of the channels. In these positions of the anchor rods, sufficient clearance is provide between the rods and the walls of the channels to permit the marginal edges of the sheet 28 to be inserted through the channels and around the underside of the anchor rods, in the manner illustrated. The anchor rods are then moved out- Wardly to their gripping positions of FIG. 5 within their containing anchor bar channels. In these positions, sheet gripping means 26a grip the marginal edges of the sheet at the three points A, B, and C.

It is significant to note here that the diameter of each anchor rod 74a is greater than the width of its anchor bar channel slot 58a. Accordingly, the anchor rods are captivated within their containing channels. In addition, it Will be observed that the tension or stress in the sheet 28 tends to pull the anchor rods 74a upwardly in their containing channels 56a against the channel ledges 66a. This prevents the anchor rods from being pulled out of their channels and also urges the rods into firm gripping engagement with the portions of the sheet 28 which extend between the rods and the channel ledges 66a.

As noted earlier, the anchor rods 74a may have various cross sectional configurations. The referred configuration is the cylindrical configuration illustrated. However, the anchor rods could have a polygonal shape in cross section or any other cross section, preferably one which is symmertical about the longitudinal axis of the rods.

What is claimed as new in support of Letters Patent is:

1. A frame for biaxially stressing sheet material in mu,- tually perpendicular edgewise directions, comprising:

a generally rectangular frame structure having a central rectangular opening and including side and end frame members along the sides and ends of said opening,

elongate anchor bars extending along said frame members, respectively,

adjusting means connecting said anchor bars and frame members for laterally adjusting said anchor bars inwardly toward and outwardly away from said openeach anchor bar having an inner side adjacent said opening, an outer side remote from said opening, and an intervening side,

each anchor bar having gripping means, said gripping means comprising an undercut longitudinal channel opening laterally through a longitudinal slot in said intervening side of the respective anchor bar, said channel having inner and outer side walls and the anchor bar having a flange portion along said intervening side thereof which projects inwardly from said outer channel side wall toward said inner channel side wall to define said slot between the inner edge of said flange portion and said inner side wall, said flange portion forming within said channel along the outer edge of said slot a ledge which faces the bottom of said channel and defines with said outer channel side wall an intervening interior corner, anchor rod means within and extending longitudinally of said channel, said channel being adapted to receive a marginal edge of said sheet material in a manner such that said sheet material enters said channel along the inner edge of said slot, then extends around the underside of said rod means between the latter and the walls of said channel, and finally emerges from said channel along the outer edge of said slot, and said rod means being laterally dimensioned to assume a sheet gripping position within said channel wherein said rod means is disposed in wedging relation between said corner and said inner channel side wall, whereby said sheet is gripped between said rod means and the walls of said channel,

said anchor rod means comprising a pair of separate resiliently deformable anchor rods disposed side by side within said channel, and

said rods being laterally compressed when in said sheet gripping position.

2. A frame for biaxially stressing sheet material in mutually perpendicular edgewise directions, comprising:

a generally rectangular frame structure having a central rectangular opening and including side and end frame members long the sides and ends of said openelongate anchor bars extending along said frame members, respectively,

said anchor rod means comprises a cylindrical anchor rod,

said channel side walls converge in the direction of said slot, said anchor rod is laterally dimensioned to have a wedging fit between said side walls when in said sheet gripping position, and said channel being substantially deeper than the cross sectional dimension of said anchor rod whereby said rod may move to a sheet releasing position in the bottom of said channel.

3. A frame for biaxially stressing sheet material in mutually perpendicular edgewise directions, comprising:

elongate anchor bars extending along said frame members, respectively,

the bottom of said channel and said interior channel corner each having a generally semi-circular configuration in transverse cross section,

said anchor rod means comprising a pair of generally cylindrical resiliently deformable anchor rods having approximately the same diameter as said bottom channel portion and said interior corner,

the center spacing between the axes of said bottom channel portion and said interior corner being less than the diameter of each anchor rod, and

said anchor rods when in said sheet gripping position being disposed side by side with one rod seating within said channel bottom portion and the other rod seat- 9 10 ing within said interior channel corner and the rods 2,893,162 7/ 1959 Knowles 38--102.1 being laterally compressed between the channel walls. 3,422,554 1/ 1969 Prinzhorn 38102.1

References Cited FOREIGN. PATENTS UNITED STATES PATENTS 5 519,040 4/ 1953 Belgmm 38102.1 1,335,806 4/ 1920 Trueb -2 38-10291 PATRICK D. LAWSON, Primary Examiner