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    The double-motor control method  for electric adjustable standing desk


    1. Brief description of electric standing desk

    In 2003, the World Health Organization pointed out that more than 2 million people die from sitting for a long time every year in the world. In 2020, 70% of the diseases will be caused by sitting for too long. Therefore, sitting for a long time is listed as the ten most deadly and disease-causing killers.Preventing sedentary life is becoming more and more important. The electric lifting desk is convenient for people to change from sitting to standing office because of its electric lifting, which can not only effectively improve work efficiency, but also help people prevent diseases caused by long-term sitting such as cervical spine and lumbar spine. It helps people say goodbye to sedentary office and study, and is gradually recognized and widely used in China.

    Power Motor has 3 electric adjustable standing motor platforms: 60/70/80KG. The 60/80kg platform is a DC motor + worm gearbox, which can bear 60/80KG on a single leg and is self-locking and reliable. It can store and remember the lifting height and realize a variety of operation modes. The 70KG platform is DC motor + multi-stage planetary gear direct push, compact structure, can be directly installed in the desk leg, single leg can bear 70KG and reliable self-locking. we own the complete patent of the planetary direct push motor, and has the advantage of technological precipitation. 



    2. Electric control function structure of electric adjustable standing desk

    The electric control part of the electric lifting table is mainly composed of two parts: the user control handle and the motor drive.

    The user adjusts the lifting and lowering of the desktop by controlling the up and down function buttons on the handle. The MCU in the handle detects the trigger of the button function, and tells the motor drive MCU through data transmission. The motor drive MCU lifts up and down according to the instruction requirements and runs to the designated position. The control structure diagram is as follows


    Flow-chart-of-control-structure.jpg


    3. Electric control drive logic of electric adjustable standing desk

    (1) UI control board control logic

    The functions of the UI control panel mainly include key control and LED display. Users can press different keys to achieve different functions, including zero return, position memory and position recovery functions, electric up, electric down and other functions. The LED display is to display the operation mode, set parameters, display height and abnormal alarm reminders through the control buttons. The operation logic is as follows:


    Flow-chart-of-electronic-control-operation-logic.jpg


    (2) Electric motor driver board control logic

    The motor driver board part is based on the instructions issued by the UI board, and performs corresponding actions according to the instructions, such as memory position, recovery position, zero return, desktop up, desktop down and other functions, the most important of which is the stable control of the motor.

    The electric lifting table uses a brushed motor to push the tabletop up and down, and controls the forward and reverse rotation of the brushed motor through the H-bridge circuit. As shown in the figure below, in figure (a), turn on Q1 and Q4, and the motor runs clockwise. If Q3 and Q2 are turned on, as shown in figure (b), the motor runs counterclockwise. In this way, the forward and reverse rotation of the motor can be controlled. In order to achieve the lifting function of the desktop.


    H-bridge-driving-principle.jpg


    In order to ensure the level of the desktop, we add a magnetic encoder to the running end of the motor, so that we can clearly know the number of turns of the motor, so that we can understand the distance of the desktop rising or falling. There is a situation where the motor loads on both sides are different. If the same voltage is driven, the running speed of the large load will be slow, and the running speed of the small load will be fast, and the desktop will not be level. In order to ensure the level of the desktop, we have adopted an effective height control algorithm, the control method is as follows.


    Flow-chart-of-height-control-algorithm.jpg


    General speaking, first of all, according to the target height and the current motor height, we can clearly know the height difference with the target height. Through the height difference, we can output the driving voltage according to the position control algorithm. The greater the height difference, the higher the driving voltage. The larger the duty cycle, the smaller the position difference, and the smaller the duty cycle of our drive voltage. In this process, different load speeds will occur. In order to maintain balance, we compensate according to the height difference of the motor, so that the speed of running fast is slowed down, and the speed of slow running is accelerated, and an effective dynamic Adjustments to balance the desktop as a whole.



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