Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
  • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
  • B29C65/18—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated tools
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
  • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
  • B29C65/18—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated tools
  • B29C65/24—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated tools characterised by the means for heating the tool
  • B29C65/30—Electrical means
  • B29C65/305—Electrical means involving the use of cartridge heaters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/40—General aspects of joining substantially flat articles, e.g. plates, sheets or web-like materials; Making flat seams in tubular or hollow articles; Joining single elements to substantially flat surfaces
  • B29C66/41—Joining substantially flat articles ; Making flat seams in tubular or hollow articles
  • B29C66/43—Joining a relatively small portion of the surface of said articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/90—Measuring or controlling the joining process
  • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
  • B29C66/912—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by measuring the temperature, the heat or the thermal flux
  • B29C66/9121—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by measuring the temperature, the heat or the thermal flux by measuring the temperature
  • B29C66/91231—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by measuring the temperature, the heat or the thermal flux by measuring the temperature of the joining tool
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/90—Measuring or controlling the joining process
  • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
  • B29C66/914—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux
  • B29C66/9141—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the temperature
  • B29C66/91421—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the temperature of the joining tools
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/90—Measuring or controlling the joining process
  • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
  • B29C66/914—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux
  • B29C66/9141—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the temperature
  • B29C66/91431—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the temperature the temperature being kept constant over time
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/90—Measuring or controlling the joining process
  • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
  • B29C66/914—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux
  • B29C66/9161—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the heat or the thermal flux, i.e. the heat flux
  • B29C66/91641—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the heat or the thermal flux, i.e. the heat flux the heat or the thermal flux being non-constant over time
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/90—Measuring or controlling the joining process
  • B29C66/91—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux
  • B29C66/914—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux
  • B29C66/9161—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the heat or the thermal flux, i.e. the heat flux
  • B29C66/91651—Measuring or controlling the joining process by measuring or controlling the temperature, the heat or the thermal flux by controlling or regulating the temperature, the heat or the thermal flux by controlling or regulating the heat or the thermal flux, i.e. the heat flux by controlling or regulating the heat generated by Joule heating or induction heating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/90—Measuring or controlling the joining process
  • B29C66/96—Measuring or controlling the joining process characterised by the method for implementing the controlling of the joining process
  • B29C66/961—Measuring or controlling the joining process characterised by the method for implementing the controlling of the joining process involving a feedback loop mechanism, e.g. comparison with a desired value
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D23/00—Control of temperature
  • G05D23/19—Control of temperature characterised by the use of electric means
  • G05D23/1906—Control of temperature characterised by the use of electric means using an analogue comparing device
  • G05D23/1912—Control of temperature characterised by the use of electric means using an analogue comparing device whose output amplitude can take more than two discrete values
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D23/00—Control of temperature
  • G05D23/19—Control of temperature characterised by the use of electric means
  • G05D23/1906—Control of temperature characterised by the use of electric means using an analogue comparing device
  • G05D23/1913—Control of temperature characterised by the use of electric means using an analogue comparing device delivering a series of pulses
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D23/00—Control of temperature
  • G05D23/19—Control of temperature characterised by the use of electric means
  • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C66/00—General aspects of processes or apparatus for joining preformed parts
  • B29C66/90—Measuring or controlling the joining process
  • B29C66/94—Measuring or controlling the joining process by measuring or controlling the time
  • B29C66/949—Measuring or controlling the joining process by measuring or controlling the time characterised by specific time values or ranges

Definitions

• the invention relates to heating means and more particularly, but not exclusively, to means for controlling electric heaters for use in apparatus and heat sealing plastics packaging film.
• heating control means for controlling the temperature of a member to be heated by an electrical resistance heating element comprises means for generating a control signal proportional to a target temperature, means for generating a control signal proportional to the actual temperature of the member, means comparing the two control signals to gauge the temperature difference, and means responsive to the control signal comparison for switching a power supply to the heating element, the switching being such that the power supply goes On' and 'off at a variable frequency and that the 'on' phases are of variable duration, both dependent on the temperature difference. In this way, more power can be supplied to the heater element when it is relatively cold both by relative high switching frequency and by relatively long 'on' phases.
• both of said frequency and said duration can be at their permitted maxima; though there coul- , ⁇ *? course, be an initial stage of continuously applied electrical power, if desired for last and largest prescribed temperature difference above the target temperature both of said frequency and duration can be at their permitted minima.
• variation of said frequency is used in preferred embodiments of this invention, for relatively fine control, compared with use made of variation of said duration.
• variable control can be by way of further reductions of both of said frequency and said durations, say with minimum (short of complete switch off as could be further provided) for said durations at a higher further prescribed temperature difference above the target temperature than applies to minimum for said frequency.
• both of frequency and duration reductions may take place at or close to achieving the target temperature on heating up, and/or at the prescribed temperature difference for frequency reductions to start on heating up, and/or at a prescribed temperature difference representing minimum frequency; and there can be intermediate further prescribed temperature differences at which at least frequency reduction occurs.
• each of a stream of pulses at said frequency to trigger pulse length determining means effectively setting said durations, and further to have such duration setting pulses each triggered within the sequence from the trailing edge of the immediately preceding duration setting pulse in the sequence.
• Control of plural heat-sealing dies or die parts can be relative to individual control temperature sensing means associated therewith.
• This approach is perhaps preferable where characteristics of different dies or die parts and their heating elements are not sufficiently similar for a single temperature sensor to suffice, or their temperature requirements differ and they are individually available for association with temperature sensors.
• pulse lengths corresponding to application of electrical power, or even a proportioning of applied or available power could be set for different dies or die parts, whether because their said characteristics are different in known relative ways or because one or more of the dies or die parts are to be heated differentially.
• This approach is perhaps preferable where it is impractical to have individual temperature sensors, say where a desiredly hotter die part is in a sandwich structure between desiredly less hot die parts.
• Figure 1 is an overall block diagram for heat sealing die provision including three side-by-side heaters;
• Figure 2 is a diagram for plural heat sealing dies or die parts each with a heater;
• Figure 3 is a circuit diagram for one stage of means for setting voltage by reference to temperature difference.
• Figure 4 is another circuit diagram for changing control pulse duration directly according to temperature difference.
• Operation is based on measuring the difference between voltage signals arranged to represent a selected or target temperature and actual sensed temperature of a heat sealing die, and controlling switching signals for solid-state switching circuitry for supplying either AC or DC current to at least one heating element.
• FIG. 1 The block diagram of Figure 1 is first described for main components involved in controlling one heating element 10B of a heat sealing die 12 that actually has three heating elements as will be further described later.
• An electrical power source 14 is shown supplying the heater element 10B through a solid-state electronic switch 16B.
• the heat-sealing die is shown with an actual temperature sensor 18.
• Solid state electronic power switches are well-known operative for determining 'on' states by durations of control pulse signals, see line 20B for switch 16B. These control pulse signals are controlled as to both frequency and duration, see idealised pulses 22B that can vary in a controlled way as to length or duration of each and as to intervals between them, i.e repetition rate or frequency.
• Durations of the control pulse signals 22B are shown determined by voltage controlled pulse length/width setting circuit 24B, and initiations and repetition rate by voltage controlled oscillator 26.
• the circuit 24B and the voltage controlled oscillator 26 can and preferably do have base states, i.e. with no voltage signals on their control lines 28 and 30, for pre-set maximum control pulse duration and preset maximum frequency or repetition rate.
• Voltage control signals for the pulse duration setting circuit 24B and the voltage controlled oscillator 26 are shown coming from circuits 28 and 30, respectively.
• the circuits 28 and 30 can be of similar types, conveniently resistance ladder networks that give voltage output changes in steps and according to sequential energisation of plural inputs. For each of the circuits 28 and 30, five inputs are shown, see 32A-E and 34A-E, respectively.
• resistance ladder networks for pulse- length/width and frequency control (at circuit 24B and oscillator 26) proportional to control voltages following 7 decreasing temperature difference to the target temperature then increasing beyond, resistance ladder networks (as circuits 28 and 30) can be so arranged that more of their inputs (32A-E, 34A-E) are energised, see further below regarding Figure 3.
• Energisation of inputs 32A-E and 34A-E of the voltage setting circuits 28 and 30 for the circuit 24B and oscillator 26, respectively, is shown in accordance with outputs of comparator circuity 36 and 38, respectively.
• These comparator circuits 36 and 38 receive both of signals representing a selected or target temperature at branches from line 40 from temperature selector 42, and at branches from line 44 for actual heat-sealing die temperature from the temperature sensor 18.
• the comparator circuits 36 and 38 operate on, as mentioned above, a basis of energising lines 32A-E and lines 34A-E sequentially according to prescribed temperature differences between its inputs, which prescribed voltages extend from the actual temperature being below through to being above the target temperature.
• prescribed temperature differences and responses are as follows:-
• Second prescribed temperature difference say 2°C below the target temperature, for energisation of outputs 32B and 34A, thus second reduction of the control pulse duration by circuit 24B, and first reduction of the frequency or repetition rate of oscillator 26.
• Third prescribed temperature difference say 1°C below the target temperature, for energisation of output 34B thus second reduction of the frequency or repetition rate at oscillator 26.
• Fourth prescribed temperature difference say zero, i.e. when the actual temperature first matches the target temperature during heating up, for energisation of outputs 32C and 34C, thus third reduction of the control pulse duration by circuit 24B, and third reduction of the frequency or repetition rate at oscillator 26.
• effective available control pulse durations as above can be 30, 20, 10, 8 and 5 milliseconds and available frequencies can have periods as above corresponding to repetition rates of 30, 17, 15, 10 and 2 per minute.
• the comparators 36 and 38 can, as indicated, usefully be based on operational amplifiers, one for each output, say each arranged to change state for detected equality of input signals, then with the target temperature signal off line 40 subject to successive offsets. Suitable such offsets can be minus 100, minus 20, zero, plus 20 and plus 50 or 100 millivolts for the comparator 36; and minus 20, minus 10, zero, plus 10 and plus 20 millivolts, where the temperature sensor 18 and the temperature setting means 42 operate or have their outputs adjusted on the basis of 10 millivolts per degree Centigrade (Celsius).
• illustrated components as so far described can service a heat sealing die having a single heating element, or a heat sealing die or dies having plural heating elements all to be energised together.
• particular practical advantage is seen arising from separate individual driving of plural heating elements sequentially within each of single periods of the voltage controlled oscillator 26, see dashed pulses 22C, 22A following first solid pulse 22B in Figure 1.
• heating elements are to be similarly driven as indicated by solid lines 20A,B,C to solid-state switches 16A,B,C for heating elements 10A,B,C in Figure 1, and with control according to a single die surface temperature sensor (18), but with control signals for the lines 20A,B,C coming from successive stages (TB, TC, TA) of the pulse generator 24B, each preferably and conveniently simply triggered from trailing edge of the control pulse from the preceding active stage, as is readily achieved, say using Schmitt Trigger circuitry 24S between those stages.
• the voltage controlled oscillator 26 could have a successive phasing or stage operation or structure, see dashed extensions therefrom in Figure 1 with dashed connection to pulse generating stages that could then be independent of each other.
• Another way to achieve differential die/die part temperatures is and to adjust the lengths of control signal pulses on the lines 20A,B,C after they have left the circuitry 24, whether in accordance with different actual temperature sensors, or by pulse shortening, even pulse stretching, circuitry to utilise a single temperature sensor 18 and operate according to offsets representing known relative parameters or simply adjusted to be effective.
• Figure 1 shows such offsetting by way of pulse shortening circuitry, see dashed at 46A,C in lines 20A,C as is appropriate for a three heater elements and die part system (10A,B,C;12) as used for heat sealing and severing/ weakening within overall sealing or between two distinct seals, where the central die part (10B) will ordinarily require a higher temperature and it is convenient to set the flanking die part (10A,C) relative thereto.
• Ramp-action blocking amplifiers are suitable and may well be best provided as indicated adjustable units 46A,C. Alternatively, adjustment could be within the extended stages of the circuitry 24.
• At least provisions such as control pulse length adjustors can also be particularly useful in coping with a dies or die-parts system where there is differential heat loss/take-off, and in order to seek to maintain a steady desired temperature, as sensed at 18 (or some other characteristic if more appropriate) .
• Figure 2 shows a die system 52 with four heating elements 50A,B,C,D as may be applicable simply to a long heat sealing die, or to a die structure with more than one direction of required sealing, say an asymmetric L— or a U- or C- or V- configuration, and each with its own solid- state pulse length controlled switch 56A,B,C,D from common power supply 54.
• This arrangement is readily controlled by circuitry as described for Figure 1, indeed that Figure shows dashed extension of its control pulse generator circuitry 24 and/or voltage controlled oscillator 26 for four-way use.
• Figure 3 shows part of one suitable resistive ladder type control for the voltage controlled oscillator 26, for which its control voltage needs to decrease for lower frequencies.
• the related operational amplifier 60A has inputs 61A,62A for voltage signals representing actual and appropriately offset target temperatures, respectively, and output 34A going high when the actual temperature (61A) exceeds the target temperature (62A) as appropriately offset.
• transistor 65A will be switched into conduction and adjustable resistance of potentiometer 66A will be shorted out and replaced by lower resistor 67A in the emitter/collector circuit of the transistor 65A going to earth rail 68.
• a multi-stage cascaded ladder-type circuit like Figure 3 can be used for control pulse length/duration setting as at 28, which might then operate on an up or down ramping basis to convert the voltage concerned to time, specifically duration of control pulse.
• a single operational amplifier 70 has two inputs 71 and 72 for signals with voltage levels representing actual and target temperatures, actually conveniently some suitable offset from the target temperature, which will usually be below.
• the operational amplifier 70 has its output 74 taken to bases of transistors 75 and 76, the latter via inverter 77.
• the transistors 75 and 76 are connected with their emitter/collector circuits going in common to ground at 78 from different capacitors 79 and 80 alternatively cooperating with resistor 81 to set time constant for a suitable pulse duration setting circuit 24. It will be appreciated that the operational amplifier 70 will operate at some prescribed temperature difference to switch from capacitor 80 to capacitor 79 for a single reduction in control pulse length/duration. A change from 12 to 10 millisecond duration is found to be enough, with the switching at as low as 5°C below target, or at about 2°C, or as otherwise desired relative to any useful overlap with frequency changing, say as above described.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• General Physics & Mathematics (AREA)
• Automation & Control Theory (AREA)
• Control Of Temperature (AREA)
• Package Closures (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1992
  • 1992-05-27 GB GB9211249A patent/GB9211249D0/en active Pending
• 1993
  • 1993-05-26 EP EP19930910289 patent/EP0642409A1/de not_active Ceased
  • 1993-05-26 AU AU40852/93A patent/AU4085293A/en not_active Abandoned
  • 1993-05-26 CA CA 2136093 patent/CA2136093A1/en not_active Abandoned
  • 1993-05-26 WO PCT/GB1993/001086 patent/WO1993024302A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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