AU597430B2

AU597430B2 - Method and apparatus for the controlled release of metered quantities of lubricant

Info

Publication number: AU597430B2
Application number: AU79317/87A
Authority: AU
Inventors: Volker Ingo Glasel; Gunther M. Voss
Original assignee: Dr Karl Thomae GmbH
Current assignee: Boehringer Ingelheim Pharma GmbH and Co KG
Priority date: 1986-10-03
Filing date: 1987-10-02
Publication date: 1990-05-31
Anticipated expiration: 2007-10-02
Also published as: EP0262538B1; ES2017486B3; BR8705245A; JPS6393500A; EP0262538A1; AU7931787A; DE3633646A1; DD264188A5; ATE55726T1; DE3764440D1

Abstract

1. Process for the controlled release of metered lubricating liquids or suspensions in applying a coating of lubricant to mechanically stressed zones of pressing tools in tablet-making machines, in which the lubricant solution or suspension is metered to one or more liquid valves (F) from an unpressurised storage container (V) by means of a pump (P) operating without pulsations, in such a way that the metering is in synchronism with the cadence of the table-making machine, characterised in that an under- or over- pressure prevailing at the pump outlet and measured against a rated pressure brings about a change in the times of opening of the liquid valves (F), or optionally changes in pressure may be equalised upstream of the pressure gas valves (L) by changes in the times of opening these pressure gas valves.

Description

.3 5)9'743 0 Australia Form PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. CI: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT SN~me of Applicant: DR. KARL THOMAE GmbH Ardress of Applicant: D-7950 Biberach an der Hiss, Federal Republic of Germany.

Actual Inventor: VOLKER INGO GLASEL and GUNTHER M. VOSS Address for Service: CALLINAN AND ASSOCIATES, Patent.Attorneys, of 48-50 Bridge Road, Richmond, State of Victoria, Australia.

CoplteSpciictin orth ivetin nttld: "METHOD AND APPARATUS FOR THE CoplteSpciictin orth ivetin nttld: CONTROLLED RELEASE OF M1ETERED QUANTITIES OF LUBRICANT"1 The following statement Is a full description of this Inven~tion, Including the best method of performing it known to Note. The description Is to be typed In double spacing, pica typo face, In an area not exceeding 250 mm in depth~ and 160 mm In width, on tough white paper of good quality and It Is to be Inserted inside this form, la The present invention relates to a method and apparatus for the controlled release of metered quantities of lubricant, and in particular for coating the mechanically stressed zones of pressing tools with lubricating liquids and suspensions.

DE-Al-33 12 634 describes a method and apparatus for dotting moulding tools with droplets of liquid or suspended lubricants in the manufacture of blanks in the pharmaceutical, food or catalyst fields.

Pressurised lubricant solutions or suspensions and pressurised gases are fed alternately through .t tt I c capillaries connected to alternating single-substance S*nozzles so that drops of lubricant are formed under a gas jet at the surface of the nozzles and these drops are applied to specific zones of the pressing tools. The apparatus comprises fast-acting valves S. for the brief release of pressurised gases and 1 r lubricating liquids or suspensions, the lines leading away from a gas valve and a liquid valve joining up in front of a capillary and a single-substance Snozzle is provided at the end of each capillary.

The capillaries together with the single substance nozzles are housed in specific arrangements in so-called dotting shoes. In this process, the quantity of lubricant required is taker from a f pressurised container and fed or metered into the capillaries in question by means of the liquid valves.

It has been found however that the throughflow rate of the liquid valves vary in the long term, e.g. by changes in the valve seat, from the throughflow rate originally determined and adjusted, for a i 1 ri e 1 111

I

2 given specific time of opening. This deviation has hitherto been corrected by determining the quantity of liquid delivered per unit time by monitoring the quantity of liquid in the storage container by means of a balance and correcting the valve opening times accordingly if there are any deviations.

The Yighing process required for this, which is affected by the strong vibrations of the press, is a drawback. The speed of rotation of the tablet press also has to be taken into consideration during the monitoring since any change in the number of pressing cycles would also change the quantities delivered per unit time through the liquid valves.

In the method according to the above application it is essential for the liquid container to be under high pressure. If the solvent or suspension agent is a low alcohol, the pressurised container constitutes a safety hazard. In addition, each time the system has to be topped up, the entire system has to be evacuated and re-set before it is started up again. It should also be mentioned that hiLherto it has not been possible to shorten this process since there is no throughflow measuring system for measuring the tiny quantities required (the smallest throughflow quantity which can be monitored is about 3 litres per hour).

Viewed from one broad aspect the prenent invention provides a method for the controlled release of metered quantities of lubricant in which lubricant and pressurised gas are supplied to a nozzle for application to a pressing tool, the method comprising supplying lubricant solution or suspension to a pulsed liquid valve by means of a pump, controlling the delivery rate of said pump in accordance with the operating rate of said pressing tool, monitoring the pressure differential across said valve, and adjusting the opening time 4 44 t 4 4 4 .4 4 I 44 Al1 l 3 of the valve if said pressure differential deviates from a predetermined value.

Preferably, the delivery of the pump is measured by a tachogenerator the ouput signal of which is fed to a computer, the computer compares the output signal and a signal indicative of the tool rate with a predetermined ratio of tool rate to pump delivery, and the computer causes the pump delivery to be varied to maintain this ratio.

In one preferred embodiment the pressure differential across the liquid valve is detected by means of a differential pressure measuring system the output signal of which is fed to the computer, and the computer compares the pressure signal with a predetermined value and causes the opening tim of said valve to be varied until said predetermined value is achieved.

If desired the pressurised gas is supplied through a gas valve and variations in the pressure across said gas valve from a predetermined value are detected and used to adjust the opening of said valve so as to prcduce constant gas jets when the gas valve is opened.

Viewed from another broad aspect the present 25 invention relates to apparatus for the controlled release of metered quantities of lubricant comprising a pump for supplying lubricant solution or suspension to a liquid valve, means for controlling the delivery of said pump in response to the operating rate of the pressing tool, means for detecting the pressure differential across said liquid valve, and means for varying the opening time of said valve in response to said pressure differential to maintain said differential at a predetermined value.

The apparatus preferably comprises an unpressurised storage container which can be topped up continuously

I

i f :j i ki~ g t ;t te IIIr tP~t tII I( 4 4 and which is connected via a line to the input of a pump which operates without pulsations. The pulsation-free pump is preferably a geared pump, e.g. having gear wheels with inclined teeth consisting of self-lubricating plastics material such as Teflon.

The outlet from the pump leads as a pressure line to one or more liquid valves; the pressure line preferably contains a differential pressure measuring system known per se which operates, for example, hydraulically and directly or pneumatically and indirectly; any differences in pressure measured relative to a preset or given pressure (rated pressure) are converted into electrical values and these are fed into a computer or comparator. The computer monitors and compares the incoming values with the rated values already fed in. If pressure variations exceed a certain amount, the control times of the liquid valve(s) are varied accordingly so as to shorten or lengthen the valve opening times. The differential pressure may be measured, for example, by so-called differential pressure sensors which can measure to a precision of up to plus or minus Piezo-resistant sensors of this kind convert 4. the mechanical pressure magnitude proportionally *too 25 into an amplified output signal from 4 to m and the measuring range covers, at most, 0 to 1000 bars.

"S In one embodiment, the pulsation-free pump is equipped with a drive component, e.g. a low voltage DC motor, whilst a contact-free electronic regulating device which acts on the speed of the pump motor continuously compares the rated voltage, which is set up by means of a potentiometer, with the voltage of a tachogenerator coupled to the drive shaft and regulates the speed of the pump motor accordingly. At the same time, the speed of the pump, which is independent of load and mains Li 5 fluctuations, is compared with the cadence or operating frequency of the tablet-making press by means of the computer and if necessary adapted thereto.

The first adjustment of the pump delivery, carried out by measuring in litres, is fed into the same cmifputer for the valve control, coupled to a given cadence of the tablet making machine. This adjustment operates as a closed regulating circuit and by means of its feedback system compensates for any fluctuations in the mains supply and also any fluctuations in load.

In order to compensate for any changes in the valve seats of the pressurised gas valves a differential pressure measurement may be used again, by means of suitable components, the data from which are compared by the computer, whilst the length of the program-dependent periods of opening of the pressurised gas valves are varied so that the gas jets produced are always constant (the same volume of gas for the same lenth of time).

The apparatus according to the invention has the advantage that as individual nozzles begin "to be blocked up the pressure in the line between t the pump and the liquid valves increases argd, after the pressure difference has been detected by the *#4Is4 computer, the opening times of the valves are extended S: as necessary; this ensures that the same quantity a of lubricant continues to be released to the relevant zones of the pressing tools. However, if the differential pressure increases beyond a certain threshold, a fault signal will be produced. The same applies to the reverse procedure, when the times of opening of the valves are shortened if the differential pressure falls; if the differential pressure drops by more than a certain amount below the rated pressure, again a fault signal is produced.

I- 6 An embodiment of the invention will now be described by way of example and with reference to the accompanying drawing in which Fig. 1 is a schematic plan of a lubricant supply system.

The lubricant solution or suspension is stored in an unpressurised storage container V. The lubricant is drawn from the storage container V by means a pump P along liquid line f. The pump supplies the lubricant from the container V to a liquid valve F after which the liquid line f divides to supply two nozzle assemblies each containing five nozzles.

The liquid line f includes, bet ,2en the pump P and the valve F, a differential pressure measuring system D for measuring the differential pressure across the liquid valve F, This pressure measuring system may be of a conventional type, e.g, hydraulic manometers or differential pressure gauges.

SThe output line from the liquid valve leads into a mixing chamber or into a fork into which gas inlet lines controlled by gas valves also lead; S connected to the end of this mixing chamber, which *may also be in the form of a mixing channel or fork with an adjacent mixing channel, is the nozzle 25 assembly which consists of a cavity of a specific volume and has nozzles for delivering the droplets.

The air or gas valves are controlled by the computer 1 *(to be dest'ibed below) so that they synchronously, Sbut at staggered times, deliver a defined gas 30 jet which serves to produce a bulge in the meniscus at the ends of the nozzles, to release the droplets and accelerate them toward the parts to be lubricated.

The lubricant supply system is controlled by a computer R. Basically the control system comprises two feedback circuits; a first feeback circuit (indicated by arrows---- comprises a kichogenerator T, computer R, potentiometer M, nY 44 *r 4 4*44 4 4'.

*4 4 44 4* 4 44 7 pump dri-'e motor A and pump P; the second feedback circuit (indicated by hatched arrows j-jt) comprises the differential pressure measuring system D, computer R and liquid valve F.

The first feedback circuit varies the lubricant delivery by the pump in response to the operating rate of the pressing machine. The delivery of the pump is monitored by means of a tachogenerator running concurrently with the pump in order to maintain a constant adjustment, the tachogenerator readings are fed into the computer which compares the findings with the ratio of machine operating frequency to lubricant delivery already established, fed in through a potentiometer, and if there are 15 any deviations caused by changes to the machine operating cycle, the computer causes a suitable correction to be made in order to restore the ratio originally set up via a potentiometer which controls the drive A of the pump.

20 The drive is linked to the above mentioned computer, which also operates the actuation system for the liquid valve, in such a way that the actuation period of the valves is always adapted to the pump performance. This procedure ensures that once a particular throughput of lubricating fluid has been selected it is maintained. The liquid valves no longer meter but merely "divide up" a quantity of liquid or suspension which has previously been metered by the pump.

The second feedback circuit varies the time for which the liquid valve is open in order to ensure constant throughflow regardless of any deterioration in the performance of the valve. If there is any change to the liquid valve the valve seat) and as a consequence the throughflow rate alters, -8this control is used to correct the rfesul'ting deviations, specifically by measuring the pressure difference in the system between the pump outlet and the entry to the liquid valve, by comparison with an adjusted pressure set up at the start. If the valve seating of the liquid valve has changed so that, for the same given time of opening, it now meters less then the required quantity of liquid, the pressure between the valve and the pump will automatically increase or, if the valve seat has worn so much that the throughflow rate has Increased, the pressure will drop. This differential pressure can easily be determined e.g. by means of hydraulic manometers, differential pressure gauges, and is then digitally displayed by a computer and processed so that it shorten~s or lengthens the valve opening times accordingly.

The quantity of lubricant required is guaranteed by the lubricant pump operating synchronously with the machine rate and not, as before, by the valves which are only coded at the beginning and whose throughflow rates can change, as already explain~ed.

It will be seen that, at least in preferred forms, the present invention provides several advantages over the prior art,. Firstly, there is no need for a pressurised container holding the lubricating liquid or suspension, secondly metering is carried out automatically in synchronism with the rate of the machine, and thirdly the excess pressure prevailing at the pump outlet is used for measurement of a differential pressure, relative to a given pressure, and if any deviations are found the programdependent opening times of the liquid valve are aqrtrected. This ensures that the tool surfaces are guaranteed to receive the quantities5 of lubricant required.

1- II i i L~ __I 9 Example 00 00On 9084 0r 0 00 4+ o 0 0090 0 00 0>0 0 Using a tabletting machine (model 3000 from Messrs. Wilhelm Fette GmbH, D-2053 Schwarzenbek) fitted with 2 lubricant stations each having 2 nozzle sets of 5 nozzles each, compressed tablets of acetylsalicylic acid and lactose/starch (diameter 19mm) were prepared. The metering pump ran synchronously to the speed of revolution of the tabletting press under the maximum liquid pressure of 6 bar.

A sensor detected the starting time on a top ram. A liquid valve opened for a time of 2.6 ms, and at the same time a delay for the gas valve started (about 2.4 ms delay time). After the liquid valve had closed, a pressure sensor fitted between the pump and the valve sensed any pressure differentials, 15 which may have arisen, within the range of and, if there were deviations, a microprocessor balanced the opening time of the liquid valve.

With the closing of the liquid valve, the air valve started the opening process, Mter expiry of the delay, the opening time being 2.4 ms. Here again, a fitted sensor automatically regulated any valve seat wear which might have occurred. The metering step thus induced lubricated the die edge. After the coded and, if necessary, readjusted air valve time had expired, the air valve closed. A coded pause time causad the above steps to be repeated.

At a speed of revolution of 1 m/s o£ the tabletting disc, the second shot of lubricant hit the centre of the die, and the third shot hit the opposite die edge. A coding switch determined the number of required repeats of the cycles before a new tap at the ram shaft. The lubricant fluid was under a pressure of 2.8 bar, and the air unden 3.3 bar.

00 O 00 0000 0 0 0 41 10 At 180,000 cycles/hour and with 2 lubricant stations each having 2 nozzles sets with 5 nozzles each, the pump throughput was 320 ml/hour in total or 80 ml per hour and nozzle set of 5 nozzles.

The lubricant consisted of 4% by weight of stearic acid and 6% by weight of polyoxyethylene sorbitan monooleate in ethanol.

Under the same compression force as in a tablet compressed by conventional methods, the breaking strength of the tablet was 40% higher.

Since the granules were not mixed with a hydrophobic lubricant, the disintegrating agent was able to deploy its full activity. The disintegration time of the tablet was thus reduced from 65 to 9 seconds.

I t S

I

4 R*

Claims

1. A method for the controlled release of metered quantities of lubricant in which lubricant and pressurised gas are supplied to a nozzle for application to a pressing tool, the method comprising supplying lubricant solution or suspension to a pulsed liquid valve by means of a pump, controlling the delivery rate of said pump in accordance with the operating rate of said pressing tool, monitoring the pressure differential across said valve, and adjusting the opening time of the valve if said pressure differential deviates from a predetermined value.

2. A method according to claim 1 wherein the delivery of said pump is measured by a tachogenerator S 15 the ouput signal of which is fed to a computer, the computer compares said output signal and a S% signal indicative of the tool rate with a predetermined ratio of tool rate to desired pump delivery rate, and wherein said computer causes the pump 20 delivery rate to be varied to the desired value Sif necesary. S3. A method according to claim 2, wherein said pressure differential acro quid valve is detected by means of a 4d erei .l41 pressure measuring system the output of which is fed to said computer, and wherein said c t-.3ter compares the pressure signal with a predetermined 44 value and causes the opening time of said valve to be varied until said predetermined value is achieved.

4. A method ecojrding tzo any prE^edin e1^: wherein the pressurised gas f supplaed bhrough a gas valve and who in the pressure i 12 across said gas valve from a predetermined value are detected and used to adjust the opening of said valve. A method for the controlled release of metered quantities of lubricant substantially as hereinbefore described with reference to the accompanying drawing.

6. Apparatus for carrying out the method of any preceding claim comprising a pump for supplying lubricant solution or suspension to a liquid valve, means for controlling the delivery of said pump in response to the operating rate of the pressing tool, means for detecting the pressure differential across said liquid valve, and means for varying the opening time of said valve in response to said pressure differential to maintain said differential at a predetermined value.

7. Apparatus according to claim 6 comprising means for detecting the operating frequency of the tool, means for monitoring the delivery of said pump, means for comparing the operating frequency with the pump delivery, and means for adjusting the purtip delivery as a result of said ",comparison to maintain a given relationship therebetween.

8. Apparatus according to claim 7 wherein the pump delivery is measured by a tachogenerator the 2 output of which is fed to a computer which in turn A controls the drive of said pump.

9. Apparatus according to claim 8 wherein the means for detecting said pressui-e differential sends a signal to said computer and said computer varies the opening time of said liquid valve in response thereto. 13 Apparatus according to claim 8 or 9 wherein the computer varies the opening time of a gas valve in response to variation in pressure across said gas valve.

11. Apparatus according to any of claims 6 to comprising an unpressurised storage container for the lubricant.

12. Apparatus for the controlled release of metered quantities of lubricant substantially as hereinbefore described with reference to the accompanying drawing. D A T E D this 2nd day of October, 1987. DR. KARL THOMAE GmbH By its Patent Attorneys: CALLINAN AND ASSOCIATES i i: I W 1