ELEVATOR CONTROL SYSTEM

Transcription

1 ELEVATOR CONTROL SYSTEM Deliverable I ECSE 421 Embedded Systems McGill University Professor Brett Meyer Team RADE Ming-Yuan Chiang Riham Bichri Dmitry Rivkin Alex Varghese March 22, 2012

2 Hardware Requirements To determine our hard requirements we first must choose which type of elevator we will be using. There are two major types of elevator design: hydraulic elevators and roped elevators. The hydraulic elevator requires more energy to raise the cart and is less energy efficient. For this reason, we will use the roped elevator. Unlike the hydraulic elevator, the car is not pushed from below but rather raised and lowered by traction steel ropes. Our gearless systems will have the motor directly coupled to the sheave and thus no need for a gear train. The roped elevator will keep our cost and power requirements lower than a hydraulic elevator. The ropes are attached to the elevator and are looped around a pulley with grooves around the circumference. This rope is connected to an electric motor and it rotates the pulley to move the ropes. The ability to raise and lower the car comes from the friction of the ropes against the grooved sheaves. The ropes that lift the car are connected to a counterweight which hangs on the other side of the pulley. The purpose of this counterweight is to conserve energy due to its use of potential energy. Even though one rope can support the weight of the elevator it contains multiple ropes in case if one breaks due to safety requirements. Our elevator will have automatic braking systems near the top and the bottom of the elevator shaft. If the elevator car moves too far or fast in either direction, the brake brings it to a stop. And in case all fails there is a shock absorber at the bottom of the shaft to soften the car s landing. If the passenger presses the stop button it would trigger the emergency brake. An intercom will be placed in the elevator so that the passenger can communicate in case of emergency. The requests are controlled by microcontroller. The microcontroller s job is to process all of the information about the elevator and turn the motors. Requests are sent by the passengers pressing buttons within the elevator or individuals outside in the hall waiting to get on the car. Theses buttons are touch sensitive (tactile sensor) and have lamps which dim or brighten by touching the base.

3 We will be using a light sensor to determine position of the car. The light sensor is on the elevator. A load sensor can tell the microcontroller how full the car is. This load sensor is a safety feature. The doors on the elevator are controlled by electric motors. Basically, the electrical motor turns a wheel is attached to a metal arm attached to door sliding it back and forth on a metal rail (shown below). The doors open when the car arrives at a floor and closes before the car starts moving again. The car doors have a clutch mechanism to prevent the door from opening during motion. Our elevator will have a motion sensor system that keeps the doors from closing if somebody is between them. If the doors are held open too long on a floor an alarm system will go off or if there is no elevator response within 5 minutes. To conclude, below are the requirements for each component of the elevator: The system requests will be processed by a microcontroller. Door Door Electric Motor: To open and close the door. Locking Mechanism: To indicate that the door has been correctly closed. Motion Sensor: To detect objects preventing the door from being closed. Timers: Times how long the doors are kept open. Alarm system: It goes off it door if kept open longer than a pre-determined amount of time or if no elevator response within 5 minutes. Load sensor: Determines the capacity via current weight in elevator.

4 Shaft Emergency brake: Activates when stop button is pressed or elevator malfunctioning. Hall Tactile sensor (touch sensor): Will be the buttons representing up, down Elevator Position Display: Display the position of the elevator on each floor Elevator Elevator Electric Motor: moves the elevator up or down. Tactile sensor (touch sensor): Will be the buttons representing stop and floor number. Intercom: When communication with passengers is necessary. Light sensor: Indicate which level the elevator is at or leaving. Please note these hardware requirements are specifications for one elevator and must be included in all three elevators present in our model.

5 Software Requirements Since we will be using the standard electric gearless roped elevator model, our software requirement will depend on the hardware components of this model. Dispatcher Software: Since we have three elevators, our dispatcher software will have to use the elevator position signals to determine which elevator to send when a user calls an elevator. When priority floors signals (top floor and bottom floor) are not involved, depending on the direction of the elevator and the floor up/down request signals, the software will decide which elevator is closer to the user and send that elevator. Door Controller Software: The door controller software will have a timer, once the timer exceeds the maximum allowable value, it will send a signal to the alarm system to sound off the alarm. The software will need to take the input from the load sensor and motion sensor and send a signal to the elevator controller to close or open the door. Elevator Controller Software: By taking the signals from the dispatcher software and the buttons signals inside the elevator indicating which floors have request for the elevator, the elevator controller system determines which floors to stop on its way down/up. Since we have an automatic braking system, our safety software will take the speed of the elevator into account and output a new speed for the elevator, the same system will also respond to the STOP button signal when it is pressed to slow down and stop the elevator in the case of an emergency. Hall Button Controller Software: The hall buttons takes in up/down request signals from each floor and sends them to the dispatcher. Sensor Software: The load sensor software will implement functions that detect the load of the elevator and output a signal when the maximum weight has been exceeded. The light sensor software should refresh the floor number every time it detects a new input from the light source on each floor. The tactile sensors should output a signal every time the pressure on a button exceeds the threshold value or when an elevator reaches its destination. Lastly, when the door is open the motion sensor needs to send a true or false signal every period indicating whether an object is in the way of the door or not.

6 Implementation Metrics Requirements Software Metrics Sensor Monitoring Software: Since the safety features of the design rely on acting quickly on information from the sensors, the metric for the sensor monitoring software will be worst case execution time, and values from the sensors should be obtained every 50ms or so. Dispatcher Software: This software is not safety critical, and controls a slow mechanical system. Therefore, the relevant metric is the average execution time, which is the time between the user request and the elevator dispatch. This time can be around 500ms. The other metric of the performance of this software is the efficiency of the elevator-dispatching algorithm. Our system must minimize the power used by the elevators without making any person wait too long. Therefore, performance will be measured by the total distance traveled by the elevator and the average and maximum waiting times between a request from a user and the delivery of that user to their destination. Elevator Controller Software: The elevator controller software must constantly monitor the sensors to make sure that it is safe for the door to close or open. The execution time of this process should be no more than 200ms. (worst case). Once closing or opening is deemed safe, the door software should be able to send the signal to activate the door s motion within 300ms (average) so as to minimize transportation time for the users Automatic Braking Software: The process which reads the sensors and determines whether automatic breaking is needed or not should have a worst case execution time of no more than 100ms. Then, execution must switch the process which controls the automatic braking and the braking must begin in no more than 100ms.

7 Hardware Metrics Door The motor that actuates the door must be able to open or close the door within two seconds (average). The direction of the doors motion (i.e. opening or closing) must be reversed within 200ms. The locking mechanism must open or close in 500ms (average). The motion sensor on the door must provide updated data every 50ms (worst case) since safety features depend on it. Shaft The emergency brake in the shaft must be able to activate within 100ms of getting the command from the software. It must also be able to slow the elevator down from up to two times max normal operating speed to a stop within one second. Car/Hall The elevator motor must be able to accelerate the car at up to 3 m/s 2 up to a maximum speed of 10 m/s in order to allow for timely operation. The sensors that monitor the position and speed of the car must offer new data every 25 ms (worst case) to allow for precise control and safe operation. The microphone and speakers on the intercom must allow for clear communication between 300Hz and 3500Hz (which is the frequency range of the human voice). Processor The processor must be capable of running a real time operating system quickly enough to ensure that the requirements outlined in the software requirements document in such a manner as specified by the software metrics document. Energy use will not be an important factor since the processor will be located in a large building with a good connection to the power grid. The cost of the processor should be under $1000 CAD.

8 Use Cases For all cases, assume button pressing takes between 0.5 to 1 Second. Signals passing take between 20 to 50ms. Chart 1. The user requests the elevator from the hall. The dispatcher chooses an elevator. The elevator controller moves the elevator to the floor which called it, after it finishes other possible tasks beforehand (Eg. Dispatcher sends elevator to floor 3, elevator stops on floor 2 since a user has pressed for floor 2 beforehand). Chart 2. The user is already in the elevator and selects a floor. The elevator controller turns the light on, updates the dispatcher and display with the information, arrives at the floor and turns the button light off.

9 Chart 3. The user request the elevator from the hall, the dispatcher calls for the elevator, the elevator updates the dispatcher with its position, if the position has not changed after 5 minutes, the elevator controller sounds the alarm Chart 4. The user in the elevator selects a floor, the elevator starts moving, user then press the stop button, the elevator signals the elevator to stop

10 Chart 5. The user enters the elevator and selects a floor, the elevator controller signals the elevator to move, the elevator arrives at its destination, opens the door. The door is left open due to some obstacles, the door controller sends a signal to the elevator controller indicating the door is open for too long which result in a warning. Chart 6. The user in the hall requests for the elevator, the elevator arrives at the requested floor, the user (multiple guests) enters the elevator and exceeds the maximum allowable weight, and the door is kept open.