GB2037822A - Automatic Positioning of Machine Elements - Google Patents

Abstract

An automatic position control arrangement for a machine element supported for movement to and fro to a range of positions including two selector members (LS, US) settable by lengthwise movement connected by a swing link (SL) with an output member (PR) slidably connected to the swing link, and operable by the controlled action of each selector held set (SUL, SLL) in turn to act via the swing link on the output member brought to one end (PBU, PBL) of the swing link to positively move a connected (CR) machine element to and fro to a desired position in the range of positions, allowing the other selector to be reset without affecting the output member position. The selector members may be controlled by a single electric stepper motor (AC) and a rack and pinion linkage (PR) to a further swing link (BL) pivotally coupling the selector members. The machine element may be a pattern guide bar of an automatic warp knitting machine, such as a Raschel machine, and the selector action may be controlled, together with other selectors for other bars, from a store of pattern instructions and appropriate reading means responsive to the store contents to control the selectors and thereby the bars positively without the aid of a return spring in accordance with the stored pattern instructions and in time with the machine drive. Conveniently the store is part of an electronic computer arrangement also including store input means and having store access and examination means such as a keyboard and VDU whereby pattern changes can be made during knitting. <IMAGE>

Description

SPECIFICATION Automatic Positioning of Machine Elements This invention relates to the precise, positive and automatic positioning of machine elements movable from one position to another in operation of a machine.

When machine elements are required to be moved into a selected position for operation the operating position can often be selected accurately by a fixed stop member such as an abutment or set-screw. However in some cases the required position cannot be selected in this way. Automatic machinery in particular can require quick and precise positioning and repositioning of machine elements in a number of positions without a large penalty in cost and complexity and preferably in response to numerical control signals.

For example in some types of knitting machine a warp guide bar extends alongside a bank of needles and carries a number of warp yarn guides to co-operate with the needles. The guide bar has to be moved lengthwise in a controlled manner to a sequence of different positions during knitting.

Clearly the movement must be controlled so that the yarn guides can co-operate correctly with the needles in each position into which it is moved.

That is the needles and guides must be able to mesh in the same relation in each position. In view of the damage and consequent cost of any error in position control the control must be precise and reliable. To achieve worthwile production rates the control must be quick in its action and the repositioning accuracy must be of a high order.

For many years such control has been achieved by mechanical means. Briefly a guide bar has an associated linkage such as a push rod connected buy a lever to a thrust pad engaged by a cam precisely ground to a profile known to give the required position control sequence as the cam moves past and drives the thrust member. To remove slack in the linkage and return the guide bar a very strong spring is used. To provide a long sequence of positions the control cam is actually a pin-and-link chain each link providing a cam element shaped by precision grinding.

This type of control is exemplified by the Raschel warp knitting machines. In these machines several guide bars are provided. The bars are mounted side-by-side in an arc and are movable towards the centre of the arc together to co-operate with the needle bank. Lengthwise movement by the above-described cam action occurs before the bars are moved towards the needle bank.

When a complicated pattern is to be knitted there may be some thirty-six, or more, guide bars each movable over a considerable distance, usually expressed in needle spacing or "gait". The bar movement has two components, a patterning movement selected by the individual cam action and a programme movement which is the overall movement of cumulative patterning movements.

The terms patterning and programme movement are used here in these senses. Typical chaincontrolled machines have patterning movements of some 1 3 gaits or needle spaces and programme movements of up to 48 gaits. A normal practical limit to chain length is 650 selections, i.e. links. Clearly each patterning movement when controlled by a chain cam is limited by the time interval available to move the guide bar without risk of damage and the practical cam height and thrust load for tolerable wear. A typical needle pitch is 1 8 to the inch (about 8 per cm) which requires an accuracy sufficient to reliably position and reposition a guide bar into individual operating positions spaced at about 0.055 inch (0.13 cm).

The size of the machine and speed of operation against the heavy return spring load requires a massive guide bar control unit including a chain with a strand for each bar. The massive size reduces the speed of response to the control. As the chain has to be specially made for each pattern to be knitted the capital cost in material and labour is very high and any change to the pattern requires alteration of the chain. There is also the high expense of maintaining chains and the capital involved in storing chains for further use. This problem and an improved chain are discussed in UKPS 1130211. However chains, while durable and reliable when installed, remain cumbersome and costly.

Attempts have been made to replace the chain with a control arrangement based on a punched paper tape regulating the action of hydraulic or pneumatic actuators operable to move the guide bars in the same manner as the chain link cams, in accordance with the punchings in the tape and to bring about knitting of a pattern represented by these punchings. Such arrangements are exemplified by UKPS 888701, 1241638 and 1352857.

A difficulty experienced in practice with hydraulic or pneumatic controls (i.e. fluid pressure controls) arises when precise movement to several positions is required. As mentioned above movement into and out of a single position is relatively simple but accurately controlled movement of a heavy load such as a guide bar to any one of several repeatable positions in short time intervals is much more difficult particularly when it has to be achieved by the operation of a fluid pressure actuator.

Techniques based on accumulating in one actuator metered components thrusts from subsidiary actuators have been proposed but the fluid pressure system required is complex and has to be of high precision. This causes high initial costs and requires skilful maintenance, so that these costs can outweigh the savings on chain manufacture. The noise level of fluid pressure devices for such high speed duty is likely to be high while the reliable life is likely to be only a few months. Thus the control mechanism is likely to fail more often than the machine.

USPS 3802227 shows a cam-operated link system using eiectromagnets singly or in selected combinations to increase the effect of the cam.

There is therefore a need for an economic technique for the precise positive positioning of machine elements which does not suffer from the problems of power requirement and size resulting from positioning "on load".

It is an object of the invention to provide an arrangement to give precise positive position control of machine elements in a flexible and economic manner.

According to the invention there is provided a machine element automatic position control arrangement for a machine element supported for driven movement to and fro to a range of selected positions including a pivotted arrangement of two selector members connected by a swing link and settable by lengthwise movement and an output member to transfer movement of the swing link to the machine eiement, the swing link providing output member pivot points at each selector connection and the output member being slidably connected for driven movement along the swing link, the arrangement also including locking means effective to lock the selectors during movement of the output member from one pivot point to another, driving any connected element.

Preferably the setting of a selector member is controlled by a transducer such as an electromechanical device having a set polarised incremental movement in response to a sufficient electrical input of appropriate polarity. In a particular use of the invention a selector member setting means includes a single electric stepper motor, a rack and pinion and a further swing link pivotally coupling the selector members.

Each selector locking means may be effective to hold the set selector and the respective pivot point of the swing link locked for displacement action on the output member driven along the swing link. The locking means may release a selector for movement by a selector setting means to a selected position without moving the output member while the other selector remains locked in selected position defining the output member setting. The locking means may be a rack device.

In one application of the invention the machine element is one of the pattern guide bars of an automatic warp knitting machine, such as Raschel machine, and the selector action is controllable from a store of pattern instructions and appropriate reading means responsive to the store contents to direct the operation of at least one stepper motor to control the selectors to position the bar, and via other selectors other bars, positively without the aid of a return spring in accordance with the stored pattern instructions and in time with the machine drive.

Conveniently the store is part of an electronic arrangement also including store input means such as the tape reader and having store modification access and examination means such as a keyboard and VDU. Some or all of the bars of the knitting machine may be controlled in this way.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a position control arrangement for a machine element in the form of one pattern guide bar of a Raschel warp knitting machine; Figure 2 shows in outline another position control arrangement.

Referring first to Figure 1 this shows a side elevational view of one pattern guide bar control arrangement for a Raschel machine. In practice several such arrangements are provided, usually one for each guide bar, but for clarity only one is shown and discussed. The application of the arrangement for several guide bars will be readily apparent.

The arrangement shown is connected to a machine guide bar by a connecting rod CR which extends in the same general direction as the guide bar (not shown). Transversely of this direction there is a selector guide frame, SGF, formed of a number of connected parallel members spaced apart to provide a rigid support. Frame SGF can be formed in any convenient manner, e.g. from spacers assembled on tie rods or rectangular bars slotted at intervals to provide grooves such as GS in which upper and lower selective members US, LS respectively are able to move freely in a lengthwise direction (arrows SSU, SSL) while constrained against deflection or movement in other directions. Grooves GS can be provided with anti-friction or hardened surfaces such as SS to ease the sliding of the selector members and reduce wear.The frame SGF thus securely and stably defines the motion of the selectors US, UL.

Each selector has a pivot support arm, PAL for selector LS and PAU for selector US.

As shown in scrap section Figures 1 a each pivot arm is formed by two plates defining an aperture into which a pivot bush (PBL, PBU) of nylon or like low friction durable material closely fits and is held by its shape when rotated to the position shown in Figure 1 a. Each pivot bush, PBL, PBU, is free to turn in the pivot arm but is kept in position by a swing link SL which links the selectors LS, US by engaging the bushes PBU, PBL in position in the pivot arms; Swing link SL is formed by two link bars, LB 1, LB2 held in closefitting relation to the bushes PBU, PBL by a bolt UCB and a clamp tube LCT at their upper and lower ends respectively.

Each selector has attached to it an associated rack SLLR and SULR, which can be engaged by a - locking rack operated via respective lugs SLL and SUL (arrow L). When the locking rack engages the rack attached to the selector, the selector is held in position against lengthwise movement, for example the reaction from the load on the output member CR.

To summarize the selectors US, LS are pivotally linked by swing link SL at pivot bushes PBL, PBU and can be locked in a selected lengthwise position by a rack SULR and SLLR.

A push rod PR of two parallel elements is supported in the same plane as selectors US, LS by change bar guides CBG. Push rod PR carries between the elements a coupling SLC, in the form of a roller bearing, which engages between link bars LB1, LB2 (see Figure 1 a). Change bar guides CBG are shaped to support push rod PR against deflection while permitting longitudinal movement. The change bar guides CBG are themselves supported for driven movement in the plane of the Figure, as shown by the arrows C, to reciprocate push rod PR from one to another of pivot blocks PBL and PBU so that coupling SLC can engage the respective pivot in turn. The outer end of push rod PR acts on an outer guide link OGL through a roller bearing coupling OGC.Link OGL is fixed to connecting rod CR and supported in the structure CRG, which includes frame SGF, for movement in the sense of arrow OP in a manner not shown. Link OGL is generally similar in form to swing link SL and is not described further. Connecting rod CR slides in guide CRG. In this way lengthwise control motions of push rod PR are transmitted to connecting rod CR as push rod PR is moved by guides CBG alongside link SL.

All the various motions are co-ordinated with the action of the machine by suitable mechanical or other means.

To further summarise, by the combined action of the change bar guides and selectors the outer guide link can be moved to and fro in a controlled manner. Thus consider selector LS locked by rack SLLR in the location shown and push rod PR moved by change bars CBG to bring coupling SLC into pivot bush PBL. If selector US is now moved, in the sense of arrow SSU, to move pivot bush PBU away from connecting rod guide CRG then swing link SL will turn on the pivot bushes without moving push rod PR. If selector US is now locked in the new location by rack SULR and the change bar guides driven to move push rod PR towards selector US the coupling SLC is displaced along the now inclined swing link SL.This displacement of coupling SLC displaces push rod PR lengthwise in the sense of arrow 0 and, via coupling OGC and link OGL, pulls connecting rod CR through guide CRG in the sense of arrow OP to a fresh position.

This action permits connecting rod CR to be held in place to maintain a connected guide bar in an operating position during an operating cycle of the knitting machine. Meanwhile the selector LS is moved to and locked in a next required location for a fresh position for connecting rod CR, i.e. in the next cycle, which fresh position is then quickly applied by the movement of change bar CBG when required. A further fresh position is then provided by unlocking and moving selector US and locking it in a suitable location while connecting rod CR is still held in position by locked selector LS. Selector movement can thus take place during the relatively long period (several tens of milliseconds) when a course is being knitted, even at a machine rate of 400 courses per minute.

The manner in which the selector locations are achieved will now be described. The selectors LS, US are coupled by a further link, back link BL. This link is pivotted to the upper selector US at pivot BLP. At the lower selector LS a fork and pin coupling BLY is provided. This fork coupling allows for the increase in length needed in link BL when the selectors are displaced past one another. A rack and pinion drive system is supported adjacent to link BL to couple with it at coupling BLC. The drive system includes upper and lower rack guides RGU, RGL extending between a rack guide support RGS and an actuator support ACS. Support ACS carries an actuator of a control-signal to displacement transducer. In this embodiment the transducer is a stepper motor AC having a drive pinion P to drive rack R in accordance with the energisation of the stepper motor.Rack R is mounted between guides RGU, RGL and connected to rack follower RF which in turn is secured to back link BL, by coupling BLC. Coupling BLC is housed in a slot in link BL to permit movement as the link inclines from the vertical with relative movement of the selectors.

The operation of the selector drive is as follows. When one selector, say US, is locked in a location the operation of motor AC will move rack R and thereby cause link BL to pivot on pivot BLP.

Through fork-andpin coupling BLY the lower selector LS is also moved and with appropriate operation of motor AC will reach a fresh required location, at which it can be locked to control the position of connecting rod CR in due course as described above.

An important advantage of the arrangement described herein will now be considered. In the operating cycle of a Raschel machine each pattern guide bar is required to move to and fro by varing amounts from position to position as the pattern progresses. The arrangement described herein when applied to individual bars has the advantage that when the bar has been put in one position the next position can be set up during the dwell period until the bar is again required to move at which point the bar is quickly put into the new position by the action of the change bar guides. This means that the drive for the selectors never has to actually move the bar and can thus be of low power. Also the drive for a selector does not have to hold it in position against load reaction. Furthermore the positive connection of the arrangement means that a return spring, used hitherto, is not required.

The load on the selectors is thus reduced in comparison to that for chain setting and wear and noise also reduced, while retaining setting accuracy and even improving it.

In this way a larger patterning movement can be achieved in the time allowed. The time at which the movement is to occur is easily derived from the mechanism of the knitting machine and applied by a mechanical linkage to change bar guides CBG. With suitable supports to keep the various elements stiff it is also possible to increase the total excursion of program movement. Typically a patterning movement of some 17 gaits or needle spaces and a programme movement of some 90 gaits would be possible at normal production knitting speeds now in use. As the control chain is no longer needed a pattern involving up to say 2600 steps at least would be practical, using say a punched paper tape control medium or information stored in a computer memory.

The precision of the control is determined in part by the stepper motor. The rack and pinion linkage ensure that the same amount of movement is applied at each step in the setting of the back link BL so the selectors are precisely and reliably set without the need for adjustment. Wear is unlikely to affect the setting accuracy as could happen rapidly with hydraulic or pneumatic actuators under the pattern bar load and the uncertainty of the cumulative action of several actuators is removed.

Further precision can be provided by the racks SLLR and SLUR. These can be provided with Vnotch teeth pitched at the needle spacing and thus ensure that only positions in which the needles and yarn guides should be set are used. In this way an error will only spoil a piece being knitted and will not risk damage to the machine by clashing of needles and guides. A similar locking rack can be introduced on the machine pattern bar if required as a further check against incorrect setting due to wear in the selector arrangement. If required additional protection against failure can be provided by using an easily breakable part in the outer link OGL or by including an electrical warning device actuated by overload in the output member.

While hydraulic and pneumatic devices can prove unsatisfactory as a direct replacement for the chain link cams operating a pattern bar directly such transducer devices, or other transducers such as linear electromagnetic devices, could be satisfactory when operating the very smali load of the selectors described above.

Accordingly while stepper motors are very convenient electromechanical transducers for selector drive, other transducers such as fluid pressure ones are not excluded from use in the embodiments of the invention.

Conveniently the stepper motor AC executes up to ten steps, say between three and seven, to move a selector the equivalent of one needle pitch or gait. Clearly more or iess steps, including half steps, may be used. The motor operation can be controlled in any suitable manner. One convenient manner is to use an electronic circuit arrangement, such as a computer, having a store into which the stepper motor instructions can be placed. In practice in a Raschel machine a position control arrangement as illustrated will be provided for each pattern bar say, thirty six or more, with one stepper motor on possibly two, see Figure 2, for each bar.The stepper motor instructions for a particular pattern of knitting, analogous to the cam sizes on the chain used hitherto, can be produced on magnetic tape, punched paper tape, punched card or other suitable storage media and read into the store.

The instructions in the store can be altered if required and a permanent record on tape etc., prepared for future use, e.g. if a variant in the original pattern is required. The cost of preparing a pattern, altering a prepared pattern, changing from one pattern to another and storing patterns for re-use are all greatly reduced both in terms of money and space.

The stepper motor instructions for all the bars involved are read out from the store in synchronism with the mechanical operation of the Raschel machine to be controlled, in any suitable manner, and the pattern bars thereby positioned to knit the required pattern. The operations will thus be synchronised at all machine speeds from low speed startup to full-speed, the setting arrangement always having ample time to operate in the dwell periods even at full speed but not operating too quickly at low speed as may occur with a fluid-pressure device working directly on the pattern bars and arranged to operate correctly in the high-speed mode.

The speed and ease with which a pattern can be set up and altered permits the trying out and sample production of new patterns with much less expense of time and labour in making chains etc., while minor changes are quickly made, even while the pattern is being knitted if suitable checks are built into the computer associated with the store to prevent mal-operation.

Conveniently a keyboard and VDU can be associated with the store to permit changes. The use and design of suitable stores, VDU's and keyboards is now well known in the electronic control art and no further description will be given. Suitable arrangements can readily be constructed by one skilled in the art from proprietary components or even purchased ready built from a specialist supplier.

The greater range of lengthwise pattern bar movements (as defined above) available as a result of carrying out selector setting movements during a "dwell" period permits a greater range of pattern width and form than hitherto without reduction of machine speed to any significant extent, if at all. Pattern length can also be increased as the weight and size of the chain is no longer a limitation.

Instead of engaging the outer guide link OGL, coupling OGC can be a universal joint to a rod itself universally jointed to connecting rod CR and achieve the same action.

Figure 2 shows in outline another arrangement embodying the invention. In Figure 2 two selector rods 21, 22 are driven by means now shown for example individual stepper motors or other actuators which need not be electric) to control a swing link 23. A push rod 24 is connected Co link 23 by a slipper and is movable by change bar 25 to transfer the movement of link 23 to output shaft 26. In this way the positions 1 to 7 exemplified for link 23 can be produced on output shaft 26. The locks 27, 28 ensure that the selector drive does not have to oppose any reaction from a load on the output shaft 26.

In the arrangement shown in Figure 2 only seven setting positions are shown, by way of example. It will be understood that with suitable sizing and support of the elements a much larger range of setting positions is practicable.

While the invention has been specifically described in terms of an application to a Raschel knitting machine clearly other automatic machine applications are possible. The arrangement described is capable of accurate operation over a long period of use when operated many times a second as is the case in modern high speed knitting machinery. In this precision of movement applied to the pattern bar is maintained. If required the arrangement can be immersed in a suitable closed bath of lubricating oil to further improve the reliable life. Clearly the control arrangements can also be operated at lower speeds with equal usefulness.

The moving masses of the arrangement described above are already smaller than in existing machines and of lower inertia but further reductions can be made, subject to safe working loads, by cutting holes in the movable parts or making them from suitable plastics materials as extrusions, dough-mouldings or other forms. By the separation of the setting and drive loads highspeed low-power setting without the burden of reflected drive loads is achieved. In this way the disadvantages of existing techniques of complexity, noise, short life, unreliability and cost are mitigated by providing a more reliable and simpler mechanism than hitherto available.

Instead of a textile machine using a multiplicity of control arrangements, individual such arrangements could be used in a wide variety of applications such as industrial robots and the precise positioning of heavy loads. Here again, the separation of setting and driving operations would improve accuracy and reduce wear and cost.

Claims (8)

Claims

1. A machine element automatic position control arrangement for a machine element supported for driven movement to and fro to a range of selected positions including a pivotted arrangement of two selector members connected by a swing link and settable by lengthwise movement and an output member to transfer movement of the swing link to the machine element, the swing link providing output member pivot points at each selector connection and the output member being slidably connected for driven movement along the swing link, the arrangement also including locking means effective to lock the selectors during movement of the output member from one pivot point to another, driving any connected element.

2. An arrangement according to Claim 1 in which the setting of a selector member is controlled by a transducer in response to a signal indicating a desired selector movement.

3. An arrangement according to Claim 1 or Claim 2 in which the setting of a selector member is controlled by an electromechanical transducer setting means having a set polarised incremental movement in response to a sufficient electrical input of appropriate polarity.

4. An arrangement according to Claim 2 or Claim 3 in which a selector member setting means includes a single electric stepper motor, a rack and pinion and a further swing link pivotally coupling the selector members.

5. An arrangement according to any preceding claim in which the selector locking means is effective to hold the set selector and the respective pivot point of the swing link locked for displacement action on the output member driven along the swing link.

6. An arrangement according to Claim 5 in which the locking means is arranged to release a selector for movement by a selector setting means to a selected position without moving the output members while the other selector remains locked in a selected position defining the output member setting.

7. An arrangement according to any one of the preceding claims in which the locking means is a rack device.

8. An arrangement according to Claim 7 in which the locking means is arranged to release a selector for movement by a selector setting means to a selected position without moving the output members while the other selector remains locked in a selected position defining the output member setting.

1 5. A pattern bar guide according to Claim 10 or any claim dependent thereon in which pattern bar control is effected by positive drive in both to and fro directions whereby a return spring for the pattern bar is avoided.

8. A pattern bar guide of an automatic warp knitting machine including at least one arrangement according to any one of the preceding claims connected to control a respective pattern bar machine element.

9. A pattern bar guide according to Claim 8 in which the selector action is controllable from a store of pattern instructions and appropriate reading means responsive to the store contents to direct the operation of at least one transducer to control the selectors positively without the aid of a return spring in accordance with the stored pattern instructions and in time with the machine drive.

10. A pattern bar guide according to Claim 8 or Claim 9 in which the store is part of an electronic arrangement also including store input means such as a tape reader and having store modification access and examination means such as a keyboard and VDU.

11. A pattern bar guide according to Claim 9 in which the transducer is a stepper motor.

12. A pattern bar guide according to Claim 8, or any claim dependent thereon in which the selector action is controlled to set one selector while the other is held locked to hold the connected pattern bar in a "dwell" position of the knitting machine cycle.

13. A machine element automatic control arrangement substantially as herein described with reference to the accompanying drawings.

New Claims or Amendments to Claims Filed on 27th March 1980 Superseded Claims 5, 6 New or Amended Claims:

5. An arrangement according to Claim 1 or Claim 2 or Claim 3 or Claim 4 in which the swing link and the output member are slidably connected for positive transmission of movement of the swing link in both to and fro directions of the machine element.

6. An arrangement according to Claim 5 in which the connection between the swing link and the output member includes a bearing movable between close-fitting guides set lengthwise of the link.

7. An arrangement according to any preceding claim in which the selector locking means is effective to hold the set selector and the respective pivot point of the swing link locked for displacement action on the output member driven along the swing link.