GB2258629A

GB2258629A - Apparatus for joining plastics surfaces

Info

Publication number: GB2258629A
Application number: GB9216944A
Authority: GB
Inventors: Brian James Sheppard
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-08-09
Filing date: 1992-08-10
Publication date: 1993-02-17
Also published as: GB9216944D0

Abstract

The apparatus comprises a first jaw 28 movable by means of a solenoid towards a second jaw 24 to engage a component 32 such as a plastics tube, and away from the second jaw to permit the tube to be inserted or released from between the jaws. An HF or RF signal generator provides a signal to the jaw 28 for generating heat enabling surfaces of the tube to be joined. A thermistor is provided and positioned so as to be sensitive to jaw temperature. An operating circuit includes a control circuit responsive to the thermistor to control the operation of a timer. The timer is arranged to control the length of time that the solenoid operates to hold the tube 32 between the jaws. The jaws 24, 28 comprise an assembly in the form of a head 13 which can be detached from a housing 10 of the apparatus for ease of cleaning. <IMAGE>

Description

APPARATUS FOR JOINING PLASTICS SURFACES The invention relates to apparatus for joining plastics surfaces and is particularly, but not exclusively, concerned with apparatus for sealing plastics tubing.

It is known to provide sterile sealing of blood bags and connecting tubing. In such an application, the sterile seal must have a very high degree of consistency at the point of seal in order to prevent cracking, fusion or punctures in the plastics which would render the contents useless and could result ln internal or external contamination.

A knawn apparatus for producing sterile seals includes a pair of small jaws between which the component to be sealed is placed and a radio frequency (RF) or high frequency (HF) signal generator which applies a signal across the jaws to provide heat for sealing. Such an arrangement solidifies the plastic component at the local point of contact of its surfaces. Where large numbers of plastics components such as tubes are sealed one after the other with little time interval between, the application of the RF or HF signal gradually causes the jaws to overheat. Such overheating has an adverse effect on the plastics component in the region of the jaws which can give rise to the aforesaid cracking, fusions or punctures and one object of the present invention is to provide apparatus which will help to reduce that particular problem.

According to one aspect of the invention there is provided apparatus for joining plastics surfaces of a component or respective components comprising a first jaw movable towards a second jaw to engage the component or one of the components and movable away from the second jaw to permit the or each component to be inserted between or released from between the jaws, means for generating heat to join the surfaces, sensor means sensitive to the temperature of the first jaw and/or the second jaw, and control means responsive to the said temperature for controlling the sealing operation.

By utilising a sensor means in that way, the control device will operate so that heat is not applied to the or each component in such a way that cracks, fusions or punctures are likely to occur. The means for generating heat may be an HF or RF signal generator although fusion of the plastics surfaces may be from generated heating produced from the application of a laser or ultrasonic source.

The control means, which preferably includes electrical circuitry, may be arranged to control the length of time that the jaws remain in engagement with the component.

In that way, if the temperature of the jaws gradually increases through repeated use, the rise in temperature will result in a shorter contact time between the jaws and the or each component to maintain consistency of flow of the plastics material of the component.

Alternatively, or additionally, the control means can be arranged to control the said temperature for example, by controlling the heat generating means.

Where repeated use causes the temperature to rise: the rise in temperature will be sensed and the power or intensit of the HF or RF signal can be reduced so as to cause the temperature to fal and avoid inconsistent flow of plastics at the point of joining. Where the operating jaws are small, which is commonly the case where tubing for blood bags is being sealed, localised heating can build up quite rapidly resulting from the lack of bulk material.

The present invention is of considerable benefit in such a case and greatly reduces the risk of inconsistent and unreliable sealing in such plastic tubes.

The sensor means may be mounted on or adjacent a said jaw, for example the second jaw which is preferably fixed. The sensor means may conveniently be mounted on a heat conductive carrier for that jaw so that heat therefrom is conducted through the carrier to the sensor means. In that way, there will be a slight time lag between the temperature rise of the jaw and the sensing thereof by the sensor means and that may be advantageous in certain circumstances.

Further sensor means may be provided for sensing the temperature of the component or components. In that way signals from the plurality of sensor means can be compared and adjustments made in the control device for controlling the sealing operation.

Another problem which arises with apparatus for joining surfaces such as surfaces of tubes for blood bags is that cleaning of the jaws in situ or the dismantling of individual parts of a complete jaw assembly is too time consuming and expensive. Also on re-assembly there is a risk of mis-aligning the jaws. The need for cleaning arises if there is any leakage from the tube onto the surrounding jaw components and, if the blood is affected by high ric contaminants, it is most important that the contaminated components are thoroughly cleaned.

Cleaning in situ may result in an ineffective and a mere partial cleaning and may fail to remove contamination agents. An object of a further aspect of the invention is to reduce the problem of cleaning.

According to a further aspect of the invention there is provided apparatus for joining plastics surfaces of a component or respective components comprising an assembly of first and second jaws detachably mounted on part of the apparatus, the first jaw being movable towards the second jaw to engage the component or one of the components and being movable away from the second jaw to permit the or each component to be inserted between or released from between the jaws, and means for generating heat to join the surfaces.

The ability to detach the assembly from the operating means enables the complete jaw assembly to be cleaned away from the operating means by, for example, immersing the jaw assembly in a suitable cleaning and/or sterilising solution in order to effect the removal of all the contamination agents. Also, as the complete assembly is removed for cleaning, there is reduced risk of jaw misalignment on re-assembly, the jaws remaining in operational prciity.

Conveniently, the assembly is in the form of a sealing head which may be detachably mounted on a control box for housing other parts of the apparatus.

The assembly preferably includes a cover which can be detached either with the assembly as a whole or removed separately therefrom.

Operating means for the first jaw may comprise a reciprocable member to which the first jaw is detachably connected, e.g. by means of a screw arrangement or a locking or retaining pin arrangement.

In an arrangement according to the second aspect of the invention, the aforesaid temperature sensor means may be provided, the aforesaid control device being responsive to the temperature for controlling the joining or sealing operation.

In the first or second aspect of the invention or any of the consistory clauses relating thereto, detector means may be provided for detecting when a component is present between the members of the jaw. Such detector means may comprise one or more micro switches, one or more proximity sensors or one or more light sensing devices arranged such that a light beam will be cut by inserting the component between the jaws.

Monitoring means may be provided for indicating if the temperature sensor has become inoperative, for example, through disconnection or by means of a short circuit in associated wiring. The monitoring means may provide a warning signal which may be arranged to prevent further operation of the first jaw for a relatively longer time period and thereby prevent over-heating of the plastic surfaces to be joined.

The warning signal can be audible and/or visible.

Apparatus in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Fig.1 is a side elevation of part of a preferred form of sealing apparatus in accordance with the invention shown partly broken away, Fig.2 is a perspective view of the apparatus of Fig.

showing the way in which a sealing head of the apparatus can be removed, Fig.3 is a cross section through the sealing head of Fig.2 generally on the line III - III in Fig.4, Fig.4 is a cross section on the line IV - IV in Fig.3, and Fig.5 is a diagrammatic view of an operating circuit for controlling sealing.

The apparatus comprises a housing 10 containing operating circuitry and other components. The housing 10 has a front panel 12 which carries a sealing head 13. The sealing head has a back plate 14 (Figs.3 and 4) suitably connected to a side cover 15 formed with a slot 15a. The back plate 14 is attached to by means of screws 11 to a top-hat cross section mounting 17 and the sealing head 13 is detachably connected to the front panel 12 by screws 16. The mounting 17 has side sections 18, 19 which carry respective microswitches 20, 22. In the embodiment shown, the mounting 17 also carries a thermistor 23 and a fixed jaw 24 (constituting the aforesaid second jaw). A block 25 of PTFE or similar material is mounted against the backplate 14 and between the side sections 18, 19.The block 25 is formed with a first through bore 26 in which an operating rod 27 is slidably mounted. The operating rod is attached at its left hand end as shown in Fig.3 to another jaw 28 (constituting the aforesaid first jaw). The block 25 is formed with a second through bore 29 which slidably receives a stabilising pin 30 attached to the jaw 28. The through bores 26, 29 terminate at a counterbore 31 in the block 25.

The housing 10 contains a solenoid 33 having an operating member 34 shown diagrammatically in Fig.4 which is movable axially against the bias of a return spring 35 on application of current to the solenoid.

The operating member 34 is screwed to the right hand end of operating rod 27. Movement of the operating member 34 to the left as viewed in Figs.1 and 4, causes the jaw 28 to move towards the jaw 24. The operating member 34 moves into the counterbore 31 in the block 25 in order to close the jaws fully. To open the jaws, the current supply to the solenoid 33 is switched off and the operating member 34 returns to the right under the influence of the return spring 35.

The microswitches 20, 22 are connected to a controi circuit 36. The control circuit 36 forms part of control means of control means in the form of operating circuitry 41 of the apparatus shown diagrammatically in Fig.5 and which is powered via a mains transformer 42. The microswitches have respective operating arms 20a, 22a which are depressed by inserting a plastics tube 32 through the slot 15a and between the jaws 24, 28 and urging it downwardly against the operating arms. Once the operating arms 20, 22a have been depressed, the control circuit 36 transmits current to drive the solenoid 33 thereby causing the jaws to close on to the tube 32. A timer 37 controls the length of time that the jaws are closed and eventually switches off the current to enable the jaws to open.An RF or HF signal generator 38 transmits signal via the jaw 28 for a time determined by the timer 37. The signal generates heat in the tube 32 between the jaws to seal together opposite inside surfaces of the tube.

The thermistor 23 is connected to a circuit 39 associated with the timer 37 and which controls the operation of the timer. A monitoring circuit 40 is associated with the thermistor 23 and will provide a warning signal if the thermistor has become inoperative, for example, through disconnection or by means of a short circuit in its associated wiring.

As shown in Figs.1, 2 and 3, the wiring associated with the microswitches 20, 22 and thermistor 23 can be connected to the operating circuitry 41 within the housing 10 through a plug 60 locatable in a socket 60a on the housing 10. A position sensor latch 50 is provided to ensure that subsequent release of either microswitch arm 20a, 22a after the depression thereof to initiate sealing, will not interrupt the sealing cycle. The sealing head 13 and its operating solenoid 33 could be arranged as one unit from which the sealing head 13 is detachable and the control circuit 41 could be housed in a second and separate unit connected to the first unit by cabling.

In use, the apparatus is switched on by means of a switch (not shown) on housing 10, a tube 32 is inserted between the jaws 24, 28 so that the microswitch operating arms 20a, 22a close to start an operating cycle. The position of the depressed arms 20a, 22a correctly positions the tube 32 in reiation to the jaws 24, 28. The control circuit 36 then switches on the HF or RF frequency generator 38 which transmits current to generate heat in the tube 32.

Simultaneously, the control circuit 36 switches on the solenoid 33 to move the jaw 28 to the left against the tube 32 and the control circuit 36 operates the timer 37 to control the time that the jaws are closed to form a homogeneous bond or seal.

The thermistor 23 receives heat conducted from jaw 24 through the mounting 17 which is preferably made of metal. If the temperature rises above a desire maximum, the circuit 39 causes the timer 37 to reduce the closing duration of the jaw 28 to prevent overheating of the tube 32. Alternatively, or additionally, the timer 37 controls the HF or RF signal generator 38 so as to reduce the signal transmission time to the jaw 28. Initial setting of the timer 37 and/or the HF or RF frequency generator 38 can be carried out by means of manually operable controls (not shown) associated with the circuit 41.

In the event that the thermistor 23 becomes inoperative, for example, through disconnection or by means of a short circuit in its associated wiring, the monitoring circuit 40 may be arranged to control the timer 37 so that the solenoid 33 cannot close the jaw 28 for a long period of time. The monitoring circuit 40 may also be arranged to prevent the HF or RF generator 38 continuing to produce power to or across the jaws.

By sensing temperature as described above, the jaw 28 and the HF or RF signal generator can be operated accurately so that excess heat will not be applied to or generated in the tube 32 and the risk of cracks.

fusions or punctures which can arise through overheating is greatly reduced.

By utilising temperature detection, the apparatus facilitates a change in timing and/or the RF or HF heating signal in keeping with the plastic tube temperature. Where a plastic tube is held against the jaw 24 or after several seals have been made with a plastic tubing that has been stored at a low or near freezing temperature, then the sealing time period will be similarly extended. Also the level G, the RF or HF heating signal will be increased to accommodate the requirements of the lower temperature tube for consistent sealing.

Instead of providing microswitches 20, 22 it is envisaged that alternative sensors may be provided such as light transmission/sensitive devices or suitable proximity sensors.

In order to clean the head 13 safely and efficiently, it can easily be detached from the housing 10 by releasing screws 16, detaching operating rod 27 from, operating member 34 and unplugging the plug 60 from the socket 60a. The complete head 13 can then be immersed in a suitable cleaning and/or sterilising solution in order to effect removal of any contamination agents. If desired, the side cover 15 can be removed from the remainder of the head 13.

Also, if the sealing head 13 requires replacement, for example, when the jaws have become damaged, worn, heavily contaminated or pitted due to arcing from liquid or moisture present between the jaws, the old head can be removed and a new head easily attached.

It is envisaged that a further thermistor may be mounted on or in association with the jaw 28. The temperature difference between the two thermistors can be sensed and a comparison made with ambient temperature. In that way, if lent temperature increases or decreases, that in itself can then be accommodated so as not to have an adverse effect on the sealing cycle.

A still further thermistor may be provided, e.g., adjacent one of the microswitches 20, 22, which will sense the temperature of the tube 32 inserted between the jaws 24, 28. The output from that thermistor can then be compared to that of the thermistor 23 and/or the thermistor associated with jaw 28. The operation of the HF or RF signal generator and/or the closing duration of the jaws is then controlled in response.

That will be particularly useful where highly accurate temperature sensing is required.

If desired heat sensors other than thermistors could be used.

Instead of mounting a single heat sensor in association with jaw 24 it could be mounted in association with jaw 28.

It is also envisaged that the or each thermistor could be omitted altogether where, for example, a user requires only the advantages offered by the use of a detachable head. Also, the use of one or more thermistors is envisaged where the head 13 itself is not readily detachable as shown in the drawings.

Whilst specific reference has been made to the sealing of opposite internal surfaces of a plastic tube 32, the invention can be applied to the sealing together of separate plastics components.

Claims

1. Apparatus for joining plastics surfaces of a component or respective components comprising a first jaw movable towards a second jaw to engage the component or one of the components and movable away from the second jaw to permit the or each component to be inserted between or released from between the jaws, means for generating heat to join the surfaces, sensor means sensitive to the temperature of the first jaw and/or the second jaw, and control means responsive to the said temperature for controlling the sealing operation.

2. Apparatus according to Claim 1 in which the control means is arranged to control the length of time that the jaws remain in engagement with the component

3. Apparatus according to Claim 1 or 2 in which the control means is arranged to control the said temperature.

4. Apparatus according to Claim 3 in which temperature is controlled by controlling the heat generating means.

5. Apparatus according to any preceding Claim in which the sensor means is mounted on or adjacent a jaw.

6. Apparatus according to Claim 5 in which the sensor means is mounted on or adjacent the second jaw which is fixed relative to the first jaw.

7. Apparatus according to Claim 6 in which the sensor means is mounted on a heat conductive carrier for that jaw so that heat therefrom is conducted through the carrier to the sensor means.

8. Apparatus according to any preceding Claim in which further sensor means is provided for sensing the temperature of the component or components.

9. Apparatus according to any preceding Claim in which the first and second jaws comprise an assembly detachably mounted on part of the apparatus.

10. Apparatus for joining plastics surfaces of a component or respective components comprising an assembly of first and second jaws detachably mounted on part of the apparatus, the first jaw being movable towards the second jaw to engage the component or one of the components and being movable away from the second jaw to permit the or each component to be inserted between or released from between the jaws, and means for generating heat to join the surfaces.

11. Apparatus according to Claim 9 or 10 in which the assembly is in the form of a sealing head detachably mounted on a housing for other parts of the apparatus.

12. Apparatus according to Claim 9, 10 or 11 in which the assembly includes a cover which can be detached either with the assembly as a whole or removed separately therefrom.

13. Apparatus according to any preceding Claim in which operating means is provided for the first jaw, the operating means comprising a reciprocable member to which the first jaw is detachably connected.

14. Apparatus according to any preceding Claim in which detector means is provided for detecting when a component is present between the members of the jaw.

15. Apparatus according to Claim 14 in which the detector means comprises one or more microswitches.

16. Apparatus according to Claim 14 in which the detector means comprises one or more light sensing devices

17. Apparatus according to Claim 14 in which the detector means comprises one or more proximity sensors.

18. Apparatus according to any preceding Claim in which the control means includes monitoring means for indicating if the temperature sensor has become inoperative.

19. Apparatus according to Claim 18 in which the monitoring means provides a warning signal.

20. Apparatus according to Claim 19 in which the warning signal is arranged to prevent further operation of the first jaw for a relatively longer time period and thereby prevent over-heating of the plastic surfaces to be joined.

21. Apparatus for joining surfaces of a plastics component constructed and arranged substantially as described herein with reference to the accompanying drawings.