United States Patent: 3698444

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United States Patent	3,698,444
Hindle , et al.	October 17, 1972

PNEUMATIC PICKING MECHANISMS

Abstract

A pneumatic picking motion for a weaving loom includes a linear-actuator comprising a piston movable in a cylinder under the influence of a measured change of compressed air applied thereto, the piston being connected with a picking-stick of the loom by means of a linkage. Preferably, the linkage is a compensating linkage arranged to provide uniformity of speed for the power-stroke of the piston.

Inventors:	Hindle; Thomas (Blackburn, EN), Banks; David Dugmore (Blackburn, EN)
Assignee:	Hindle Son and Company Limited (Blackburn, EN)
Appl. No.:	05/065,412
Filed:	August 20, 1970

Foreign Application Priority Data


Aug 23, 1969 [GB]			42134/69

Current U.S. Class: 139/142

Current International Class: D03D 49/00 (20060101); D03D 49/34 (20060101); D03d 049/34 ()

Field of Search: 60/57 139/144,142

References Cited [Referenced By]

U.S. Patent Documents


3114396	December 1963	Bardsley et al.
2488192	November 1949	Hindle
3191633	June 1965	Piot
2677933	May 1954	Hopkinson

Foreign Patent Documents


404,525	Oct., 1924	DD

Primary Examiner: Jaudon; Henry S.

Claims

What we claim is:

1. Pneumatically operable pickers for a loom wherein pickers are arranged at opposite ends of the loom to drive a shuttle across the loom from one shuttle box to the other, means for actuating the pickers to cause them to impel the shuttle comprising pneumatically operable, linearly movable, reciprocable actuators, means for supplying pressure to said pneumatically operable actuators comprising for each a heated container connected to a source of air pressure, said container having inlet and outlet ports connected respectively to said source and to the pneumatically operated actuator, closures associated with the respective ports, and means controlling said closures so that when the inlet to the container is open the outlet to the pneumatically operated actuator is closed and vice versa, and linkage operably connecting the actuators to the pickers to apply a driving force to the pickers during the driving part of their strokes.

2. Apparatus according to claim 1, wherein each pneumatically operable actuator comprises a cylinder and a piston slidable in the cylinder, the piston having a piston rod connected thereto and extending from the cylinder, and said linkage connecting the piston rod to the picker.

3. Apparatus according to claim 1, wherein the actuator is a cylinder and piston and the means for supplying pressure to the actuator is a container, the volume of which is approximately equal to the volume of that portion of the cylinder traversed by the piston during the driving part of its stroke.

4. Apparatus according to claim 2, comprising a valve box secured to one end of the cylinder, said valve box containing a first passage connecting the cylinder with the container, a second passage connecting the cylinder with an outlet, and valve means associated with each of said passages.

5. Apparatus according to claim 4, wherein the valve means comprise poppet-valves slidably mounted in the valve box and engageable with valve seats therein.

6. Apparatus according to claim 5, comprising servo-mechanisms operably connected to said poppet-valves and adapted upon actuation to effect displacement thereof.

7. Apparatus according to claim 6, comprising an electrically operable slide valve common to the servo-mechanisms of the poppet-valves adapted selectively to place such mechanisms in connection with a source of compressed air.

8. Apparatus according to claim 7, wherein the slide valve controlling the servo-mechanism of the valve means of said first and second passages is adapted to control the servo-mechanism of the air container inlet port.

9. Apparatus according to claim 4, wherein the passages contain valve seats and wherein the valve means in the second passage is operable for movement into engagement with its seat thereby to close such passage in advance of movement of the valve means in the first passage from its seat.

10. Apparatus according to claim 52, wherein the closure associated with the inlet port in the air container is a poppet-valve slidably mounted in the valve box.

11. Apparatus according to claim 10, wherein there is a servo-mechanism for controlling said poppet-valve.

12. Apparatus according to claim 52, wherein the closure associated with the inlet to the container comprises a one-way valve and a control valve is provided in the air feed to the one-way valve adapted selectively to apply pressure air thereto.

13. Apparatus according to claim 12, wherein the control valve comprises a slide valve operable also to control servo-mechanism operating on the valve means in the first and second passages in the valve box.

14. Apparatus according to claim 51, further including a pattern chain having bowls and spacers for controlling each actuator, an electrical circuit and a switch in said circuit controllable from the pattern chain, said circuit being adapted to control supply of compressed air to and from the actuator.

15. Apparatus according to claim 14, wherein said circuit further includes switch means operable by a timing cam thereby to insure operation of the required actuator at an appropriate time in the loom cycle.

16. Apparatus according to claim 14, wherein a further switch in the electrical circuit of each actuator sensitive to the condition of the actuator and operable at or slightly in advance of the completion of the driving impulse thereof.

17. Apparatus according to claim 1, wherein the actuators are controlled by an electrical circuit which includes position switches sensitive to the presence of the shuttle in a shuttle box, the circuit being adapted to vary the condition of a slide valve operating to actuate servo-mechanisms operating on valve means controlling the passage of air to or from the linear actuators.

18. Apparatus according to claim 16, wherein said electrical circuit further includes switch means operable by a timing cam to insure operation of the required actuator at an appropriate time in the loom cycle.

19. Apparatus according to claim 1, wherein the actuators comprise cylinders containing pistons, the latter being connected by piston rods to linkage and each cylinder is pivotally supported at the end opposite that from which the piston rod protrudes for angular movement above a fixed fulcrum.

20. Pneumatically operable pickers for a loom wherein the pickers are arranged at opposite ends of the loom to drive a shuttle across the loom from one shuttle box to the other, means for actuating the pickers to cause them to impel the shuttle comprising pneumatically operable, linearly movable, reciprocable actuators, means for supplying pressure to said pneumatically operable actuators to move them through a predetermined stroke in a direction to impart a driving force to the pickers and to return them to their initial positions, and linkage operably connecting the actuators to the pickers to apply a substantially uniform driving force to the pickers during the driving part of their strokes, said linkage each comprising a crank arm pivotally mounted for movement about a first fixed fulcrum intermediate its ends, a sweep arm pivotally mounted at one end for movement about a second fixed fulcrum, said crank arm being connected at one end to the actuator and said sweep arm being connected at its distal end to the picker, and a link connecting the opposite end of the crank arm to the sweep arm intermediate its ends.

21. Apparatus according to claim 1, wherein the distance between the point of attachment of one end of the link to the crank lever and the fulcrum axis of said lever is equal to the distance between the point of attachment of the other end of the link to the sweep lever and the fulcrum axis of such lever.

Description

This invention relates to looms for weaving, and more particularly to improvements in pneumatic picking mechanisms of the class intended to actuate normal picking-sticks and which, therefore, are equally adaptable to looms having multi-cell drop-boxes as to looms having plain shuttle-boxes. The mechanism herein described is particularly applicable to wide and/or heavy looms but is capable of general application.

The principal object of the invention is to provide an improved construction of pneumatically-powered picking mechanism which is economical in its consumption of compressed air, and which, once correctly adjusted, may be relied upon to provide a succession of picking-impulses of substantially equal energy.

A further object is to provide reliable and convenient means for controlling the operational sequence and timing of two such picking mechanisms in due relationship to the loom's crankshaft, or equivalent shaft, so as to afford either alternate or pick-at-will sequence.

According to the present invention a pneumatic picking motion for a weaving loom includes a respective linear-actuator located at or near each end of the loom and supply means adapted to charge the said actuators for successive picking-impulses thereof with a predetermined volume or charge of compressed air at a predetermined pressure, each said actuator being mechanically linked, directly or indirectly, to a respective picking-stick and drive adapted to impart a driven motion thereto on energization.

The picking-stick, by means of a suitable picker, accelerates the shuttle to a discharge velocity necessary to carry it across the width of the loom and into the opposite shuttle-box, within the time allotted for the shuttle's flight, and upon completion of the picking-impulse, the power-piston of the linear actuator being air-cushioned to bring it and its attachments to a halt and then return them to their initial positions, while the compressed air charge is renewed, all in readiness for the next picking-impulse.

The operation of two such actuators, in respect to their operational sequence and timing in synchronism with the loom crankshaft, is controlled by servo-actuated poppet-valves incorporated in each actuator in response to electro-pneumatic controlling means which may provide either alternate or pick-at-will sequence according to the requirements of the loom.

It is desirable in view of the non-uniform force exerted by the pneumatic mechanism to the picking-stick or picker to provide a mechanical-linkage, or comparable variable leverage device, capable of transmitting, and compensating for, the non-uniform force exerted by the pneumatic mechanism to the picking-stick in such manner that the picking-stick, the picker, and the shuttle are subjected to a substantially uniform propelling force, implying a close approximation to their uniform acceleration.

Thus, according to a further feature of the invention, a mechanical-linkage or comparable variable-leverage transmission device is preferably provided between the actuator and the picking-stick, with the effect that, as closely as practicable or desirable, the non-uniform thrust exerted by the piston during its picking-impulse is converted into a uniform force to be transmitted to the picking-stick.

The invention will be further described with reference by way of example only, to the accompanying drawings, of which:

FIG. 1 is a vertical section through the actuator showing its principal components, i.e. the piston and cylinder, the air-container and the valve-box, the latter showing the three poppet-valves as they are disposed during the intervals between picking-impulses;

FIG. 2 is similar to FIG. 1, but showing the poppet-valves as they are disposed to effect a picking-impulse;

FIG. 2a is a view similar to FIG. 2, but showing a modified structure;

FIG. 3 is a side elevation of the actuator shown in FIG. 1 complete with air-container, a valve-box and servo-piston block;

FIG. 4 is a plan corresponding to FIG. 3;

FIG. 5a is a diagram showing rotary-cam controlling means for alternate picking sequence;

FIG. 5b is a diagram showing combined pattern-chain and rotary-cam controlling means for pick-at-will sequence;

FIG. 5c is a diagram showing combined shuttle-box swell and rotary-cam controlling means for pick-at-will sequence;

FIG. 5d is a diagram showing a variation of FIG. 5c;

FIG. 6 shows the actuator coupled to a simple non-compensatory crank-lever;

FIG. 6a is a typical pressure-displacement diagram for the compressed air expanding into the actuator cylinder during the power impulse;

FIG. 6b is a typical diagram for the air under compression and subsequent expansion during the cushioning and reversal of the power-piston and its attachments;

FIG. 7 shows the actuator coupled to a partly compensatory crank-lever;

FIG. 8 shows the actuator coupled to a fully compensatory twin-lever linkage;

FIG. 9 is a graph showing the comparative horizontal pulls at the top of the sweep-lever during the picking-impulse for the three lever systems shown respectively in FIGS. 6, 7 and 8.

Referring to FIGS. 1, 2,3 and 4, each linear-actuator comprises a piston 1 which is an air-tight sliding fit in a cylinder 4. The piston-rod 2 slides through the front cover 5, which is provided in the usual manner with a sealed gland consisting of the bush 5b and the sealing ring 5c. The protruding end of the piston-rod is equipped with the eye-shackle 3.

The cover at the other end of the cylinder takes the form of a valve-box 6, which is tied to the front cover 5 by the through bolts 4c. Mounted on the valve-box, preferably in a vertical position, is an air-container 7 of suitable volume. The valve-box 6 contains three poppet-valves with their appropriate ports or passages.

The first of these poppet-valves is the supply-valve 10, which is provided with a closing spring 10a acting on a color 10b secured to the valve stem. As shown in FIG. 1, this supply-valve is held off its seat by a servo-piston 10c, thereby allowing compressed air from the main supply 8A to flow through pipe-coupling 8, past the open supply-valve 10, and through port 9 into the air-container 7, until it has stabilized at the particular pressure for which the regulator, which is of known pressure-reducing type, is set.

The exhaust-valves 12, when free to open as shown in FIG. 1, affords free communication from the power side of the piston 1, through ports 15 and 13a and outlet 13, to atmosphere. This valve is controlled when necessary by servo-piston 12c.

The pick-valve 14, shown in its closed position in FIG. 1, is provided with a closing spring 14a, and is adapted to be lifted off its seat to its fully open position (shown in FIG. 2) by the servo-piston 14c. When closed as shown in FIG. 1, this pick-valve prevents air from the air-container 7 entering the power cylinder 4 through port 15.

The three servo-pistons 10c, 12c and 14c are a sliding fit in the bores provided in the servo-cylinder block 11, such block being rigidly tied to the valve-box 6 by studs 11a. Compressed air from an auxiliary supply 19A to the servo-pistons is controlled by a slide-valve 19, the slide-valve being retained in a non-energized condition (indicated symbolically in FIG. 1) by a spring 19b. In these circumstances, which exist during the intervals between picking-impulses air is admitted to pressurize the servo-piston 10c which lifts the supply-valve 10 and retains it in its open position as shown in FIG. 1, while at the same time the connection 17, which is common to the servo-pistons 12c and 14c is opened to atmosphere, thereby rendering them inactive.

Referring now to FIG. 2, a picking-impulse may be initiated by closure of the switch 20, by any suitable controlling means such as those later herein described. Such closure energizes the solenoid of the pilot-valve 19c, which, in turn, pressurizes the slide-valve 19 against the force of its return spring 19b, with the resultant effect that the connection 16 to the servo-piston 10c is opened to atmosphere, whereupon the supply-valve 10 closes, while the servo-pistons 12c and 14c are pressurized through connection 17, whereby the exhaust-valve 12 is first closed and held firmly on its seat, and the pick-valve 14 is lifted to its fully open position, in that sequence. The opening of the pick-valve shortly after closure of the exhaust-valve is as a consequence of the air pressure on the servo-piston 14c having to build up sufficiently to overcome the air pressure acting on the head of the pick-valve plus the force exerted by its closing-spring. When the pick-valve is thus raised off its seat, the air pressure on the valve-head becomes partly balanced, and consequently the pick-valve shoots fully open. The servo-pistons 10c and 14c may be cushioned by leather or rubber washers 11c.

Upon the almost instantaneous opening of the pick-valve 14, which places the air-container 7 in direct communication with the power-cylinder 4, the pressure of the air stored in the air-container becomes immediately effective on the power-side of the piston 1 which, therefore, is forcibly displaced at increasing velocity while, as the expansion proceeds, the pressure of the air in the air-container and cylinder reduces in the general manner indicated by FIG. 6a.

In the accompanying drawings, the range of the power-impulse displacement is indicated by P and of the cushioning by C.

At the end of its useful power-stroke, which is about 80 percent of its total stroke, the piston 1 uncovers a circumferential band of holes, or exhaust-ports 4a, in the cylinder wall, through which ports the expanded air, now at diminished pressure, escapes freely to atmosphere. A second band of holes 4b, is provided, spaced apart from the first band 4a by a distance which depends upon the thickness of the piston 1. During the early part of the power-stroke, the air at the back of the piston, escapes freely to atmosphere through both bands of (4(ra and 4b), and later, as the piston covers the first band 4a, through the second band 4b, by which means the back pressure opposing the piston's power-stroke is minimal.

At or about the position in the power-stroke when the piston, then moving at its maximum velocity, has begun to uncover the first or exhaust-band of holes 4a, the piston covers the second band 4b, thereby trapping the air in the cylinder between the piston 1 and the front cover 5. Compression and subsequent expansion of this trapped air, in the manner indicated by FIG. 6b, serves effectively to cushion the piston and its attachments and, after bringing them quickly and silently to a halt, to start them on their return stroke which is completed under the force exerted by a return-spring (not shown) in the manner indicated at S in FIGS. 6, 7 and 8. This spring is equivalent or additional to the return-spring usually provided to return the picking-stick and picker to their initial positions.

Towards the end of, or quickly after, the completion of the picking-impulse, which occurs in a fraction of a second, the switch 20 of FIG. 2 (or its equivalent later described herein) is opened. This de-energizes the solenoid of the controlling slide-valve 19, which promptly reverts to its spring-controlled position (indicated in FIG. 1) with the resultant effect that in rapid succession, the pick-valve 14, closes under the force of its closing-spring, the exhaust-valve 12 opens, and finally, the supply-valve 10 opens to renew the charge of compressed air in the discharged air-container 7.

The opening of the exhaust-valve 12, which is held firmly on its seat during the picking-impulse, enables the returning piston to expel the air that would otherwise be trapped after the piston had returned sufficiently to cover the exhaust-ports 4a. As the piston completes its leisurely return-stroke, air from the atmosphere freely enters both bands of holes (4a and 4b) in the cylinder wall then behind the piston.

In order to initiate a picking-impulse at either end of the loom, it is merely necessary to energize the solenoid of the slide-valve controlling the actuator at the appropriate end of the loom at the correct moment in the loom cycle.

Referring to FIG. 5a, in the case of a loom having plain shuttle-boxes and calling, therefore, for alternate picking sequence, i.e., first from one end and then from the other, the selection and timing are preferably effected by a timing-cam 22 rotating at half crankshaft speed and arranged to actuate, at 180 degree intervals, two micro-switches 23a and 23b, thereby serving to energize in turn the solenoids of the controlling slide-valves 24a and 24b, by which means the two actuators are caused to function in the desired alternate sequence, and also at the correct moment in the loom cycle. The hand-switch 21 (common to FIGS. 5a, 5b, 5c and 5d) may be opened to suspend the operation of the picking mechanisms when so desired.

Referring to FIG. 5b in the case of a loom having multi-cell drop-boxes and calling, therefore, for pick-at-will sequence, the order of picking may be indicated by an extra line of bowls and tubes added to the usual box-motion pattern-chain. The selection as to which actuator shall next function is then dependent upon the indication of chain 25, but the actual timing of the pick is controlled by the timing-cam 28, rotating at loom crankshaft speed, which closes the micro-switch 28a to complete the circuit of the controlling slide-valve 24a or 24b, as selected by the chain 25. By means of finger-lever 25a the chain actuates a double-pole micro-switch 26 (which is provided with return-spring 26a) to the effect that a bowl on the chain selects the solenoid of slide-valve 24b, and a tube selects the solenoid of slide-valve 24a.

Referring to FIG. 5c, which shows controlling means applicable to either alternate or pick-at-will sequence, the picking order is selected automatically by the interaction of two single-pole micro-switches 32a and 32b, which are respectively actuated by the aligned shuttle-box swells 31a and 31b, to the effect that the pick next occurs at that end opposite to which an empty box has last been aligned with the shuttle-race by the normal operation of the box-motion (not shown) in readiness to receive the picked shuttle. As shown in FIG. 5c, the shuttle-box 29a is empty and ready to receive a shuttle discharged from the opposite box 29b. In these circumstances, the swell-switch 32a being closed, the solenoid of the slide-valve 24b is energized thereby causing the shuttle 30 to be discharged towards the empty box 29a while the solenoid of the slide-valve 24a remains inactive because of the open swell-switch 32b. The timing-cam 28 and switch 28a function as described with reference to FIG. 5b.

It will be apparent, considering the controlling means shown by FIG. 5c, that if, by chance, both the aligned boxes contain shuttles, neither actuator will function. On the other hand, if both the aligned boxes are empty, both actuators will function. In order to turn the loom over for pick-finding purposes, the hand-switch 21 may be opened to put both actuators out of action during such temporary operation.

In a modification of FIG. 5c shown in FIG. 5d the two swell-switches 33a and 33b are of the double-pole type which interact to the effect that, as with FIG. 5c the pick next occurs at that end opposite to which an empty box has last been aligned by the normal action of the box-motion, but, in addition, that neither actuator will function in the event of both the aligned boxes being (i) empty, or (ii) full. The timing-cam 28 and timing-switch 28a function as described with reference to FIG. 5b, while both actuators may be temporarily put out of action by the operator opening the hand-switch 21.

Referring to FIGS. 5a, 5b, 5c and 5d, the timing-cams may be designed to hold their timing-switches closed for a period of time about 50 percent longer than that occupied by the picking-impulses, so that the energized slide-valve is allowed quickly to revert to its spring-controlled position, and, therefore, the piston 1 and its attachments to commence their return-stroke with minimum delay. Alternatively, additional switches, shown at 27a and 27b, may be included in the circuits of the slide-valves 24a and 24b. These switches are normally closed, but are opened by the action of each energized actuator as or shortly before it completes its picking-impulse. This feature will be further described later herein with reference to FIG. 8.

Referring to FIGS. 3 and 4, the actuator is provided, in the usual manner, with trunnions 6t, 6t which are adapted to rock freely in bearings formed in or mounted on the loom structure, whereby the axis of the cylinder may swing in response to the movement of the eye-shackle 3 along a curved path.

Referring to FIG. 6, in which the actuator-cylinder 4 and piston 1 are indicated in outline, the eye-shackle 3 on the piston-rod 2 is coupled by pin 34 to the crank-lever 35, which has its fulcrum at 37. The pin 34 thus follows a curved path, and the actuator, as a complete unit, swings accordingly on its trunnions 6t, 6t.

The sweep-lever 36 is either formed in one piece with the crank-lever 35, or separately, in which case the crank-lever and the sweep-lever are individually clamped on or keyed to a rocker-shaft corresponding to the fulcrum 37.

The sweep-lever 36 has a pin 38, at its maximum radius, to which pin the inner end of the lug-strap, or lug-stick 39, is attached, while the outer end of such lug-strap or lug-stick is coupled in the usual manner to the picking-stick (not shown). In its ready-to-pick position, shown by FIG. 6, the sweep-lever 36 rests against an adjustable stop 41, and is retained in that position by a light return-spring S coupled to pin 40, or attached to the levers in any other convenient manner.

FIG. 6a is a typical diagram showing the air pressure acting on the piston 1 after the opening of the pick-valve 14. (See FIG. 2) in this example, the pressure commences at 75 psig and falls to about 20 psig as the air expands behind the accelerating position, until this uncovers the exhaust-ports 4a to allow the spent air to escape to atmosphere. In this example, the mean effective pressure acting on the piston is 40 psig.

Due to crank-lever 35 and the sweep-lever 36 being in diametrically-opposite alignment and, furthermore, the axis of the actuator-cylinder being approximately at right angles to the above levers when they are midway in their angular sweep, the non-uniform thrust of the piston is transmitted without sensible modification of compensation to the crank-lever 35, and thence to the sweep-lever 36, so that the lug-strap 39 is subjected to a widely ranging horizontal pull, commencing at 100 percent and finishing at about 27 percent, or by ratio 3.75 to 1.

Whilst the actuators as herein described may be utilized to actuate the picking-sticks of a weaving loom through the media of non-compensatory transmission-linkages such as that shown in FIG. 6, it is eminently desirable that the accelerating force exerted on the picking-stick, the picker, and the shuttle, shall be as nearly uniform as possible throughout the picking-impulse.

Referring to FIG. 7, in which the item references correspond to those of FIG. 6, the crank-lever 35 is set out of direct alignment with the sweep-lever 36, whereby the effective radius of the crank-lever 35 is R at the commencement of the impulse but increases to about 2.27R at the end of the angular sweep marked P. In all other respects, the arrangement corresponds to that shown by FIG. 6.

The useful effect of the automatic and progressive increase of the effective radius of the crank-lever 35 during its angular sweep P (which corresponds to the impulse stroke P of the piston 1) is to narrow the range of pull to be transmitted by the lug-strap 39. This pull now commences at 59 percent, increases to 62 percent, and finishes at about 40 percent, or by ratio 1.55 to 1, which is a marked improvement over the arrangement of FIG. 6. The simple variable-leverage device shown in FIG. 7 thus affords a very fair measure of compensation, and is a useful compromise for certain applications of the invention.

Referring to FIG. 8, which shows a twin-lever transmission-linkage which provides practically ideal compensation, the eye-shackle 3 on the piston-rod 2 is coupled by pin 34 to the top of the crank-lever 35, which has its fulcrum at 43. The lower arm 44 which, in the form shown by FIG. 8, is in direct alignment with the upper arm or crank-lever 35, is coupled to the sweep-lever 36 by the link 46. The radius of the pin 45 from its fulcrum 43 is preferably made equal to the radius of the pin 40 from its fulcrum 37. The two fulcrums 37 and 43 and the actuator-trunnions 6t, are rigidly supported in or on the loom structure (not shown).

The essential feature of this transmission-linkage is that whereas at the beginning of the angular sweep P, the effective radius of pin 45 is 2R while that of pin 40 is R, at the end of the sweep, the effective radius of pin 45 has reduced to R while that of pin 40 has increased to 2R, thereby providing an automatic four-fold increase of leverage during the angular sweep. The corresponding centre-distance between the fulcrum 37 and 43 is 6R. The graphs of FIG. 9 give a useful comparison of the degree of compensation afforded by the lever-systems shown in FIGS. 6, 7 and 8. Curve 6 relates to the non-compensatory lever-system of FIG. 6, and shows that the lug-strap pull varies in direct ratio to the wide range of air pressure acting on the actuator-piston. Curve 7 relates to the simple, although partly compensatory, lever-system shown in FIG. 7, and indicates a very fair degree of compensation. Lastly, curve 8 relates to the twin-lever system shown in FIG. 8, for which the ratio of maximum/minimum pull on the lug-strap is only 1.085, implying an exceptionally close approximation to uniform acceleration of the lug-strap, the picking-stick, the picker and the shuttle.

Referring to FIGS. 5 and 8, the additional switches 27a and 27b (previously referred to) are preferably actuated as shown in FIG. 8. A micro-switch 27, which is normally spring-closed, is mounted on the loom structure and adapted to be opened by the oscillatory cam 50 as, or shortly before, the levers complete the impulse swing P. The energized slide-valve is thereby allowed to return, with minimal delay, to its spring-controlled position, and, therefore, the piston and its attachments promptly to commence their return-stroke. When these switches 27a and 27b are employed with the above effect, the angular spread of the lobes on the timing-cams 22 and 28 is not so critical as when the cams are required to interrupt the circuit of the energized slide-valve at the appropriate point in the piston's power-stroke.

The energy released during the picking-impulse depends upon the physical volume of the air-container 7, and the pressure of the air stored therein in readiness for the next pick. It has been found by practical experiment that a convenient ratio of expansion is about 2 which implies that the volume of the air-container shall be about equal to the displacement-volume of the piston during its power-stroke, i.e., neglecting the cushioning or overrun part of the piston's total stroke.

The compressed air is preferably supplied directly from a compressor, so as to conserve as much of the heat of compression as possible. Alternatively, or additionally, the compressed air may be pre-heated just prior to its entry into the air-container 7, or after is entry therein. Electric heating is convenient for this purpose, and an electric heater 7h may be fitted in the air-container 7, as indicated by the dotted lines in FIG. 1.

Pre-heating is beneficial in reducing the consumption of compressed air, since the air-container of fixed volume holds a smaller weight of heated air as compared with air at the same pressure but at room temperature. A considerable proportion of the heat either retained in or added to the compressed air is converted into work in the actuator-cylinder. Pre-heating also avoids the unduly low exhaust temperatures that would otherwise result from the expansion, with the danger of ice formation and a local atmospheric cooling effect.

It is noteworthy that, for the present purpose, the air-compressor is merely required to compress the charge of air up to the specified pressure, but not to deliver it at that, or a higher, pressure. Similarly, the charge of air stored in the air-container at the specified pressure, merely expands into the actuator-cylinder; there is no admission period prior to cut-off, as a preliminary to the expansion period, as in the normal theoretical diagram for a steam-engine. It follows that the power required to drive a compressor for the present purpose is only about one-third that required when the compressor is working on full-load duty, i.e., compressing air up to and delivering it all at the specified or even higher pressure.

Referring to FIG. 6, 7 and 8, in some applications of the invention it is preferred to mechanize the adjustable stop 41 against which the sweep-lever rests under the light pull of the return-spring S. The stop 41 is covered with leather or rubber to cushion and silence the small impact of the lever 36 against the stop. The actual position of the stop may be controlled, by a cam rotating at loom crankshaft speed, to the effect that the spring S, or its equivalent, is allowed to increase the angular sweep of lever 36 and thereby withdraw the pickers from contact with the shuttles while the drop-boxes change their positions. Upon completion of the change, the cam restores the lever 36 to its normal ready-to-pick position, and restores the picker into contact with the newly aligned shuttle.

In the modification illustrated in FIG. 2a, the poppet-valve 10 is dispensed with, and the connection 16 from the slide-valve is arranged to supply the charge of compressed air to the air-container 7. A check-valve 9c is interposed in the connection 16 to prevent air from the air-container discharging back through the slide-valve when this is energized to initiate the picking-impulse as shown by FIG. 2.

It is to be appreciated that the controls as illustrated in FIGS. 5a to 5d may well be of application in other contexts, and indeed the electric coils incorporated in the slide-valves 24a and 24b can be considered simply as coils for the magnetic energization of any switch device, such as a fluid-pressure valve, or an electro-magnetic clutch or brake, by which stored energy, of any form, may be triggered-off and released to do work.

The compensatory-lever arrangements shown in FIGS. 7 and 8 are also of possible application in contexts other than that hereinbefore disclosed, and indeed such arrangements are thought to be of use in connection with either fluid-pressure or spring-impulse devices where a sensibly constant acceleration is desired.

The invention is not confined to the particular form or forms illustrated in the accompanying drawings, for instance, the actuators may be mounted with their axes vertical or more vertical than horizontal, and the angular disposition of the transmission-levers modified to suit.

* * * * *

Current U.S. Class:	139/142
Current International Class:	D03D 49/00 (20060101); D03D 49/34 (20060101); D03d 049/34 ()
Field of Search:	60/57 139/144,142