Fisher&paykel intuitive dryer working principle

Electronic Control
The 220/240V power supply is connected to the motor control module, which rectifies to DC for use by its own controller and peripherals, and also for the sensor and display module. The motor control module has an optically isolated serial communications port to the sensor module from which it receives commands for operating the drum motor and the heater(s). The motor control module does the actual control of those devices.  The sensor module is responsible for the overall control of the dryer, including the input and output of all other peripherals. The sensor module controls the lid lock and the drum door actuator, senses the drum position and speed, measures the exhaust duct temperature through the exhaust sensor and measures the dampness of the clothes load via the sensor bars.

The algorithm for when the heaters are turned on and off, and also for the speed and direction of the motor, is implemented within the sensor module, but the switching of the elements, and control of the motor, is done by the motor control module in response to the commands from the sensor module.  When the mains power is first applied to or restored to the sensor module, the dryer will Endeavour to continue operating from when the power was lost. If mains power was lost during a drying cycle, it will continue to dry to the same set dryness level, otherwise the machine will return to have the drum door open and the lid unlocked.  The display module incorporates push buttons and a LCD display, which acts as an interface that passes user settings to the sensor module. Once Start/Pause has been pressed animations appear on the screen demonstrating the function that is being performed, alongside these animations is ongoing information regarding the chosen drying cycle etc.

Loading
The dryer always stops with the drum door open. The user places the drying load into the drum, closes the lid, pushes the Power button, selects the required cycle and presses the Start/Pause button. The lid will lock, the drum will rotate and the door grabber will slide the drum door closed. The door grabber will then move clear of the drum.

Lid Lock Control
The IntuitiveTM dryer has a lock installed in the lid to provide added safety while the dryer is operating. It ensures that the lid cannot be opened while the drum is rotating.  A Lid lock symbol (padlock) appears in the corner of the screen when locked (it disappears when unlocked). If the lid lock symbol is flashing, the lid is in the process of being unlocked. During this stage, the lid still cannot be lifted.

The lid lock is a mechanism driven by a DC solenoid and prevents the lid being opened when the drum is rotating. If the lid lock mechanism is not engaged for any reason, including open circuit or short circuit, a “Locked” is not assumed. If unable to lock after the user has requested a start, a User Warning will be given, and a fault code will get written to memory.  The lid must be closed before the drying cycle can start. If Start/Pause is pressed with the lid open, the machine will beep and a message will appear in the display screen saying “Please close the lid and press START/PAUSE”. Once the lid has been closed and Start/Pause has been pressed, the lid-lock will be activated and the drying cycle will begin.  If the power fails, either from a power cut or having been switched off at the wall, the lid may be opened. In some circumstances the drum door may not be in the open position. When the power is restored the dryer will automatically recommence the drying cycle as long as the lid is shut.

If it is absolutely necessary to remove the load before the power is restored, follow the steps below:
1. Ensure the dryer is disconnected from the power supply.
2. Open the lid (this will already be unlocked).
3. On the left hand side of the dryer there is a thumb tab that appears when the drum is not open. Press the thumb tab and rotate the drum by hand towards the back of the machine.
4. Hold the thumb tab down until the drum door starts opening.
5. Keep rotating the drum until the door is fully open and the drum comes to a stop.
6. The clothes can now be removed.
7. Close the lid once the clothes have been removed.
8. Re-connect the power supply to the dryer.
The drum door will automatically close and the dryer will resume normal operation when power is restored.

Lint Filter
Lint laden air passes through the small holes in the outlet end of the drum (the small holes around the lint bucket). The lint removal system is directly behind these holes. As this air moves through the holes it is forced through the lint filter. The fan then sucks the air down through the duct and out the back of the dryer. The lint filter in the IntuitiveTM dryer is circular and is positioned next to the drum. When the drum rotates the lint filter rotates with it. The filter is made of very fine 200-micron mesh. All clothes dryers produce potentially flammable lint. Use of a fine mesh enables a lint filter to catch more lint from the air before it reaches the exhaust ducting. That reduces the possibility of any blockages or hazards caused by the accumulation of lint.

There is a scraper situated on the top of the lint collecting housing which the filter moves past.  Where the lint on the filter builds up, the lint begins to touch the scraper, and is automatically scraped off. Because the scraper is directly above the lint bucket it falls straight in.

The scraper helps achieve consistent airflow throughout the drying cycle by continuously removing any accumulated lint from the mesh of the filter.  The dryer user manual and lid label instruct the user to empty the lint bucket before the lint reaches the top of the transparent part of the bucket. If the lint bucket overflows due to the user not emptying it, the IntuitiveTM dryer can clear itself. The user just needs to empty the bucket and run the dryer on a cycle for approximately 20 minutes. The dryer will free all the trapped lint and will re-deposit it back into the lint bucket.

The IntuitiveTM dryer will signal a reminder to the user to empty the lint bucket after every 5 cycles. This reminder is automatically selected when the customer receives the dryer.  To turn this reminder off, scroll to Options screen 4, press the Adjust button to select Off, then press Home to save the setting.

Airflow
An intake grill at the bottom rear of the cabinet provides an entry point for the airflow through the dryer via four large louvered slots. Additional air is drawn in at the front of the cabinet under the front panel. A fan on the exhaust side of the drum draws the air over the heating elements located in a combustion chamber, through an inlet duct and into the drum.  The air exits the drum through a self-cleaning lint filter in the drum outlet duct, then passes through the fan housing and out the rear exhaust vent situated at the bottom rear of the cabinet.

Temperature Control
Auto sensing is automatically selected when the IntuitiveTM dryer is turned on. The user can select a time dry option of 20, 40 or 80 minutes through the Options menu. Auto sensing of the clothes load dryness level is achieved by touch sensors that sense the moisture content of the load. An exhaust temperature sensor is used to monitor the exhaust temperature. The controller limits the temperature to what is required for the various cycles and determines what elements are used.  An auto reset thermostat located on the heater housing also limits the heat into the dryer, but if it fails to operate, them a manually resettable thermostat also situated on the heater housing will trip at 100oC, turning off the heat to protect the clothes.

Cool Down
The dryer enters a cool down period at the end of the cycle. During this period the dryer continues to run with the heating elements/burner turned off, blowing ambient air through the load to help prevent creasing.
Autosensing: If any Auto Sensing cycle has been selected, the cool down period will continue until the exhaust temperature drops to 35oC. However if this temperature is not achieved after 10 minutes, the cycle will stop. This would occur if the ambient temperature was above 35 oC.
Timed Dry: If an 80 minute or 40 minute Timed Dry cycle has been selected, the cool down period will run for the last 10 minutes of that cycle. If a 20 minutes Timed Dry cycle has been selected, the cool down period will run for the last 5 minutes.

Drum Parts.
1. Drum Inlet End: Allows inlet air to pass through. This is how air enters the drum. It also houses the inlet central bearing assembly, about which the drum rotates.
2. Drum End Outlet: Provides the route for air to exit the drum as well as securing the lint filter. The outer face has dimples, which are collectively referred to as “the drum tachometer”. The central flange of the drum end outlet is supported and guided by seven bearing pads, which are mounted in the outlet duct.
3. Vanes: Encourage clothes to tumble during the drying cycle.
4. Drum Door: Slides back along grooves in the bridge to provide access into the drum.
5. Door Bracket: Secures and seals the drum in the closed position and houses components for latching the door.

6. Hinge Arm: Part of the door assembly, which is contacted by the door grabber for opening and closing the door. It also latches the door closed over the end of the track.
7. Locking Bar: Attached to its ends are the hinge arms. Its function is to hold these hinges in the correct orientation.
8. Hinge Spring: Springs the hinge arm down to ensure latching when the door is closed.

There is also a Drum Door Scraper that prevents clothes from being drawn into the gap between the drum and the door when the door is opening, and a Key Bracket that prevents the door from closing when the clothes are protruding.

Drum Control.
The drum is coupled to a three phase induction motor by way of a pulley on the motor shaft, which drives via a “V” belt and belt tensioner system. The motor control module controls the motor by generating the three phases from a high voltage rectified DC rail. When tumble drying, the drum is tumbled at 47 RPM, during opening and closing at 5 RPM, and at other speeds as required and requested from the sensor module. Feedback on speed is via the drum tachometer signal, which comes via the sensor module.
When drying, the drum rotates in the door closing direction for 4 minutes, after which it coasts to stop and reverses for 40 seconds, then coasts to stop before repeating the reversing throughout the drying and cooling cycle. The reversing of the drum direction reduces tangling.

When creaseables is selected, at the end of the cycle the heaters are switched off, the drum then rotates in one direction for 30 seconds, then stops for 5 minutes without opening the drum door. Then it goes in the opposite direction for 30 seconds, then pauses again before turning off. If the user does not remove the clothes load, the cycle is repeated 255 times, which take approximately 23 hours.  The drum tachometer uses pressed “dimples”, formed directly into the drum end outlet, spaced every 2 degrees to provide positioning information while also providing speed data. There is a 15 degree “gap” to provide the reference for absolute position. An infrared diode and optical receiving transistor provide the reading of the “dimples.” The digital signal is output to the motor control module, which uses the signal for speed controlling the drum. The drum position is monitored by the sensor module, which uses the position for both speed commands and drum door actuator control.

Drum Door Control
The drum door is opened and closed by the door grabber, which is positioned by an actuator driven by a small DC brush motor.  A mechanical interlock prohibits the drum door from latching closed if garments get caught in the door opening. With the door unable to close, the drum will stall, which will be sensed by the motor control module and corrective action will occur. After Start/Pause is pressed when the dryer is waiting with the drum door open:
1. The lid will lock.
2. The sensor module assumes the drum door is open at “Home” and rotates the drum at 5 RPM in the drum door close direction. If it is “Home” and the grabber lowered, the door will close at 78 degrees away from “Home”. Note: If the door is closed and the grabber lowered, the drum will simply rotate with a slight rubbing noise of the grabber on the drum.

3. If the motor stalls after the drum has moved at least 42 degrees, a “Clothes Jammed” fault will be internally flagged and the drum will reverse and the door will open before trying to close again. After three unsuccessful attempts, the drum door will open, the lid will be unlocked and the relevant User Warning will occur.
4. At the “Retract Grabber Position”, 142 degrees from “Home”, the sensor module begins moving away the grabber.
• If a fault is detected during the actuator movement, the operation of the actuator will be checked. The drum will stop and an attempt will be made at moving the actuator back to lower the door grabber.
• If a fault is again detected, a maximum of five attempts are made at moving the grabber, alternating the direction with each attempt, until finally the dryer will display the relevant fault code and remain in the stationary position with the lid unlocked. If however the actuator is operated correctly, the grabber is left in the retracted position. 

5. When the grabber is confirmed to have retracted, the drum is sped up to 47 RPM and the sensor module will begin or continue the normal drying operation.

When Pause is pressed or the drying is completed:
1. If the drum is rotating in the Close direction, then it will be reversed and the drum speed will be set at 20 RPM, at which speed the position of the drum is verified using the tacho “Gap” as its reference. If however the drum was moving in the open direction, its position may have already being verified at the higher speed, but if not, will be set to slow down to 20 RPM until the position is verified. If within 40 seconds the sensor module is unable to verify its position, either because no “Gap” of sufficient arc has been detected or a correct count for a complete revolution of the drum cannot be obtained, then a fault code will be displayed.
2. Once the position is known, the drum speed begins to slow to 5 RPM. Provided the drum speed has reduced to at least 18 RPM when the drum position is 132 degrees from the extended door grabber position (210 degrees from “Home”), the lowering of the grabber begins.

3. As the bridges approach the lowered door grabber, wings on each side of the grabber enter the bridge channels. If the wings do not enter the channels, the grabber will be unable to open the drum door. As the drum continues to rotate, the engagement ribs attached to the door grabber unlatch the drum door hinge arms, lifting them out of the channel slots. The hinge arms are raised by details on the door grabber to the top face of the bridge channels. The drum continues to rotate in the opening direction, while the drum door is held stationary by the door grabber.

As the drum reaches the fully opened position, details on the drum bridges hit the door grabber, causing the motor to stall and the drum to stop. The drum is now in a fully opened position, where the user can load or unload garments from the dryer.  The dryer electronics can determine whether the drum has reached the correct position by way of the optical sensor attached to the Sensor board, which uses the dimples on the drum end outlet to determine the drum position.
4. Provided there is no failure in extending the grabber, the drum door will be opened. However, if a failure is detected in the actuator’s movement, the drum will immediately stop. The dryer will then attempt to retract the grabber. If the grabber is successfully retracted, the sequence will repeat from step 1 of this opening sequence. However, if the actuator fails to successfully move the grabber after repeated attempts, the sensor module will stop the drum in its closed state and a fault code will be displayed. Five attempts are made to open the drum door before flagging the fault.
5. The lid lock will be released.

When the power is first switched on or restored after interruption:
In normal circumstances where the previous cycle was completed successfully, when power is reapplied to the product, the sensor module will assume the door is open and the machine is at rest. In all other cases it will either continue operating or return to the “home” position so that the drum door is open and the lid is unlocked. If for some reason the drum door is not open, then the operator will need to first start, then pause the machine to return it to its drum open position. When the dryer recommences operation, the sensor module must allow for the situation where the drum door may be part way through an opening or closing sequence. In order to do this without the risk of damaging any of the mechanical parts, the sensor module executes the following sequence:
1. Moves the drum in the open direction to check if the user has manually opened the drum door, and if found so, will stop and assume the normal off position.
2. If not “Home”, moves the drum so as to close the door, moving as far as would normally be required to close the door from the “Home” (fully open) position.

3. The sensor module then operates the grabber and leaves it in the retracted position.
4. Provided the grabber was successfully retracted, the drum will continue rotating in the Close direction; ramp up to full speed, and the dryer will continue its cycle.

Heater Control.
The heaters are controlled in response to the selected drying cycle chosen and also according to other operational requirements such as reversing and overheating.  The heater housing is fitted with two elements that supply approximately 5 kW of heat when both are on. There is a 3.6kW and a 1.4kW element that are used at various times depending on the cycle chosen and the drum/fan direction.
When drying, the heater is only switched on when the drum is up to speed. Because of the time it takes for the element to cool down after switching off, the larger element in the electric model is switched off a few seconds before stopping to reverse, to prevent excessive heat entering the drum.

The software in the motor control module responds to the switching on and off of the heater as requested by the sensor module. It also monitors the automatic thermostat on the heater housing for excessive restriction of airflow, and if detected, will set a User Warning but continue the drying cycle until the end of the cycle when the warning will reset. If the User Warning occurs, the drying will take a longer time to complete and the load will possibly end up a little damp.  Each cycle has a temperature limit, as measured in the exhaust air. After switching off at the limit, the temperature has a hysteresis of 5 degrees below these temperatures when the heat source switches back on.
Note: During heating, if the temperature exceeds the limits for the particular cycle, the heat is turned off and can significantly reduce the heating time.
Cycle times can be affected by a number of factors including:
• The cycle chosen
• Load size
• Size of items
• Type of fabric
• Load wetness
• Venting method
• Location of dryer
• Condition of exhaust ducts
• Environmental conditions (temperature, humidity, etc)