GB2174018A - Liquid dispensing apparatus - Google Patents

Abstract

The invention relates to a liquid dispensing apparatus of the type which may be used in the paper production industry for washing the felts which are used to remove water from the paper "pulp" during paper production. The present arrangement comprises a liquid dispensing member which is driven in a reciprocating fashion by a fast reversing electronically controlled stepper motor. The rotational motion of the stepper motor is translated into linear motion preferably by a ball screw arrangement. The fast reversal of the stepper motor means that liquid is not directed at any one area for an over long length of time, and that the felt is therefore washed evenly. The rate of reversal of the stepper motor is variable, and a motion detector is provided to control various functions of the apparatus. <IMAGE>

Description

SPECIFICATION Liquid dispensing apparatus The present invention relates to a liquid dispensing apparatus and more particularly to a liquid dispensing apparatus for use in paper production machines to clean the felts.

In any processforthe production of paper it is necessary at some stage to remove water contained in the "pulp" by suction, capillary action, pressure or gravity, and felts are generally used to help support the pulp and helpfacilitatewater removal during this process. Dirttends to be removed from the pulp with the water, and it is therefore necessary to periodically wash the felts before they can be utilised again.

It is known to clean such felts by means of a "reciprocating shower". This is usually an elongate member which extends above and acrossthefelt, which is normally in conveyor beltform. Holes are provided onthe underside ofthe elongate member from which jets of water issue onto the felt in order to clean it. The shower is provided with drive means to enableitto reciprocate back and forth across the felt in a direction generally transverse to the direction of movement ofthe conveyor belt, so washing all areas of the felt.

One of the major problems which exists in presently known motive power units for such showers is the length oftimetaken to reverse the direction of motion ofthe reciprocating shower at each extreme of movement. The time taken when using prior art motive power units can be so long that, in the case of the reciprocating shower, jets of water are directed on the same areas of the felt for such a length of time that the felt becomes shredded.

The present invention provides a liquid dispensing apparatus for use in paper production, comprising an electronically controlled stepper motor arranged to undergo periodically reversing rotational motion, a means arranged to translate the rotational motion of the stepper motor into linear motion, and a liquid dispensing member connected to said means wherebysaid liquid dispensing member is caused to reciprocate uniformly in response to periodically reversing motion of the stepper motor.

The use of the electronically controlled stepper motor has the advantage that a reciprocating movement is provided which is both constant and extremelyfast reversing.

The electronic circuitry utilised preferably counts pulses which drive the stepper motor and reverses the motor after a set number of pulses have been counted.

Preferably, the number of pulses which are counted before reversal ofthe motor occurs can be pre-set, so thatthe length overwhichthe liquid dispensing member reciprocates can be pre-set.

Preferably, means are also provided for varying the rotational speed of the stepper motor, so that the reciprocating speed ofthe liquid dispensing member can be varied.

The meansfortranslating the rotational motion of thesteppermotorinto linear motionforthe liquid dispensing member is preferably a ball screwassem blyconnected between the stepper motor and the receiprocating member.

The use of electronic circuitry to provide the reverse facility gives the added advantage that it is possible to useasthe meansfortranslating rotational motion into linear motion a standard ball screw of lightweight yet strong design, thereby producing a compact motive power unit of relatively small size.

The type of stepper motor preferably utilised in the invention is the type such as, for example, the SIGMA SERIES 20 20/42700 200F06 motor.

On switch on of the apparatus the stepper motor is preferably arranged to rotate in a predetermined direction, sothatthe liquid dispensing member moves linearly in a predetermined direction at switch on, and there is provided means responsive to the apparatus reaching a predetermined position during the motion to cause reversal of the stepper motor and resetting ofthe counter circuitry. The means respon sivetotheapparatus reaching a predetermined position is preferably a Hall switch which is activated by the meansfortranslating into linear motion.

The apparatus is also preferably provided with a motion detecting means to detect whether or notthe apparatus is in motion and circuitry means responsive to the motion detecting meansforcontrolling various functions ofthe apparatus. For example, if the motion detecting meansdetectsthatthere is no motion of the apparatus the circuitry means can be arranged to cause the liquid dispensing means to cease dispensing liquid. The motion detecting means preferably comprises a Hall switch arranged to detect motion of said means fortranslating into linear motion.

Further features and advantages ofthe present invention will become apparentfrom the following description of an embodimentthereof byway of example only with reference to the accompanying drawings, in which; Figure 1 shows a perspective view in schematic form of a motive power unit according to the present invention applied to a reciprocating shower unitfor cleaning felts.

Figure 2 shows a sectional plan view of a ball screw assemblyfortranslating rotational motion into linear motion.

Figure 3 shows a block diagram in schematic form of a possible electronic circuit for controlling the motive power unit according to the present invention.

With reference to Figure 1 ,felt 1 for use in a paper making process is shown in conveyor belt form, being moved in the direction indicated by the arrow A past a liquid dispensing apparatus designated generally by reference numeral 100. A liquid dispensing member, reciprocating shower head 2 which extends above and across the felt conveyor belt land is provided with holes on its underside from which jets 3 of water issue in order to wash the felt 1. The water is introduced to the shower head 2 e.g. at either ofthe ends indicated by the arrows B.

A motive power unit assembly 4,5,6 isfixably mounted adjacentthefelt 1 to cause reciprocating of the shower head. The assembly 4,5,6 includes a The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

stepper motor 6 mounted atthe end ofthe assembly4, 5,6 remote from the felt 1. The stepper motor 6 drives a rotary shaft 15 which is rotatably coupled to a ball screw assembly 4. The rotary shaft 15 drives a ball screw7 (Figure 2) in the ball screw assembly so giving an oscillating motion to a tube 9 slidably mounted within the ball screw assembly4. The tube 9 is connectedto one end ofthe shower head 2 by means of connecting members 10 and 5 and the oscillating motion ofthetube 9 causesthe showerto oscillate back and forth acrossthefelt 1,so washing all areas of the felt.

Figure 2 shows the ball screw assembly4 in greater detail. A hollow elongate housing 40 is provided, within which a ball screw7 is mounted on bearing 41 and 43 situated at either end ofthe housing 40, so that the ball screw7 extends within the housing 40 for most of its length.

Atube 9 is slidably mounted within the housing 40.

One end ofthetube9 is fixedly mounted on a member 8which is itself movably engaged with the threads of the ball screw 7. The tube 9 isfurthersupported along its length by being slidably mounted on a bearing 43 provided at one end ofthe housing 40. A guide track 11 is provided on the inner surface ofthe housing 40 and extends most ofthe length thereof. The track 11 engages a protrusion extending from the periphery of the member 8. In this way, when the ball screw7 is rotatably driven by the rotary shaft 15, the protrusion 11 preventsthe member 8 from rotating. Instead, as threads within the member 8 are engaged with the threads ofthe ball screw 7, the member 8 is forced into linear motion along the length ofthe ball screw7.

When the direction of rotation ofthe ball screw 7 is reversed the direction of linear rotation ofthe member 8 is reversed. The linear motion ofthe member8 is communicated to the tube 9 which moves in and out of the housing 40 with a telescopic action. The connecting member 10 isfixably mounted on the end ofthe tube 9 remote from the member8. The shower head 2 isfixed to the connecting memberforreciprocating motion.

The coupling member 12 is coupled to the rotary shaft 15 (figure 1), so thatthe rotary motion of the rotary shaft 15 is communicated to the ball screw7.

Figure 3 shows an example electronic circuit in block diagram form which may be used to control the rotation ofthe stepper motor 6.

A counter 21 is arranged to countthe regular pulses which are provided to drivethe stepper motor 6circuitry used to drive stepper motors bythe generation of regular pulses is known in the artofstepper motors. A given number of pulses, for example 400 will drive the stepper motorthrough one complete revolution.

The counter 21 is connected to a stepper motor control unit 22. a hall switch 20 (also shown in figure 2) is connected to the counter 21 and stepper motor control unit 22.

In operation stepper motor 6 is switched on and the stepper motor control 22 causes the stepper motor 6 to rotate in a prldetermined direction such thatthe ball screw assembly 4 contracts. On full contraction of the ball screwassembly4the unit actuates the Hall switch 20 causing stepper motor control 22to reverse the direction of rotation of the stepper motor 6. At the sametimethe counter circuit 22 is activated and starts counting the drive puses forthe stepper motor 6. After a preset number of counts has been reached the counter22 causes the stepper motor control 21 to reverse the direction of rotation ofthe stepper motor 6. Atthe same time the counter is reset and reset cycle then continues until the power is removed from the unit.

If the stepper motor 6 stalls for some reason, such as becoming overloaded for instance, it is necessary that the watersupplyto the shower head 2 be turned off in orderto preventthefelt 1 from becoming shredded.

To this end a motion detector 24 is provided which detects whether or not the reciprocating tube 9 is in motion.Whenthetube9isin motion a relay25, connected to the pump or valve control forthe water supply, is kept activated. When the tube 9 is not in motion the relay 25 is no longer activated, causing the pump or valve control to shutthe water supply off. the motion detector may also be arranged to switch the motor off when motion is no longer detected.

The detection of motion ofthe tube 9 can conveniently be performed by providing further Hall switches 50,51 in the ball screw assembly 4 (figure 2) arranged to give out pulses on motion ofthetube 9. As long as pulses are given out bythe Hall switchesthe relay 25 remains activated.

The countercurcuit2l may be arranged to be pre-programmable so thatthe stepper motor 6 can be reversed after any given numberofcountssothatthe distance which the liquid dispensing member traverses in reciprocation can be varied.

The stepper motor 6 is preferably arranged to have an adjustable speed of rotation, so thatthe liquid dispensing member has a variable speed of stroke so that it may be setforthe best results. For example, a potentiometer adjustable via a rotary switch could be provided forvarying the speed ofthe stepper motor 6.

Atfull load it is estimated thatthe apparatus in accordance with the present invention will take less than 15 milliseconds to fully reverse at 3.75 mmls reciprocator movement. This means thatthe shower head does not remain atthe extremes of its reciprocating movement long enough to cause shredding of the felt.

Preferably, it is a basic characteristic ofthe stepper motor6thatitwill stall and notoverheatwhen its design torque is exceeded. The mechanical components ofthe rest ofthe unit are preferably designed to withstand loads far in excess of the capabilities of the stepper motor. Therefore it is not possible to overload the mechanical parts ofthe unitwhen connected in eitheran incorrectwayortoa badly aligned showeror to a showerthat has become gummed up, and the stepper motorwill stall before any damage occurs.

Preferably, the electrical power ofthe apparatus in the wet area is at a safe voltage. For example the mains in the control unit (to be placed outside the very wet area) may be 240v or 120v ac., 50 or 60 Hz, whereas the outputfrom the control unit the stepper motor and controls may be ata maximum of 24V.

The electrical control circuitry forthe stepper motor 6 may be housed at any convenient position in or around the motive power unit.

It will be apparent thatthe power unit need not be connected to the liquid dispensing member as shown and described, but could be connected in other ways.

For example, the tube 9 could be directly connected to the reciprocating member 2, without the connecting members 5 and 10.

Itwill also be appreciated that Hall switches need not be used to detect whether or not the tube 9 is in motion. Othertechniques could be utilised. Also motion of other parts of the apparatus, not only the means for translating into linear motion, could be detected.

Also, the distance which the liquid dispensing member traverses in reciprocation need not be controlled by counting the pulses provided by the stepper motor drive means. Depending upon the required operating parameters of the unit a rotary disc having regularly spaced holes adjacent its perimeter could be utilised. The disc would be arranged to rotate coaxiallywith the rotary shaft 15 and the number of rotations ofthe disc counted-for example by providing a means for counting the holes in the disc periphery every time a hole passes adjacent it. The number of rotations of the disc could be used to control the extent of motion of the reciprocating member.

It will also be appreciated that other means could be used to control the pump or valve mechanism - not only a relay- and that the motion detector could be used forthe control of other external devices-not only pumps or valves.

In some circumstances it may be advantageous to control the rate of flow of liquid from the liquid dispensing member in accordance with the speed of the member in order, for example, to prevent uneven washing ofthe felt used in the paper production industry. For example, the rate offlow of liquid could be reduced as the speed ofthe member decreases so that at either extreme ofthe reciprocating motion liquid flow is reduced, preventing over-washing ofthe edges of the felt.

Claims (12)

1. Liquid dispensing apparatus for use in paper production, comprising an electronically controlled stepper motorarrangedto undergo periodically reversing rotational motion, a means arranged to translate the rotational motion ofthe stepper motor into linear motion, and a liquid dispensing member connected to said means whereby said liquid dispensing member is caused to reciprocate uniformly in response to periodically reversing motion of the stepper motor.

2. Liquid dispensing apparatus in accordance with claim 1, wherein there is provided counter circuitry arranged to count pulses which drive the stepper motor, and stepper motor control circuitry responsive to the counter circuitry counting a pre-determined number of pulses to cause reversal of the motion of the stepper motor.

3. Liquid dispensing apparatus in accordance with claim 2, wherein each time the stepper motor reverses the counter circuitry is reset.

4. Liquid dispensing apparatus in accordance with Claim 3, wherein the counter circuitry is pre-programmable so as to enable adjustment of said predetermined number, whereby the distance overwhich said liquid dispensing member reciprocates may be adjusted.

5. Liquid dispensing apparatus in accordance with claims 3 or 4, wherein the stepper motor is arranged to rotate in a predetermined direction when it is initially switched on, whereby the liquid dispensing member moves linearly in a predetermined direction at switch on, and wherein there is provided means responsive to the apparatus reaching a predetermined position during the motion to cause reversal ofthe stepper motor and resetting ofthe counter circuitry.

6. Liquid dispensing apparatus in accordance with claim 5, wherein said means responsive to the apparatus reaching a predetermined position is a Hall switch which is activated bythe means fortranslating into linear motion.

7. Liquid dispensing apparatus in accordance with any preceding claim, wherein there is provided a motion detecting means for detecting whether or not there is any motion of the apparatus, and circuitry means responsive to said motion detecting means for controiling various functions ofthe apparatus.

8. Liquid dispensing apparatus in accordancewith claim 7, wherein the motion detecting means comprises a Hall switch arranged to detect motion of said meansfortranslating into linear motion.

9. Liquid dispensing apparatus in accordance with claims 7 or8, wherein the circuitry means is arranged to cause said liquid dispensing means to cease dispensing liquid in response to said motion detecting means detecting that there is no motion.

10. Liquid dispensing apparatus in accordance with any preceding claim wherein said means for translating into linear motion is a ball screw assembly.

11. Liquid dispensing apparatus in accordance with any preceding claim, wherein there is provided means for varying the rotational speed ofthe stepper motor, whereby the reciprocating speed of the liquid dispensing member can be varied.

12. Liquid dispensing apparatus substantially as herein described with reference to the accompanying drawings.