Design of the Control System for the ATM Bill picking Module

 

Let's take a look at the cash machine we usually use.
Preface http://topdzh.byethost4.com/thread-383-1-1.html
The core component of the ATM is the banknote picking module, which is an automation device integrating electronics and machinery. Up to now, only a few developed countries can develop and manufacture it, however, with the improvement of China's mechanical manufacturing and automatic control technology, it is fully capable of developing an ATM Bill-issuing module suitable for China's national conditions.
　 　
Structure of ATM banknote picking Module
The ATM banknote picking module is generally composed of two functional modules: the upper layer is the banknote checking, delivery, and recycling module; the lower layer is the banknote box and coin digging module (from 1 ~ 4 banknote units with the same structure), as shown in structure 1.

The Banknote inspection and money delivery module detects the height, thickness, and inclination of each banknote dug by the banknote supply module, and sends unqualified banknote to the waste cash box by controlling the sorter, A qualified banknote is sent to the banknote follower. Finally, the banknote delivery manipulator sends the whole pile of banknotes to the banknote exit to complete a banknote export operation. If the customer does not withdraw money upon timeout, withdraw the money and put it in the cash box.

The function of the coin-picking module is to place a cash box and dig the money from one of the cash boxes according to the instructions. There are two ways to dig the money: Vacuum money suction and friction. The two methods have their own merits. Vacuum banknote suction is accurate, reliable, and easy to maintain, but the banknote picking speed is slow (1 ~ 2 sheets/second), currently only used by NCR companies. The advantage of the rubbing technology is that it is fast (5 ~ 7 sheets/second), used by most ATM manufacturers.

Figure 1 Structure of ATM banknote picking Module


Hardware Design of ATM banknote picking module control system
The main function of the entire control system is to drive solenoid valves, single and bidirectional motors, and stepper motors through various electronic circuits to realize the action of all the mechanical components of the entire banknote module, and DC voltage signals of various switch types (such as Photoelectric Sensors, micro switches, high and low voltage equal) and various physical parameters Measuring Circuits (such as the thickness of individual and whole stacks of banknotes) perform real-time and continuous checks and adjust the actions of mechanical parts in a timely manner based on the test results to ensure the correct, safe, and stable operation of the customer during the bill taking process. At the same time, when a fault occurs during operation, the fault status can be recorded, error code is provided, and corresponding fault handling can be performed to provide accurate reference data for maintenance personnel. The hardware structure 2 of the control system is shown in.

Figure 2 hardware structure of the Control System

About msc1210y5 Single Chip Microcomputer
Msc1210y5pagt is an integrated digital/analog mixed-signal microcontroller produced by TI. It features fast operation and low power consumption. Its clock frequency can reach 33 MHz and the running speed is as high as 825 MIPS, with strong data processing capabilities, the chip integrates a large number of analog and digital Peripheral modules: contains 32 KB Flash program memory, and has multiple lock functions, with strong confidentiality. In the aspect of Flash program memory programming, you can use the SPI serial interface or a general programmer to re-program, so you can program the system consisting of msc1210y5, it brings great convenience to the development of new products, upgrade and maintenance of old products. The single-chip microcomputer also contains 8-channel analog signal input, 1 ~ The 128-fold Programmable Gain Amplifier and 24-bit high-precision A/D converter are ideal for processing analog signals such as banknote thickness detection.

Banknote thickness Signal Acquisition Circuit
The system uses the eddy current sensor to collect the thickness of banknotes. the eddy current sensor can measure the distance between the tested metal conductor surface and the probe surface statically and dynamically without contact, high linearity and high resolution, the position signal is converted into a analog voltage signal, and then converted through the 24-bit high-precision ADC inside the CPU, the detection accuracy can reach 0.0005.

CPLD Circuit
In order to simplify the hardware circuit structure, improve the integration and reliability of the system, and reduce the processor burden in the application system, a stepper motor control circuit based on CPLD is adopted, the processor interface logic, stepper motor speed and Rotation Angle Control, annular pulse distributor, and chopper Constant Current Driving logic are implemented in a single CPLD device to realize the timing control of the system's banknote mining. Step Motor control logic 3 is shown.

Figure 3 logic diagram of stepper motor control

Communication and online programming Circuits
The bill issuing module and the host communication interface using RS-232C interface, through the CPU serial port 0 to achieve communication, interface chip using max3232. The online programming of MCU and communication circuit share the serial port 0 of CPU. The two use jumpers to convert interfaces. During online programming, the PC generates the RST signal, RST signal is converted to TTL level signal by max3232 to MCU programming signal psen. After MCU reset, it starts to receive the Downloaded Program.

Keyboard and display circuit
The main function of the keyboard and display circuit is that when there is no external host, the maintenance personnel can also perform operations on the banknote module, and enter the corresponding commands through the keyboard, the execution result is displayed on the LED. The LED display adopts static mode and is implemented through serial ports of CPU and serial shift of 74ls164, which greatly saves CPU resources.

Figure 4 main control system software flowchart

Banknote picking module control system software design

Banknote picking module control system software structure

The Banknote picking module control software mainly receives control commands from the ATM host, executes corresponding function operations based on these commands, and sends the execution results back to the ATM host, therefore, the control software of the ATM Bill picking module can be divided into the communication module and command function module. The communication module exchanges information between the ATM Bill picking module and the ATM host, the command module mainly provides command for bitcoin digging, command for sending cash, command for uncollecting cash, command for clearing and resetting channels, command for obtaining cash box information, command for picking and rejecting currency at the exit. operation, the ATM host sends these commands to enable the customer to withdraw money from the ATM. The entire control system software main program 4 is shown.

Communication Module

The communication of the banknote picking module is interrupted. After the CPU receives a command package, it sets up a flag. After detecting the flag, the main program reads the command package.

After executing the command, the module returns the command execution result to the PC host in a certain format. During the command execution, the module does not receive the command until the command is returned.

Command Module

The command module provides Command commands for currency digging, currency sending, unclaimed and recycled, channel clearing and resetting, command for obtaining cash box information, command for detecting currency picking at the currency exit, and command for rejecting the command.. When the ATM host software is started, you must first send the channel cleaning and reset commands to detect the status of the banknote module; for a complete withdrawal operation, the command for obtaining the banknote box information, the command for digging the money, the command for sending the money, and the command for picking the money at the exit must be sent in sequence; if the banknote is not removed within the specified time, the unclaimed banknote recycling command is sent to recycle the banknote. The command is rejected when an error occurs when the command is executed. Each command must be sent in this order. Otherwise, the command is considered invalid and will not be executed.

1-channel cleanup and reset commands

The main function of this command is to reset the internal registers of the banknote module, clear the banknote channel, and send the banknote channel. If any residual banknote is in the channel, it is sent to the recycle bin, check whether all components are normal. When the ATM host software is started, you must first send this command to clear and reset the exit module. The exit module returns the corresponding execution results to the Control Host, if the banknote module returns a fault code, it indicates that the banknote module is not working properly. The ATM Host Control Software must stop the withdrawal function and provide a fault prompt for maintenance.

2. Command for obtaining banknote Box Information

The main function of this command is to return the configuration information of the banknote box in the module, including the denomination and currency information of each banknote box, to the host control software, the Host Control software uses this information to allocate the number of banknotes in each cash box.

3. banknote mining command

The function of this command is to execute the Host Control Software to control the number of banknotes in each cash box. When the money box in each channel is dug, it must be checked, if there is an unqualified size or thickness, open the sorter to send it to the waste bin, and send the qualified banknotes to the stacking board, after the command is executed, return the number of banknotes and the number of billable banknotes in each cash box to the host, and wait for the Host Control Software to send the next command, that is, the bill sending command.

4. Bill delivery command

The main function of this command is to send the banknotes on the stacked banknote board to the gate, and the cashier can take the banknotes away.

5 banknote exit detection commands

The main function of this command is to check whether the money at the gate is taken away and return the information to the host. If the money has been taken away, the manipulator will return to the original position.

6. Unclaimed banknote recycling command

If the bank does not take the money at the gate (generally 30 seconds, controlled by the Host Control Software) within the prescribed time, the host control software will send this command, the notice module recycles the banknote at the gate and sends it to the recycle bin.

7. Command rejection

If a fault occurs during the command execution, the whole command is not successfully executed, or the command is successfully executed, but for some reason, the command cannot be sent, in this case, the host control software needs to send a denial command to notify the banknote module to send the banknote on the stack to the recycle bin.

Conclusion
Due to space limitations, this article only gives a brief introduction to the entire control system starting from the functions of the banknote picking module control system. The Banknote picking module control system introduced in this article has been applied to ATM machines. Practice has proved that the system is reliable and stable.
References
1. Edited by Deng Hongbin. Principles and Applications of msc121x system-level single-chip microcomputer. Beijing: Machinery Industry Press, 2004
2. Ike Wu et al translation. C program design of embedded systems. Mechanical Industry Press, 2002