PLC - based elevator model creation
Elevator model based on PLC
Chen Qijin, Chen Cong
Zhejiang Business Vocational College (No. 1988 Airport Road, Ningbo, Zhejiang Province, 315012, China)
*This project was funded by the Zhejiang Business Vocational College Student Science and Technology Innovation Project.
Abstract This article introduces an elevator model consisting of a base, columns, control panel, and main circuit board, and demonstrates its control using a Mitsubishi PLC.
Keywords: elevator model; PLC; control flow
1. Introduction to the elevator model
The elevator model consists of a base, columns, a control panel, and a main circuit board. Five proximity switches are mounted on the columns to sense the elevator and input corresponding signals to the PLC. The car is located on the left side of the model and is controlled by a small DC motor for its upward and downward movement. The car door opening and closing signals are output from indicator lights on the control panel.
The panel has 12 input and output signals, including internal selection button signals, external selection button signals, limit signals, and door opening/closing signals. During control, each signal should be connected to the input and output terminals of the Mitsubishi PLC main unit, with the common terminal connected to the main unit's COM input/output terminal.
First, connect the model to the PLC host input and output ports. After verifying that everything is correct, turn on the power. The model will be in standby mode. Connect the computer to the PLC and input the program into the PLC. Then, start the PLC program and press the internal or external call button on the model to select a floor. If the PLC program is correctly programmed, the elevator model will run normally according to the internal or external call button instructions.
2. Introduction to Elevator Model Components
Wiring of a three-wire proximity switch: Red (brown) wire connects to the positive power supply terminal; blue wire connects to the 0V power supply terminal; yellow (black) wire is the signal wire and should be connected to the load. The other end of the load is connected as follows: For NPN type proximity switches, it should be connected to the positive power supply terminal; for PNP type proximity switches, it should be connected to the 0V power supply terminal.
The load for a proximity switch can be a signal light, a relay coil, or a digital input module of a programmable logic controller (PLC). Special attention needs to be paid to the selection of the type of three-wire proximity switch connected to the PLC digital input module. PLC digital input modules are generally divided into two categories: one type has a common input terminal of 0V power supply, with current flowing out of the input module (Japanese mode); in this case, an NPN type proximity switch must be selected. The other type has a common input terminal of positive power supply, with current flowing into the input module, i.e., a trap input (European mode); in this case, a PNP type proximity switch must be selected (as shown in Figure 1).
Figure 1 NPN type proximity switch
The elevator's small motor model is DME34B36G-108, which is a DC24V 83 RPM geared motor with an outer diameter of 34mm, a length of 37mm, a shaft length of 15mm, a shaft diameter of 6mm, a weight of 210g, and a total length of 85mm (as shown in Figure 2).
Figure 2 24V DC motor
Due to the characteristics of electronic technology, electronic devices require power supply circuits that can provide continuous and stable electrical energy to meet load requirements, and typically require stable DC power. A power supply that provides this stable DC power is a DC regulated power supply. In this project, the power supply for the 24V DC motor is a pointer-type DC regulated power supply, model DF1730SC3A. Key technical parameters: output voltage 0-30V, output current 0-3A; ripple and noise: CV≦1mVrms and CC≦5mArm; power supply effect: CV≦1*10-4+0.5mV and CC≦2*10-3+1mA; load effect: CV≦1*10-4+2mV and CC≦2*10-3+3mA; frequency meter sensitivity <100mV. Features of this DC power supply: single-channel output, with dual meters indicating output voltage and current values respectively. The voltage and current regulation modes can be automatically switched and indicated by LEDs respectively. It adopts current limiting protection and the current limiting point can be adjusted arbitrarily. The all-plastic frame has a novel and beautiful appearance (as shown in Figure 3).
Figure 3. Pointer-type DC regulated power supply
A switching power supply is a type of power supply that uses modern power electronics technology to control the on and off time ratio of switching transistors to maintain a stable output voltage. Switching power supplies are generally composed of a pulse width modulation (PWM) control IC and MOSFETs. The DR-60-24 model switching power supply is a single-phase power supply with a rated DC output voltage of 24V and a rated current of 2.5A, ranging from 0-2.5A, and a rated power of 60W. The input voltage range is 88-264VAC or 124-370VDC, the frequency range is 47-63Hz, and the AC current is 1.2A/115VAC or 36A/230VAC (as shown in Figure 4).
Figure 4 Switching power supply
3. Input/Output Allocation Table
The input signals are: 5 car leveling signals, 4 external call signals, and 3 internal call signals, for a total of 12.
The output signals include: 2 for car up/down movement, 3 for the car's current floor display, and 2 for elevator door open/close, totaling 7 signals. The input/output allocation for this project is shown in Table 1.
Table 1 Input/Output Allocation Table
enter | Output | ||
0 | Level 1 limit switch X0 | 0 | Elevator going up Y0 |
1 | 2-layer limit switch X1 | 1 | Elevator down Y1 |
2 | 3-layer limit switches X2 | 2 | 3rd floor indicator Y4 |
3 | 4-layer limit switches X3 | 3 | 2nd floor indicator Y5 |
4 | 5-layer limit switches X4 | 4 | Floor indicator Y6 |
5 | 3rd floor outbound call X5 | 5 | Elevator door closing indicator Y7 |
6 | 2nd floor outbound call X6 | 6 | Elevator door opening indicator Y10 |
7 | 2nd floor outbound call X7 | ||
8 | 1st floor outbound call X10 | ||
9 | 3-layer internal call X11 | ||
10 | 2-layer internal call X12 | ||
11 | 1st floor internal call X13 | ||
4. PLC Wiring Diagram
X0-X13 are input signals, and Y0-Y10 are output signals. COM1, COM2, and COM3 are connected to a 24V power supply, while Y0-Y10 are connected to a 0V power supply. In addition, the elevator's small motor is connected to both 0V and 24V power supplies, and the L and N terminals of the PLC are connected to a 220V 50Hz AC power supply (as shown in Figure 5).
Figure 5 PLC input/output wiring diagram
5. Software design for the elevator model
Programming logic: Taking the upward call from the 1st floor as an example, pressing button X10 activates and holds M0. At this time, Y0 is energized, and the elevator ascends. Inside the elevator, selecting a floor, such as pressing button X12, energizes and sets M12. When the elevator reaches the 2nd floor, the 2nd floor limit switch is also energized. At this point, M12 de-energizes and resets, Y0 also de-energizes, and the elevator stops at the 2nd floor. The elevator door opening indicator Y10 illuminates; after 50 seconds, Y10 goes out, and the elevator door closing indicator Y11 illuminates. Additionally, when the elevator reaches the 2nd floor, X1 is energized, and the floor indicator Y5 illuminates. The specific elevator PLC program is shown in Figure 6.
Program testing steps:
(1) When the elevator is stationary on the 1st floor, press the external up button on the 1st floor. The elevator door open indicator light will illuminate. After the door closes, press the internal button on the 3rd floor. The elevator will then ascend.
(2) When the elevator stops on the 3rd floor, the elevator door open indicator light will illuminate, and the door close indicator light will illuminate after 50 seconds. Press the up or down button on the outside of the 2nd floor to move the elevator up or down.
(3) When the elevator stops at a designated floor, the corresponding floor indicator light will illuminate.
Figure 6 PLC Program
6. Conclusion
The first key issue to address in designing a typical elevator control PLC application system is the functional design of the PLC application system. This involves defining the necessary tasks and required conditions of the system based on the functional and technological requirements of the controlled object (elevator model). The second issue is the functional analysis of the PLC application system. This involves analyzing the system's functions to determine the PLC control system's structure, the types and quantities of control signals, and the system's scale and layout. The third issue is determining the specific PLC model and system configuration based on the system analysis.
