This invention relates to an improved press for fabrics, for example, a trouser press.

When pressing fabrics it is known that the higher the temper- ature and the greater the period for which heating is applied, the better the result produced. However, maintaining high temperature for a prolonged period is extravagant in energy consumption, and also involves a risk of hot spots due to uneven heating, which may cause localised marking of the fabric. Excellent results may also be obtained by the injection of superheated steam into fabric stressed under pressure, but the necessary equipment is cumbersome and expensive, and involves the operator in some risk.

The present invention overcomes these difficulties and provides a press, for example, a trouser press, which is efficient, reasonably economical in energy requirement, and has less risk of damaging the fabric or buring the operator than the above methods.

According to the present invention a fabric press comprises a press with a heating element, a temperature sensor and timing means, wherein the press includes a controller arranged to apply electrical power initially to the element for a boost period during which the press temperature is limited to boost temperature, and then, at the end of the boost period, to reduce the applied power and thereafter to control the power to maintain the press temperature substantially at a lower normal temperature until a pre-set time has elapsed.

Preferably the boost temperature is in the range of 65°C to 90°C and is reached at some time during a boost period of 10 minutes or less after switching on. At the end of the boost period power is preferably switched off, and the temperature allowed to fall to a normal temperature of in the region of 55°C to 65°C, at which it is maintained the pre-set time, preferably 15 to 45 minutes after switching on.

During the boost period, under the influence of the elevated temperature and the pressure due to the press, the crease is formed into the fabric. At the lower temperature the crease is set. The reduction in temperature effects a considerable saving

in power consumed, and also reduces the risk of damage to the fabric and of accidental burns to the user.

A controller suitable, inter alia, for the control of a fabric press as described above operates from an alternating current supply and is arranged to supply heating current to a heating element through a triac. The controller includes a micro¬ processor which operates during each cycle of the supply voltage to determine whether further power needs to be supplied to the heating element. When power is so required the microprocessor triggers the triac at the voltage zero marking the start of the next succeeding voltage cycle and causes it to supply power to the heating element for that complete cycle. By supplying power for complete cycles in this way unsymmetrical loading of the power supply is avoided. The invention will be further described by way of example with reference to the accompanying drawings in which:

Figure 1 is a curve of temperature as a function of time for a typical trouser press;

Figure 2 is a flow diagram of the trouser press control; and Figure 3 is a block diagram of the controller employed with the press.

Referring first to Figure 1, A represents the point at which the press is switched on, and it is assumed initially to be at room temperature. The supply of power to the heating element raises the temperature to a region marked B in the neighbourhood of 80 C, at which the creases are formed in the material, after some 8 minutes have elapsed from first switching on. At the point C in Figure 1 the power is shut off, and the temperature begins to fall until it reaches the pre-set normal temperature of 60/65 C, at which it is maintained by the controller for a further period until a time pre-set by the user, generally in the range of 15-45 minutes, has elapsed, after which the power is shut off.

Figure 2 is a flow sheet illustrating the operation of the controller. Initially, as represented by box 1 on the diagram, the times and temperatures required are set into the controller.

At 2 the temperature is checked to determine whether it has exceeded the applicable reference value; if not power is supplied to the heating element for one supply cycle as indicated at 3. If the reference temperature has been exceeded this step is by-passed.

Next, at 4, it is checked whether or not the initial over¬ shoot heating period has expired. If not, control returns to 2 and heat is again supplied for one cycle if necessary in order to maintain the temperature at the reference temperature. If the 0 period has expired control proceeds to box 5, changing the temperature reference to the normal temperature for the holding period, and the cycle repeats with this lower reference temperature.

Figure 3 shows in simplified block diagram form, the power supply, heater and controller of the invention. 5 The system draws its power from a power supply 10 which, in general, will be the normal domestic mains supply at 220/240 volts and 50/60 Hz frequency. The controller controls supply of this power to a heating element 11 by means of a triac 12. A thermostatic cut out 13 protects the equipment against overheating due to 20 accidental failure of any component.

The system operates under the control of a microprocessor 14 controlling the triac 12 through a gated buffer 15. A zero- crossing detector 16 detects the voltage zeros of the supply and supplies a gating signal to the buffer 15, ensuring that the triac 25 12 is always triggered at a voltage zero, thereby avoiding radio inter erence.

The temperature in the press is sensed by a temperature sensor 17 and compared with the appropriate reference temperature by a comparator 18. Operator switches in pre-set controls 19 allow the 30 required temperatures and times to be pre-set into the system.

A further zero-crossing detector 20 provides a signal slightly in advance of each voltage zero of the power supply to the micro¬ processor 14 and to a multiplexer 21. The multiplexer 21 switches in each cycle, so that during the positive half cycle it supplies 35 signals from the control switches 19 to the microprocessor

14 and during the negative half cycle it supplies signals from the

temperature comparator 18 to the microprocessor. The micro¬ processor operates on these signals to determine whether or not the power should be supplied to the heater in the next succeeding cycle of the supply, and if so it provides a switching signal to

5 the buffer 15. Since the multiplexer 21 and the microprocessor 14 are timed by the advanced zero crossing detector 20, which provides its signal just in advance of each zero-crossing point, the trigger signal is available at the buffer 15 just before the supply voltage falls to zero. At the instant of zero, the zero-crossing detector

10 16 supplies a gating signal to the buffer 15, triggering the triac at the moment when the voltage has fallen to zero, and so avoiding a voltage pulse which could cause radio interference.

Operation continues in this way, the triac 12 being triggered or not, as the case may be, on each cycle, under the control of the

15 microprocessor 14, to maintain the required time/temperature relationship. A display 22, making use of light-emitting diodes, may be used to indicate the stage in the process currently reached. The microprocessor itself and the timing display driving triac firing interrogation of the controls and the temperature comparators

20 may all be performed by a signal chip, for example, a COP 9411. Two further figures, Figs. 4A and 4B illustrate a preferred control program in flow chart form.

The Control Program

The control program monitors external conditions through its input 25 parts, acts accordingly, and displays its current state via its output parts.

Timing is taken from the mains zero crossing, being a change in logic level (corresponding to mains polarity) into the serial input

(SI) port. The logic level also indicates which, out of the switches 30 and temperature levels, is multiplexed into the port. Fixed external conditions, as to mains frequency (50/60 Hz), model type (old/new), and run mode (test/normal), are obtained from the L port bits 4,5 and 6. Output is via the L port, bit 7 controlling the triac, and L and D ports (L3 to _φ and D( ) controlling the LED display.

All timing loops include a call of a zero-crossing detection subroutine, as do all those that examine the switches and/or temperature levels, as these have to be read in from the G port, at the same time, and saved in the appropriate store. The timings which have to be carried out are.

1) Switch debounce of 0.1 second

2) Set time acceptance, 4 seconds

3) Heating period, as selected

4) High temperature period, 8 minutes

5) Pause period, 30 seconds

The fixed conditions manifest themselves in the following ways a) the 50/60 Hz frequency difference is compensated for by the least significant part (8 bits) of two and three part counts b) the old model uses only a subset of the complete facilities c) the test mode executes the heating period in 1/60 th of the normal mode time i.e. minutes become seconds.

All 4 register sets hold two part timing counts, in the 4 most significant registers; the sets are grouped into pairs, with one used for counting and the other holding the reset value. The parts which make up a timing count are 1) the least significant part (usually the frequency compensation count) is located in registers 14 and 15 of a set ii) the middle part, usually in registers 12 and 13 of the set (but 10 + 11 for the high temperature period) iii)most significant part, in 1, f. for LED's on count, and 3,0 for the pause period

Times are counted down, decrementing by 1 (for each mains cycle) the least significant part, and propagating the borrow. The carry flag is set on entry to the counting subroutine, and cleared if borrow is propagated from the least significant part. Also bits in the least significant part (register 1, 15 bits 2 or 3) are used to determine the on/off state of the LED display when it's being flashed.

The program comprises three main loops

- the idle loop which monitors the switches

- the run loop which monitors the temperature levels, fires the triac and inspects the stop/pause switch - the pause loop which monitors the resume (1 pause) switch with the LED display indicating the state of the program thus.

1) idle loop monitoring switches then all LED's off, or if in the set time acceptance period the displayed LED's flash at a fast rate 2) run loop (heating period) then the displayed LED are stead except for the last 5 minutes on the new model when the last LED is flashed at a moderate rate

3) pause loop then the displayed LED's flash at a slow rate

4) over-temperature condition is indicated by a 'running' LED display.

Only the first two loops are applicable to the old model, with a single switch to enter the run loop, a switch to select one of two possible heating periods, and a stop switch to return the program to the idle loop.

Idle Loop Initialisation

The accumulator is cleared and placed in the register addressed by the B register, this clears the LEDs on memory but only on power on reset, which has cleared the B register.

The L port is switched to input mode, and the fixed conditions read in, stored, and propagated through register set 0.

The LED display is set off, and the rest of register set 1 is cleared.

The G port is set for input, by sending all ones to it, and the L port is set for output.

The switch debounce time is set up in both reset value stores.

The idle loop is then entered and switch monitoring commences, with the following activities taking place if a switch is kept on for the debounce period.

Set Time Switch

The debounce time is changed to V _Λ second, then if the switch is kept on for the new duration, the LEDs on count is incremented and the corresponding display set up. From all LEDs off, the display goes to 2 on (minimum period of

15 minutes) then 3, 4 etc. up to all 8 on, then cycles back to 2 on (i.e. the 'running' LED display)

This sequence is achieved by removing the most significant bit of the count (clears all on ), then if the count is zero 2 is added, otherwise it's decremented by 1 before 2 is added.

Store/Recall

If the LED s on count is non-zero then the count is saved in the LEDs on memory, otherwise the contents of the memory is copied to the LEDs on count and the LED display set up accordingly.

The LEDs on count is converted to a display by clearing the number of bits, equal to the count, starting from the most significant bit of the 8 bit LED s on pattern store, also the set time acceptance period is set up.

Start/Pause If the switch is pressed during the set time acceptance period and kept on for the switch debounce period then the program enters the run loop via that loops initialisation.

Run Loop Initialisation

This involves setting up the heating period which is influenced by the fixed conditions and old model's selection switch as follows.

The interval between LED display changes (i.e. reducing the LEDs on by

1) termed the LED on period, is expressed in terms of the frequency compensation period.

Test mode: the frequency compensation period is unchanged at 1/20 sec. so the LED on period for a) the new model = 5 seconds = 100 * .05 b) the old model = 7%. seconds = 150 * .05 or _ seconds = 75 * .05

Normal mode: the frequency compensation period is changed to 2 seconds so the LED on period for a) the new model = 5 minutes = 150 * 2 b) the old model = 7 minutes = 225 * 2 or 3% minutes = 112 * 2

The run loop performs a number of tasks, within each _ mains cycle. 1) Time the heating period and update the LEDs on count.

The heating period timer is decremented by 1, and if the LED on period has expired the LEDs on count is updated as follows. If the LEDs on count is zero then the heating period ends by 1. The LEDs on pattern is updated by shifting it left one bit position (adding it to itself) and setting the least significant bit. The LED on period is reset and the main loop resumed if the new LEDs on count is non-zero, if the count is now zero then for the old model, control is returned to the idle loop, while for the new model it's the last five minutes, and the least significant LED is turned back on by removing the most significant bit of the OEDs on pattern, before returning to the run loop.

2) If the frequency compensation count has expired (carry bit clear) then the high temperature is decremented by 1, returning to the run loop if this has not expired, otherwise the reference temperature level is set to normal (i.e. 6) and control returned to the run loop.

3) If the stop/pause switch is not pressed then the switch debounce period is reset.

4) The current temperature level is checked and if found to be over temperature then the program goes into an endless loop, with the triac turned off. If the temperature level is found to be below the required setting then the triac is fired.

5) Finally the switch debounce is decremented by 1 and if it has not expired then the loop is repeated, otherwise control is returned to the idle loop if it's the old model, while the new model proceeds to the pause loop.

Pause Loop

After setting up thepause period time, the program'waits for the switch to be released, since it becomes themeans for resuming the run function. If the pause period expires before the switch debounce then control returns to the idle loop.