Supervisors: Mr.K.Rotter/ Mr.S.Mondal Author: Mr.P.Adams

Transcription

1 PLC Application Exercise 7 Four Floor Elevator 1. Aim You will develop your problem solving skills by programming a real life engineering problem. This application exercise will bring together what you have learnt from lectures and lab simulations and allow you to use this knowledge to program a four floor elevator. 2. Introduction The motorised elevator can be controlled to move between four floors in response to requests from pushbuttons at each floor and inside the elevator (Side panel of elevator). The car door is motorised so on arrival at each floor it can be opened to allow passengers to enter/leave. Logic sensors are located on each floor to indicate the presence of the elevator. The elevator is controlled by a Programmable Logic Controller (PLC) located on the back panel, connected to the PC via a RS232 serial interface. 16 inputs and 16 outputs are used to control the elevator; details of these connections and function are included in the appendix.

2 3. Technical Detail The elevator car is raised and lowered by a dc motor via a 200:1 gearbox which is coupled to a toothed drive sprocket. One end of the toothed drive belt is connected to the car and the other end is connected to a counterbalance weight. The elevator car door is motorised and can be operated using the door control signal input. Taking this input high opens the door. Micro-switches detect the door status and door open/closed signals are made available for the external controller. Visual indication of the position of the elevator car as it arrives at each floor is provided by LEDs on the front panel. These LEDs are driven automatically by the internal controller. Front panel LEDs in the shape of arrows are provided to indicate the direction of travel of the car. These LEDs must be driven by the external controller. Elevator call pushbuttons are provided for each floor with separate up/down push buttons for floor 2 and floor 3. This enables the external controller to differentiate between requests for upward or downward travel and allows more sophisticated algorithms to be implemented. A separate set of floor request pushbuttons is provided on the front panel to represent the request pushbuttons inside the car. The elevator is designed so that it can be controlled using only logic signals. In this case, the car movement can be controlled using a subset of four logic inputs: 60% speed, 30% speed, direction and brake release. 60% is used for full speed and 30% when approaching a floor. A manual control is provided on the front panel which allows the car to be manually driven up and down at 60% speed. This is particularly useful during testing and debugging as it allows the car to activate all the floor sensors in turn to check that they are being read correctly by the controller. The elevator is connected to the Programmable Logic Controller via a set of contacts on the rear panel. The PLC is housed in a case on the rear panel, with connections to the elevator and PC. Here is a summary of input/output pins on the PLC and the associated functions on the elevator. PLC Function PLC Function Input Output 1 Floor 1 UP 1 Brake (HIGH is OFF) 2 Floor 2 UP 2 Door (HIGH is OPEN) 3 Floor 2 DOWN 3 UP direction Arrow 4 Floor 3 UP 4 DOWN direction Arrow 5 Floor 3 DOWN 5 Not used 6 Floor 4 DOWN 6 Not used 7 Floor 1 Call Panel 7 Not used 8 Floor 2 Call Panel 8 Not used 9 Floor 3 Call Panel 9 Floor 1 Pushbutton LEDs 10 Floor 4 Call Panel 10 Floor 2 Pushbutton LEDs 11 Floor 1 Car Sensor 11 Floor 3 Pushbutton LEDs 12 Floor 2 Car Sensor 12 Floor 4 Pushbutton LEDs 13 Floor 3 Car Sensor 13 60% Speed 14 Floor 4 Car Sensor 14 30% Speed 15 Door open 15 Direction ( HIGH is UP) 16 Door closed 16 Sounder

3 3.1 Floor Level Sensors It is very important to understand how the floor level sensors operate. At each level, there is an optical sensor comprised of a light source and sensor placed opposite each other with a small gap in between. Normally the light shines directly on the sensor and this is indicated by a HIGH logic signal. On the bottom of the elevator car is a metal bar with a number of notches, which passes through the beam as the car approaches a level. These notches block the path of the light, indicated by a LOW logic signal. There is one transition to indicate approaching level and one to indicate the car as at the level. HIGH Light Source Sensor LOW 4. Objectives To understand how to implement a simple two level elevator system To learn how a PLC can be used to make calls to Custom functions 5. Two level Elevator Two level (first and top), level pushbuttons. The elevator goes to the bottom level and waits until either the level four car pushbutton is pressed or the level four elevator call pushbutton is pressed. The elevator travels to the top floor and waits until either the level one car pushbutton is pressed or the level one elevator call pushbutton is pressed. The program is repeated. 5.1 Operation of a two level elevator There are two methods that can be used to produce a working ladder logic program. The first is to use flow diagrams, which show the operation of the elevator as a number of sequential logical operations. The second is to use a state diagram, which shows the operation of the elevator as a number of sequential or looping states. It is best to start with a written description of the system before drawing a flow diagram. This breaks the task down in to a sequence of logical events, which can then be grouped together to form a state diagram.

4 State 1 Initialisation (for two level elevators) Close doors and disengage brake Select level 1 State 2 - Wait for request Poll for pushbutton request Ignore further requests State 3 - Depart floor Close door Set direction & arrow LEDs Release brake Set motor to 60% State 4 - Approaching floor Approaching floor Set motor to 30% State 5 - Arrive at floor Turn off motor Apply brake Clear arrow LEDs Trigger sounder Open door 5.2 Method Before you start, double click TLserver located on the desktop; this initialises communications to the PLC. To start a new program, double click i-trilogi located on the desktop. We suggest you split the task as follows: Familiarisation Familiarise yourself with the inputs and outputs of the elevator. Use the manual jog switch on the front panel to observe the floor indicator LEDs as the elevator car approaches a level. Open and upload the Blank template to the PLC, located in the F1616BA folder. Use online monitoring to observe and control the inputs/outputs. Programming In your logbook, draw a flow diagram showing the complete operation of the system. If it helps, draw a state diagram, using the states outlined in the theory section of this assignment. Create a new program. Setup the inputs and outputs in the I/O table, double check the names/function with the table 1. Write the ladder logic program in the same order as they appear in the list of states. Break your program down and test each state as you progress.

5 Techniques Use custom functions to change the state of an output using the CLRIO and SETIO commands. Use a number of internal relays. These relays can be latched or cleared to signify different states. (i.e. approaching a floor) Make use of the special functions ddifd, ddifu which are only trigger the output on the rising or failing edge of a signal. 6. Further work Create a program to service all four floors. Start with a simple approach that ignores further call requests. You will need to include a more sophisticated initialisation routine that returns the elevator car to the first floor; this is so the PLC knows the location of the elevator car before taking requests. The program must work out the direction of travel by comparing the current position of the elevator car with the requested floor.

6 How to transfer programs to the PLC This section describes the step by step procedure for transferring programs to the PLC. It is essential that you carry out the steps given below exactly. Ensure the PLC is connected to the power supply and switched ON Ensure the power supply of any other Rig connected to the PLC is also switched ON. Ensure that RS232 Serial cable is connected to the PLC s COM port Run the TLserver Software if it not already loaded. You will see the following window appear. Now click on the Serial Port Setup button above. The following window appears:

7 Ensure the message COM1 opened at 38400bps is displayed in the Response window. If not please call the Technician in charge to assist you. If the message confirms that the port is opened as shown above then, proceed to the next page. Click on Controller and select Program transfer to PLC. The following window is opened: Now type in 01 in the Detect ID box and click on Memorize Username & Password to clear the Tick sign. This means the PLC should not be set with a username and password. Note: you must not set a Password for any other subsequent experiment or project. Username can be ignored and left alone as samples. Therefore the window should appear as shown below before you proceed to the next step.

8 Now click OK. Click Yes to Overwrite PLC s program. The i-trilogi software will now compile the Ladder logic to machine code. If the code contains errors, then the PLC will display an error message that the compilation is not successful. You must then go back to editing and correcting your errors. If the compilation is successful, you will see the message Success! In the Compilation window shown above.

9 Now click on Start Transfer, the following window is displayed: Click on Yes to Reset PLC? The program in the PLC will Execute and read data from input ports or output data to the devices you have programmed. The status of the PLC can be monitored by the following: Click on Controller and select On-Line Monitoring. The following example window appears:

10 The status of all devices can be monitored from this window. If A/D converters are used then the Raw Data from the converters can be seen at the top of the window in ADC1-8 boxes. This concludes a successful PLC Program transfer. The same procedure is used to transfer any program to the PLC. Virtual LCD Display You may view the Virtual LCD Display to see other status data by clicking on the View button. Click View now. You will see the Virtual LCD display window: This window is used to output up to 4 lines of text to display messages or values of Global variables. It also displays, the state of the A/D converters 1 to 8,PWM outputs 1 to 8 and the data that is output the D/A channels.