SUGISAKAMASANORI

Journal of Advances in Artificial Life Robotics
Vol. 3(2); September (2022), pp. 61–65
ON LINE ISSN 2435-8061; ISSN-L 2435-8061
https://alife-robotics.org/jallr.html

Research Article

A Low-intensity Laser Control System Design
Yuhui Cheng, Fengzhi Dai
Tianjin University of Science and Technology, 300222, China

ARTICLE INFO
Article History
Received 22 November 2021
Accepted 21 April 2022
Keywords
Single chip microcomputer

ABSTRACT
Low-power laser therapy is widely used in the treatment of various diseases as a clinical adjuvant
therapy. In this paper, a multi-channel low-power laser physiotherapy equipment design scheme
is proposed. The laser exciter used in this scheme can generate laser light with a wavelength of
650±20nm. In order to realize the requirement of multi-point irradiation, the device has designed
8 laser channels, and these channels are controlled by the main control unit composed of
STM32F407ZGT6 single-chip microcomputer. The user can control the power, frequency andworking time of the laser generator only by making some simple settings on the operation unit.
In order to ensure the integrity of the treatment process, the system has designed a power-off
protection mechanism, which can automatically save the working parameters in progress..

Laser
Pulse width modulation
Power failure protection© 2022 The Author. Published by Sugisaka Masanori at ALife Robotics Corporation Ltd
This is an open access article distributed under the CC BY-NC 4.0 license(http://creativecommons.org/licenses/by-nc/4.0/).

1. Introduction

Based on the above discussion, this design is optimized
for the precise control of multiple light sources. The designof laser physiotherapy apparatus proposed in this article
can control eight laser generators to work at the same time.
As a medical auxiliary device, safety and stability arefactors that must be considered. In order to ensure thereliability of the system, an emergency stop mode and apower-off protection mechanism are designed in this paper.
If an unexpected situation occurs during the treatment, theoperator can quickly turn off the equipment to stop theoutput through the emergency stop mode, and at the sametime, in order to avoid the loss of the set parameters after
the emergency power off. When the device is powered onagain, the power-off protection mechanism willautomatically restore the device to the state before thepower-off.

As a non-invasive treatment plan, low level laser therapy
is widely used in the treatment of skin lesions, joint lesions,vascular lesions and other diseases. It acts on the humanbody by emitting a single wavelength of laser light toproduce a series of biological stimulation responses,
thereby regulating the physiological state of the humanimmune system, nervous system, blood circulation systemand tissue metabolism system. In the application
experiments in recent years, numerous treatment cases andexperimental data have shown that the program can play agood role in specific diseases[1]. This treatment has many
advantages, such as non-invasive, short treatment time andlow risk[2]. These characteristics make laser
physiotherapy technology very popular.
Low-intensity laser physiotherapy equipment has highrequirements for performance, especially the accuracy ofcontrol signals. It also requires products with good safety
and reliability. In terms of function, for different needs,
different laser sources are needed for treatment. How tocontrol multiple laser generators to work together at thesame time is a difficult point.

2. The Hardware Structure
The final control effect achieved by the laser controller isclosely related to each functional module. According to thehardware structure, the laser physiotherapy instrument canCorresponding author’s E-mail: daifz@tust.edu.cn web: www.tust.edu.cn

61be divided into the following three parts: operation unit,
control unit and working unit, which is shown in Fig 1.

Fig.1 System structure diagram

The operation unit is an important part of the system torealize human-computer interaction. The unit consists of a
10.1-inch touch screen and an emergency stop button. The
main control unit, buzzer and power module are integrated
into a PCB circuit board, and the processing of the received
signal and the output of the control signal will becompleted in this part.
The PCB board is designed to reduce circuit complexity
and improve the practicability of the device. For aqualified product, the PCB design can directly affect its
performance. The design of the PCB board is shown in
Fig.2.

Fig.3. Front and back of the DWIN screen

The screen supports RS232 and TTL two serial portmodes for communication, and its corresponding working
voltages are 12V and 5V respectively. In order to match
the working voltage of the single-chip microcomputer,
the TTL communication mechanism is adopted in thisdesign. The communication data format is 16-bit
hexadecimal characters, and the data format is shown in
Fig.4.

Fig.4. Serial communication data format

2.2. Eemergency module
The electrical safety of the equipment is considered at thebeginning of the design of this system. In addition to theoptimization of the circuit design part, the system also
designs an emergency stop mechanism for potentially
dangerous situations. Through the emergency stop button,
the operator can cut off the power supply of the power unit
in time to avoid the occurrence of unexpected situations.
In order to obtain the status information of theemergency stop button control circuit, this design connects
the ground terminal interface to the IO port of the singlechip microcomputer. The power supply line end interface
is connected to the working unit. The emergency stop
button is shown in Fig.5.

Fig.2. The designed PCB board

2.1. Capacitive touch screen
The DWIN serial capacitive touch screen is used as thedata input terminal. Its creen resolution is 1024*600
pixels, and the ideal working power supply is 12V, 1A.
The operating temperature is between -20°C and 70°C.
The DWIN capacitive touch screen is shown in Fig.3.

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Fig.5. Emergency button

2.3. Main control unit

Fig.7. Laser drive module

The main control unit includes a control chip, a power
supply circuit and a signal output interface. The control
chip model is STM32F407ZGT6. The chip adopts a 32-bit
Corte-M4 CPU with FPU, the main frequency is up to168MHZ, and it is equipped with 140 IO ports withterminal functions. The chip has 1MB of Flash memoryand 192+4KB RAM. The equipped 17 timers can wellmeet the requirement of multi-channel PWM signaloutput[3]. Other related features are as follows:• Up to 15 communication interfaces, including 6x
USARTs running at up to 11.25 Mbit/s, 3x SPI
running at up to 45 Mbit/s, 3x I²C, 2x CAN, SDIO
• Analog: two 12-bit DACs, three 12-bit ADCs
reaching 2.4 MSPS or 7.2 MSPS in interleaved mode
• Operating Voltage 2.0V ~ 3.6V.
• Operating temperature range: -40 oC ~ 105 oC.
The design of the main control chip is shown in Fig.6.

The laser is essentially a current-mode device. Whether
the laser device emits light is related to the on-off of thecurrent. The luminous intensity of the laser device is
proportional to the current intensity within the working
range of the laser. The laser drive module actually
modulates the input electrical signal and converts it into aseries of characteristics of the laser light. The laser driver
module has four interfaces, the interface 1 is the laser
output terminal, the interface 2 is the signal input terminal,
and the interfaces 3 and 4 are the power ports. By
controlling the signal input of the laser drive module, thepower and frequency of the laser output can be adjusted.
The wavelength of the laser source used in this design is650±20nm. Lasers of this wavelength can stimulate thesubcutaneous tissue of the human body through theepidermis and dermis of human tissue. Its working
parameters are as follows:• Operating temperature range: -10 oC ~ 50oC.
• Operating voltage: 10~12V• Operating current: <200mA• Laser Safety: Class IIIB
The laser generation module is shown in Fig.8.

Fig.6. STM32F407ZGT6 chip

2.4. Working unit
The working unit is composed of a laser drive module anda laser module. The laser drive module is shown in Fig.7.
Fig.8. Laser generation module63

3. System Circuit Module Design

3.2. Design of buzzer drive circuit
For an active buzzer, the only thing to do is to input thedrive level at the signal end and amplify the drive current
through a transistor to make a sound.
Through the test, the actual working time of the buzzer
is about 4.7V, and the working current is 30mA.
The schematic diagram of the buzzer drive circuit isshown in Fig.10. In the circuit, R1 and R3 play a current
limiting role, and R2 is a pull-down resistor, which canimprove the turn-off speed of the transistor.

This system adopts the STM32407ZGT6 core board,which is equipped with the smallest circuit system ofsingle-chip microcomputer and the download and debug
interface.
Therefore, when designing the circuit, only need toconsider the signal output interface circuit, voltage
conversion circuit and buzzer drive circuit. This kind ofscheme is more convenient in design, so as to realize thedesign of PCB quickly.
3.1. Voltage conversion circuit design
The voltage conversion circuit converts the 12V DC input
from the power adapter into 5V DC through the LM2596
module.
LM2596 is a switch type step-down chip, usually is a
step-down circuit with a constant voltage output. The chipsamples the output voltage value through a resistor andinputs to the chip's feedback terminal. The output voltage
can be changed by changing the resistance of the resistor.
The schematic diagram of the power circuit design isshown in Fig 9.
Formula (1) is to calculate the Vref. The value of R1 inthis circuit is fixed at 2.5KΩ, and the value of R2 isdetermined by the chip model. When the output voltage
Vo is 5V, the resistance value of R2 is 7.6KΩ, then thereference voltage Vref is 1.24V.
Vref=Vo*R1/（R1+R2）

Fig.10. Schematic diagram of the buzzer drive circuit

4. The Functional Module
The physical architecture of this system is composed of thevarious hardware modules introduced earlier, and thesemodules complete the most basic functions. As a control
system, how to design a brief and smooth softwarearchitecture is the key point for the entire system toaccomplish the set goals.
In line with the purpose of reliability and convenience,
the operation process is simplified as much as possible inthis design. After the system is powered on, the device
starts and displays the initial interface on the interactiveinterface. After confirming to enter the system, the system
has designed a buffer time of 3 seconds, and you can enter
the preparation interface after the countdown is over. In
this interface, you can view the parameters of each laser
channel set before, including power, frequency andrunning time. After confirming the setting information,(1)

Fig.9. Schematic diagram of the power circuit

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you can enter the working interface, set the parameters ofeach channel, and start the laser.
During the working period of the system, all parametersof the current operation will be saved at any time to avoid
data loss caused by unexpected situations. When theworking time of the channel reaches the set value, thesystem will prompt the operator through the buzzer andclose the corresponding laser channel at the same time.
The system work flow chart is shown in Fig.11.

When an emergency stop is needed, the emergency stop
module can also respond quickly and save data.
References
1. Moskvin SV, Agasarov LG. Laser Acupuncture: 35 Years of
Successful Application in Russia (Narrative Review).
Journal of lasers in medical sciences vol. 2020,11: pp.381389.
2. Tony Y. Chon, Molly J. Mallory, et al., Laser Acupuncture:
A Concise Review, Medical Acupuncture. 2019,6: pp.164168.
3. Cui Lin, Zhu Lei, Bai Lu. Design of PWM waveformgenerator with adjustable parameters based on STM32 (inChinese). Information and Communication, 2018, 1: pp.129131.

Authors Introduction
Mr. Yuhui Cheng
He received his Bachelor's degreefrom the Internet of Things
Engineering, Tianjin University ofScience and Technology, China in2019. He is currently studying for amaster'sdegree
inelectronic
information at Tianjin University ofScience and Technology.

Dr. Fengzhi Dai
He received an M.E. and Doctor ofEngineering (PhD) from the Beijing
Institute of Technology, China in 1998
and Oita University, Japan in 2004
respectively. His main researchinterests are artificial intelligence,pattern recognition and robotics. He
worked in National Institute ofTechnology, Matsue College, Japan from 2003 to 2009.
Since October 2009, he has been the staff in Tianjin
University of Science and Technology, China.

Fig.11. System work flow chart

5. Conclusion
Through testing, it can be concluded that this design cancomplete the work of controlling eight laser generators atthe same time. In continuous mode, four-speed power
adjustment can be achieved. In the pulse mode, the default
working time is 30 minutes, and each laser generator has aseparate timing channel, which can realize the time settingof 0-99 minutes. The default laser power is 50%, and theadjustable range of power is 0~100%. The default laser
frequency is 50Hz, and the adjustable range is 1~1K Hz.
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