US3827382A

US3827382A - Method and apparatus for forming normally appearing stitches

Info

Publication number: US3827382A
Application number: US00299945A
Authority: US
Inventors: Vita R De; A Dorosz; H Scaletti
Original assignee: USM Corp
Current assignee: USM Corp
Priority date: 1972-10-24
Filing date: 1972-10-24
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: CA987965A; GB1446238A

Abstract

In a sewing machine having thread stitch forming instrumentalities for forming successive stitches in a workpiece and having means for moving the workpiece in vector directions and wherein the stitch forming instrumentalities may produce stitch abnormalities in at least one of the vector directions of workpiece movement, a method of forming normally appearing stitches by tensioning the stitch forming thread in response to the vector direction of workpiece movement. The method may also include drawing the stitch abnormalities into the workpiece. Apparatus for carrying out the foregoing method has means responsive to the vector direction of workpiece movement for controlling variable thread tensioning means included in the stitch forming instrumentalities.

Description

United States Patent 1 91 1111 3,827,382

De Vita et al. 1 Aug. 6, 1974 [54] METHOD AND APPARATUS FOR FORMING 917,886 9/1954 Germany 1 12/255 NORMALLY APPEARING STITCHES [75] Inventors: Raymond A. DeVita, Hamilton; Primary Examiner-Werner H. Schroeder Adolph S. Dorosz, Beverly; Henry Attorney, Agent, or Firm-Ralph D. Gelling; Vincent M. Scaletti, .ir., Wenham, all of A. White; Richard B. Megley Mass. 1

[73] Assignee: USM Corporation, Boston, Mass.

[22] Filed: Oct. 24, 1972 [2]] Appl. No.: 299,945

[ 5 7 ABSTRACT In a sewing machine having thread stitch forming instrumentalities for forming successive stitches in a workpiece and having means for moving the work- [52] US. Cl Ill/2 1 12 1 55 piece in vector directions and wherein the stitch forml l D053) D051) /0 ing instrumentalities may produce stitch abnormalities [58] Field of Search 112/2, 77, 79, 102, 103, in at least one of the vector directions of workpiece 112/117, 118, 119, 121.12, 181, 185, 203, movement, a method of forming normally appearing 262 stitches by tensioning the stitch forming thread in response to the vector direction of workpiece move- [56] References Cited ment. The method may also include drawing the stitch UNITED STATES P T abnormalities into the workpiece. Apparatus for carry- 1 ()81 596 12/1913 Finch 112 255 x ing out the foregoing method has mews responsive to 3,082,722 3/1963 Tateishi 112/181 the Vector direction of workpiece movement for 3,528,379 9/1970 Miller 112/254 X trolling variable thread tensioning means included in 3,724,409 4/1973 Olney, Jr. 112/255 the stitch forming instrumentalities.

FORElGN PATENTS OR APPLICATIONS 1,902,711 8/1970 Germany 112/255 6 Claims, 4 Drawing Figures FAIENTEBMIG 3.827. 382

SHEEI 1 0F 2 Pmmzmm: mm 3.827, 382

SHEEI 2 [IF 2 J8 L53 1 l Xi Yi I Point Daia Call 517M 54 HITEN fsiiil HT I J6 Tension Data BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for forming normally appearing stitches with thread.

Efforts to automate sewing machines and other stitch forming devices have recently increased as the cost and difficulty of obtaining skilled sewing machine operators has increased. Many of these efforts at automating sewing operations such as those described in copending U. S. Pat. No. 3,742,879 granted July 3, 1973, in the names of Hans F. Schaefer, Jr. and Reade Williams, have included means for automatically moving a workpiece relative to stitch forming instrumentalities of the sewing machine.

The means for moving a workpiece described in the above application differ from those traditionally employed in sewing machines in that the unidirectional, reciprocating workpiece moving means or feed dogs traditionally employed are replaced by means for moving the workpiece in multiple vector directions, usually along substantially orthogonal coordinates designated X and Y. The new workpiece moving means may be appropriately and automatically controlled to cause relative motion between the workpiece and stitch forming instrumentalities along a predetermined path which may include all vector directions relative to the stitch forming instrumentalities within the plane defined by the orthogonal coordinates. In contrast, the feed dogs and manual control traditionally employed in sewing machines produce relative movement between a workpiece and the stitch forming instrumentalities having vector directions essentially tangential to the path being sewn.

As further described in copending U. S. application Ser. No. 192,288 filed Oct. 26, 1971 in the name of Hans F. Schaefer, Jr., movement of the workpiece relative to stitch forming instrumentalities along a wide range of vector directions may produce stitch abnormalities evidenced by an extra twist or half-hitch in the completed stitch. Accordingly, this problem is called half-hitching. The half-hitch gives a canted, abnormal appearance to the completed stitch.

A further problem resulting from the wide range of vector directions of workpiece movement is variably increased binding or snagging of the stitch forming thread in certain vector directions of workpiece movement. As the workpiece is moved relative to the stitch forming instrumentalities, the stitch last formed in the workpiece draws thread from storage spools associated with the instrumentalities in a direction having a vector component in the direction in which the workpiece has carried the last formed stitch. In certain of these directions, the thread is drawn into frictional engagement with a side of a needle included in the stitch forming instrumentalities. Frictional engagement of the needle and thread binds the thread against movement from the storage spools and may prevent other stitch forming instrumentalities from forming a normally appearing stitch. Similarly, a half-hitch formed in the stitch will bind in a hole in the workpiece formed by the needle to strongly resist being drawn into the workpiece. On the other hand, where such binding does not occur, increased thread tension intended to overcome binding where it occurs may destroy a stitch originally normally formed by drawing it completely through the workpiece, giving an abnormal appearance. Accordingly, these problems are called thread binding. Both halfhitching and binding are stitch abnormalities.

SUMMARY OF THE INVENTION tus for carrying out the foregoing method has means responsive to the vector direction of workpiece movement between a selected pair of stitches for controlling variable thread tensioning means included in traditional stitch forming instrumentalities.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention which is intended to illustrate and not to limit the invention will now be described in relation to drawings of the embodiment, in which:

FIG. 1 is a perspective view of an automatically controlled sewing machine having means for practicing the invention;

FIG. 2 is a perspective view of the machine in FIG. 1 showing in enlarged scale elements embodying a portion of the invention;

FIG. 3 is a graphical illustration of a control function of the invention; and

FIG. 4 is a flow diagram of a control function of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment illustrated in FIG. 1 has a sewing machine generally at 10 similar, except as hereinafter described, to well known, commercially available electrically powered lockstitch or chain stitch sewing machines. The sewing machine includes stitch forming instrumentalities generally at 12 of the type well known in the art including a needle 14 for periodically penetrating a workpiece l6 and carrying thread (not shown) through the workpiece to form a series of stitches 18 in the workpiece.

Apparatus generally at 20 for moving the workpiece relative to the sewing instrumentalities differs from that traditionally employed with sewing machines in that the traditional feed dogs are replaced by a workpiece support 22 mounted generally normally to a longitudinal axis of the needle for movement relative to the sewing instrumentalities on a rack 24 engaged by an electrically driven pinion 26 operatively mounted on another, generally orthogonal pinion driven rack (not shown).

A control generally at 28 is appropriately connected to the electrical drive means for the pinions of the workpiece moving apparatus to control driving movement of the pinions. Appropriate control of the pinion driving means may then produce movement of the workpiece 16 relative to the needle 14 along vector directions extending 360 about the plane of the workpiece on the support 22. Movement about the plane of the workpiece support 22 iis conveniently dimensioned according to orthogonal X and Y coordinate axes superimposed on the support and corresponding to directions of movement implemented by each of the generally orthogonal racks of the workpiece moving means. As with a conventional sewing machine, each workpiece movement is followed by stitch forming penetration of the workpiece by the needle to form a succession of thread stitches divided by needle penetration points on the workpiece.

The sewing machine generally at also differs from traditional sewing machines in the provision of means generally at 30 for variably tensioning thread passing through the needle. As better seen in FIG. 2, the variable thread tensioning means comprise a thread tensioning device 32 linearly actuatable by a plunger 34 to provide either of two preselected tensions to a thread (not shown) wrapped about the tensioning device. Such tensioning devices and other variable thread tensioning devices are well known in the art and commercially available. A bell crank 36 is pivotally secured to a frame of the sewing machine and positioned to drive the plunger 34 against the action of a return spring in the device 32 into one of two thread tension selecting positions of the plunger 34. A rod 38 of a linear actuator 40 engages another arm of bell crank 36 to pivot the bell crank for driving the plunger 34. The linear actuator 40 may be an electrical solenoid for a pneumatic piston and cylinder, many types of which are well known in the art and commercially available. The actuator 40 is appropriately connected to the control 28 to operatively drive the tension setting plunger 34 in response to a signal from the control 28.

The two tensions provided the needle thread by tensioning device 32 are preselected to appropriately cooperate with other well known thread tensioning means of the stitch forming instrumentalities generally at 12, such as lever and cam or rotary thread take-up devices. These tensioning means of the stitch forming instrumentalities draw a last-formed stitch tightly against a workpiece to form a secure stitch by tensioning the thread forming a stitch in the workpiece l6 and running through the needle 14 to the thread tensioner 32 and back to its storage spool (not shown). If the thread tension device 32 provides a low tension, the thread takeup will draw more thread from the spool and apply a lower tension to the thread at the workpiece 16. On the other hand, if the thread tension device 32 provides a high tension, less thread can be drawn from the spool and a higher tension will be applied to the thread at the workpiece.

Then, according to the method of the invention, a high tension is applied when the stitch forming instrumentalities form a stitch abnormality such as a halfhitch to draw the half-hitch into the workpiece. The tension is preselected to draw the half-hitch interior of the workpiece, lodging it in the needle hole, so as to make the half-hitch invisible and to give the visible portion of the stitch a normal appearance. Similarly, a high tension on the thread from thread tension device 32 permits the thread to be drawn against binding of the thread on the needle to produce a tight, normally appearing stitch. On the other hand, where there is no half-hitching or binding, a lower tension is provided by the thread tensioning device 32 to permit normal formation of a stitch with normal appearance without drawing the stitch completely through the workpiece as would result with the higher tension. Accordingly, normally appearing stitches are formed whether the stitch forming instrumentalities form half-hitches, bind against the thread, or do neither.

The control 28 controls the variable thread tensioning device 32 to provide an appropriate tension for each stitch formed by the stitch-forming instrumentalities of the sewing machine. In the preferred embodiment the control 28 is an appropriately programed, commercially available, general purpose digital computer operatively associated with a commercially available numerical control. In the preferred embodiment the control 28 also functions to direct movement of the workpiece and therefore generates a pair of X Y coordinate values for each needle penetration point on the workpiece demarking the beginning and end points for each stitch. For example,

points

42 and 44 shown in FIG. 3 have coordinate values (X1, Y1) and (X2, Y2), respectively, relative to coordinate axes X and Y superimposed on the workpiece. However, in an alternative embodiment, shaft encoders operatively connected to the racks of the workpiece moving apparatus may provide point coordinate values as known in the art. The vector direction of workpiece movement for forming a stitch between the needle engaging points will be on a vector direction line 46 connecting the points. This vector will form an angle AG with a selected reference coordinate axis, here the Y axis. Similarly, angles 48 and 50 are predetermined to define zones of vector directions of workpiece movement which will not or will, respectively, cause the stitch forming instrumentalities to produce half-hitching and- /or binding. Accordingly, a predetermined higher or lower thread tension from the variable thread tensioning device 32 may be associated with each zone. Angles HT defining extremities of these zones are stored in the control 28 for reference.

Referring now to FIG. 4, a program for the control 28 generally at 52 includes a sub-routine 54 called HITEN which appears in the control program for the formation of each stitch. The main program portion 54 first calls the particular HITEN sub-routine 56. The HITEN sub-routine then calls the X Y coordinate axis values for the points beginning and ending the stitch, calculates the angle AG, and then calls for the angles HT defining the zones of vector directions associated with each tension to be applied by the tensioning device 32. The sub-routine compares the angle AG of the particular stitch with those defining the tension zones and determines which zone associated tension corresponds to the particular angle AG. It then provides an appropriate signal communicated to the linear actuator 40 to drive the tension device 32 into the tension position associated with the signal.

In accordance with the flow diagram, a particular program for the sub-routine HITEN provides a signal T equal to a logic zero for the lower tension position of the tension device 32 and a signal T equal to a logic one for the higher tension. Input parameters provided the sub-routine are a pair of X Y coordinate values for of the points beginning and ending a particular stitch and stored array of angle HT pairs defining zones of angles associated with each of the tension T signals. The particular sub-routine in block 56 of FIG. 4 then may be:

Sub-routine HITEN (X1, Y1, X2, Y2, HT, T) Dimension HT (4, 2)

DY Y2 Y1 AG ATAN (ABS (DY)/ABS (DX)) 1F (DX) 10, 20, 20 1F (DY) 11,12, 12 11 AG 180.+AG

Go to 22 12 AG 180.AG

Go to 22 IF (DY) 21, 23, 22 21 AG 360.-AG

Go to 22 23 IF (DX) 25, 25, 22

25 Write (1,100) 100 Format Error DX, DY 0) Go to 50 22 DO 1 1, Y

[F (AG l-lT (l, 1)) 30, 32, 31 31 IF (AG HT (1, 2)) 32, 32, 30 30 Continue Go to 50 32 T 1 50 Return End.

In alternative embodiments of the invention, the control 28 may be other than the above described general purpose digital computer and associated numerical control. For example, the control may be a special purpose digital computer or an analog computer appropriately programed as known by those skilled in the art to provide appropriate signals for the actuator 40. Similarly, the numerical control operatively associated with a computer, for example by reading a signal T for generating a signal for the actuator from an instruction medium such as punched or magnetic tape prepared by the computer, may be replaced by the general purpose digital computer itself. Preparation of such a numerical control tape may also be done manually in accordance with the teachings of the invention or by a separately located, tape preparing computer of one of the other above types. Still further, it will be appreciated that the control 28 could be a mechanical arrangement using cams or other devices to generate a signal appropriate for the linear actuator to drive the tensioning device 32. The latter mechanical arrangement may be particularly useful with sewing machines having mechanical workpiece guiding controls such as known bar tackers.

It will be appreciated that the particular thread tension for forming a particular stitch may be set prior to formation of the particular stitch, concurrently with the formation of the particular stitch or immediately after the formation of the particular stitch in accordance with the operation of the particular thread tension means in the stitch forming instrumentalities of a particular sewing machine. The timing of such tension setting in the program of the preferred embodiment may be selected by determining the position of the HITEN sub-routine in the main control program. It may be similarly set by appropriate organization of the other devices described as alternative embodiments of the control. Such sequence setting is well within the skill of the art.

Still further alternative embodiments, including, for example, more than two tension zones or more than two predetermined tension variations in the tensioning device, are contemplated to be within the scope of the invention defined by the following claims:

We claim:

1. A method of forming a normally appearing stitch with a thread in a relatively movable workpiece and thread, comprising the steps of: forming a stitch in the workpiece with the thread including controlling a vector direction of relative workpiece and thread movement; determining independently of controlling the movement the vector direction of relative movement; and controlling a tension of the thread in response to the determined direction of relative movement to form a normally appearing stitch.

2. A method as in claim 1 wherein the formed stitch has a stitch abnormality and additionally comprising the step of drawing the stitch abnormality into the workpiece.

3. A method as in claim 1 wherein the step of determining the vector direction of relative movement additionally comprises the step of determining when a stitch abnormality is formed.

4. In a sewing machine having thread, stitch forming instrumentalities including a device for variably tensioning the thread, and means for controlling movement of a workpiece relative to the stitch forming instrumentalities in vector directions, apparatus for forming a normally appearing stitch comprising: means independent of the control of movement means for determining the vector direction of relative movement means responsive to the determined vector direction of workpiece movement for controlling the variable thread tensioning device to form a normally appearing stitch.

5. A machine as in claim 4 wherein the stitch forming instrumentalities form a stitch abnormality and wherein the tension controlling means comprise means for drawing the abnormality into the workpiece.

6. A machine as in claim 4 additionally comprising means for determining when a stitch abnormality is formed.