Design of control system for double-head blind hole drilling machine based on PLC and touch screen

O Introduction
Double-head blind hole drilling machine is a common machine tool for drilling holes on solid materials. It is widely used in parts processing and production in industries such as molds, automobiles, and machine tool manufacturing. Traditional manual processing is not only slow, but also very easy to make mistakes, resulting in low product productivity.
Programmable logic controller (PLC) has the advantages of good stability and high control accuracy, and is often used as a controller; the addition of touch screen not only enhances the space for human-computer interaction, but also reduces the use of external I/O points of PLC and reduces the complexity of system wiring to a certain extent. The control system composed of the two is increasingly widely used in various fields of industrial production.
Here, a control system is designed using Panasonic PLC (FP-X (260T) and Weinview touch screen (Weinview MT506). The practical effect shows that it can fully meet the design requirements of double-head blind hole drilling machine.

l Process control requirements and control system composition
The mechanical diagram of the double-head blind hole drilling machine is shown in Figure 1. It is mainly composed of 6 cylinders, 4 stepper motors, and 2 spindle motors. Among them, cylinder 1 plays the role of pressing the workpiece; cylinder 2 is used for positioning, so that the tool and the processing point are on the same horizontal line; cylinder 3 plays the role of tightening the workpiece to prevent the workpiece from slipping away from the processing position due to loosening due to external force during processing; cylinder 4 is used to rotate the workpiece. When one surface is processed, the second surface needs to be processed. When the second processing is performed, the workpiece needs to be rotated once; cylinders 5 and 6 play the role of aligning the center position of the workpiece.

Four stepper motors control four axial movements respectively. The left and right moving motors move toward the processing platform, and the two left and right drilling motors equipped with the spindle motor are close to the processing platform; the left and right drilling motors are responsible for pushing the spindle motor forward for drilling processing. The spindle motor is equipped with a tool. During the processing process, if the processing is completed in one go, the coolant is difficult to enter due to the processing depth being too deep, resulting in excessive tool temperature and burnout, and iron chips are difficult to discharge, which in turn leads to processing errors, affecting the processing accuracy and production efficiency. Therefore, during the processing process, it is necessary to periodically withdraw the tool from the workpiece to be processed to play the role of chip removal and heat dissipation.
1.1 System process control requirements
The control actions of the double-head blind hole drilling machine are mainly divided into cylinder actions and motor control actions. Among them, the cylinder action completes the workpiece clamping, pushing the material into place, etc.; the motor action completes the automatic processing action of the motor. The main control requirements are:
(1) It has manual/automatic function status. When manual, it is required to independently operate each step of the cylinder action and motor action in the process to facilitate machine commissioning. When running in automatic mode, it must run strictly in accordance with the timing requirements of the process steps.
(2) The left and right drilling motors must start moving only after the left and right moving motors have completed their movements, to ensure that the tool will not hit other parts and be damaged.
(3) When drilling, the left and right drilling motors are required to move forward and backward periodically, pushing the spindle motor and the tool to complete the entire processing action, that is, one process must be divided into multiple small line segments to ensure that the tool can be withdrawn from the workpiece after each forward processing, thereby achieving the effect of chip removal and cooling.
(4) Emergency stop protection measures are required. When the emergency stop button is pressed, an alarm signal is generated, and at the same time, all parts of the machine tool stop moving, and only the return to zero operation is effective. The alarm is canceled when the return to zero operation is started.
(5) Tool changing and tool setting functions are required. When the tool is found to be unfavorable, automatic tool setting operations must be performed after the tool is changed.
1.2 System architecture

The control system adopts the combination of Panasonic PLC and Weilun touch screen: the Weilun touch screen is mainly used for setting processing parameters, sending control signals to the PLC and displaying the status information of the PLC (such as alarm information, ongoing process number information, etc.). Through touch screen software programming, the variables in the touch screen are directly mapped to the PLC, so that each action on the touch screen can be directly reflected in the PLC; the PLC reads the input signals from the field and the control signals of the touch screen, scans the program according to the pre-programmed program, and outputs the control signal to the machine tool to control the motor or cylinder action; the field sensor input signal is composed of the left and right movement motor limit position, the origin sensor and the left and right drilling motor limit position, the origin sensor and the spindle motor current sensor and other input signals.

2 Hardware Design
Considering the system process requirements, the FP-X C60T PLC produced by Panasonic was selected. The PLC has 4 pulse outputs. Since each pulse output has a pulse output port and a pulse direction output port as well as an origin position and limit position input port, it needs to occupy 4×4=16 I/O ports; according to other control requirements of the system, 4 input ports (spindle over-limit current and emergency stop, start input) and 10 output ports (including control output and alarm signals for 5 cylinders, oil pump signals, spindle motor over-current output signals, etc.) need to be set.
The touch screen uses Weinview MT506 touch screen, and its development software is Easy Builder, which is simple and easy to learn.

3 Software Design
3.1 PLC Software Design
Panasonic FP-X C60T uses FPWIN GR Ver. 2.72 software for programming design. It can be programmed in ladder diagram language and sequential function chart language. This design uses ladder diagram programming.
Software design includes manual mode and automatic mode design. The manual mode requires that each action can be run independently. When operating in automatic mode, the entire set of actions must be completed in strict accordance with the operating procedures required by the process. The software design process is shown in Figure 2.

3.1.1 Automatic mode design
The workflow of the double-head blind hole drill in automatic mode is shown in Figure 2. Since the automatic mode has strict process requirements, the step transfer instructions of Panasonic PLC are used in programming: SSTP, NSTL, NSTP, CSTP, STPE and other 5 instructions. For the control of the stepper motor, the pulse output instructions F171 (SPDH) and F172 (PLSH) in Panasonic PLC are directly used. By setting the pulse output instruction control word, the minimum speed, maximum speed, acceleration time, number of pulses, etc. of the stepper motor can also be adjusted. Using Panasonic PLC, it is very convenient to control the stepper motor.
3.1.2 Manual mode design
The manual mode is generally used in the trial operation and debugging stage. There are 6 cylinders running in single step, 4 stepper motors running in single step, and 2 spindle motors running in single step. For stepper motor control, the method of calling sub-functions is used to run each stepper motor in single step. In addition, the tool change and tool setting function also needs to be completed manually.
3.1.3 Stepper Motor Control Skills
For stepper motor control, Panasonic PLC special instructions F171 and F172 are used. Among them, there are two different controls for F171, one is ladder diagram control, and the other is origin return control. The two controls are selected by setting the data table. This instruction can be used for stepper motor control in automatic mode. For instruction 172 (PLSH), it is JOG control, which can be used for motor control in manual mode.
3.1.4 Emergency stop function design

When any fault or emergency occurs, emergency stop protection measures are required. Once the emergency stop button is pressed, the cylinder remains in its original state; for the stepper motor, its pulse output needs to be stopped so that the motor stops rotating. This can be done by setting the control command word of the pulse output. Once an emergency occurs, the emergency stop button is triggered, the pulse output instruction is turned off, the stepper motor stops, and an alarm signal is generated. When the return to zero button is pressed, the alarm signal is turned off and each stepper motor returns to the origin. At the same time, some internal data in the PLC system needs to be initialized so that the drilling machine can continue processing after the alarm signal is eliminated, instead of continuing to operate under the condition when the fault occurs.
3.2 Touch screen design
Touch screen design includes two aspects of design: creating a human-machine interface and realizing communication with the PLC host.
3.2.1 Touch screen human-machine interface design
Use Easy Builder software to design the human-machine interface. The software provides a variety of control device libraries, graphic spaces and functional components. According to the system process requirements, there are 4 interfaces including the main screen, manual 1, manual 2, manual 3 and parameter interface. Among them, the components configured in the main interface include return to zero point, tool change and tool setting buttons, manual/automatic switching buttons, spindle motor buttons, cylinder oil pump buttons, start buttons and emergency stop buttons; Manual 1 and Manual 2 are manual and separate controls for the left and right moving motors and left and right drilling motors respectively, and both are equipped with fast/slow speed switching buttons, left and right forward buttons and left and right backward buttons, simultaneous forward and simultaneous backward buttons, etc.; Manual 3 interface is a separate manual control of the 6 cylinders, and a button is assigned to each cylinder; The parameter interface mainly sets the initial position of the workpiece processing, drilling depth, feed amount and other parameters. Figure 3 is the structural diagram of the human-machine interface of the double-head blind hole drilling machine.

3.2.2 Communication between touch screen and PLC
Set the variables in the human-machine interface to establish a connection with the corresponding I/O points or storage units in the PLC, realize the control of the touch screen over the PLC and the input of parameters, and control the operating status of the PLC.
In addition, it is necessary to set the communication parameters between the touch screen and the PLC to realize the communication between the touch screen and the PLC.

4 Conclusion
In the drilling system, the use of PLC control makes the system hardware circuit design simple and reliable, and the design of the touch screen enhances the human-computer interaction capability, while also greatly reducing the use of electronic devices such as switches, buttons, indicator lights, and instruments in traditional control methods, and indirectly reducing the use of PLC external I/O points, simplifying the system hardware design. The combination of the two combines their respective advantages, is not only convenient to operate, but also more secure and reliable in system performance, and has broad application prospects.