Handwheel switch status detection system design

        Handwheel switch to low-power AC motor providing a plurality of gear.
        Main factors affecting the service life of the rotary hand wheel switch arcing ionization is the quality of materials and the contact copper appears during sliding, the fault manifested as poor contact or contact resistance. Handwheel current switch status detection research aimed at the switch or not to detect weak changes in load current, and the rotary switch is as small AC 220V AC motor circuit part, under conditions with different loads, the level is not at the time of exposure to ionizing the same, so the life of the keys are different. Because the market switch life test equipment loaded on the switching voltage of low-voltage direct current, it can not meet the test requirements of the rotary switch. Switch life depends on its mechanical failure and degree of ionization, and these two factors that affect the flow of current through the switch, they need to solve problems in real-time current sensing. Current transformers and Hall sensors can achieve detection of alternating current. Rotary switch status detection system needs to solve the problem in the case of a power switch with AC220V load, mechanical design and motion control systems and to analyze and calculate the effectiveness of the switch, to reduce the difficulty of detection and the purpose of reducing labor costs.
        1 System Architecture Design
        According to the actual demand, and the characteristics of the rotary switch, so this paper the characteristics of the test button, to design control systems and mechanical execution unit. Under the command of the control system controls the deceleration motor driven rotary gear mechanical portion of the rotating, six rotary switch while driving on hand rotary disc gear, the gear when the turntable rotates, driven switch and encoder synchronous rotation. Rotary encoder provide rotational angle signal, the feedback to the control system.
        2 Mechanical design execution unit
        Handwheel switch is a three effective and two neutral gear switch, the angle between adjacent stalls are 18 °. To improve the efficiency of the test hand wheel, designed by a gear motor driven mechanical rotary switch six execution units. Considering the slowdown in the motor torque, the torque required to rotate the rotary switch, as well as ease of installation on the basis of the design of the overall machine mechanical structure. Neutral, a gear, second gear, third gear and neutral connections, the total rotation angle of 18 ° * 4 = 72 °. Geared motors using Alogn JGB37 - 3625 brushless DC gear motor, speed 20 rpm / min, rated torque to zero. 08 Kg · m.
        When the gear motor rotation, reverse rotation drive turntable, the turntable is rotated forward rotation switch.
        3 Control System Design
        3.1 Control System Design
        Control system needs to achieve state of the peripheral input, output and control signal functions such as human-computer interaction. Handwheel system is based on the minimum system C8051F120 microcontroller is a circuit core, this SCM and reach 49 MHz internal oscillator with the PLL frequency multiplier crystal, instruction speed 100MIPS. Each rotary switch has three valid stalls, different rotational angles conduction, these three positions can be connected in parallel, sharing a channel transformer current detecting circuit, so that six channels can detect six rotary switch. The system uses input AC220V, output for the entire system to provide the main power switch DC24V and DC5V power supply, for an additional 3.7 V lithium battery backup power to the SCM system. DC24V switch battery battery drive power reduction, and to provide power to transformer current detecting circuit operational amplifier. DC5V provide power to the SCM system. Rotary encoder feedback rotation angle information. Buttons and LCD provide interactive features, providing feedback function selection and testing information for the user's hand wheel. Current detection circuit provides + 24 V and GND input pins, as well as a hand wheel and the detected current corresponding analog voltage output pin. System to detect the input voltage value of the current detection module through the microcontroller ADC. 3. 2 DC power supply circuit using the output power of 120W of DC 24V switching power supply, in order to ensure that there is enough power to drive geared motors. Relationship DC3.7 V lithium battery, DC5V power supply and microcontroller require DC 3.3 V power supply shown in Figure 4. DC5V power supply is via the AS1117 buck into three. After 3V provide power to the SCM system, DC3.7 V lithium battery after a IN4007 series as standby power microcontroller, enabling the microcontroller uninterruptible power supply. As long as the voltage DC3.3V at not less than 2.7 V microcontroller can guarantee work, keep the microcomputer inside information. Because the lithium battery provides power for the MCU only, so it can guarantee one charge more than three months of life. When the battery voltage drops 3.3 V, the voltage DC3.3V at about 2.6 to 2.7, although at this time there are still about 30 percent of the battery power, but can not effectively maintain internal microcontroller data. To monitor the battery voltage, the system will DC3.7V through 10K potentiometer partial pressure is input to a channel ADC0 in alert the operator when the detected voltage is lower than the actual requirements of the battery. 3.3 gear motor gear motor control circuit using DC24V, with IRF540N as the motor on-off control. Motor control circuit shown in Figure 5. And D8 as 1N4733. Motor and M_Dir motor off and direction of rotation of the control signal from the microcontroller, when the Motor is high, Q2 is turned on, DC24V, D5, motor, Q2 and the reference constitutes a loop. When Q2 is stopped, D5, D6 and motor constitute freewheeling, so back EMF when the motor stops to get quick relief. Motor signal is inactive, R4 ensure Q2 in the off state. And R2 with the zener diode D8 and D7 and R3 complexes, respectively MCU Motor and M_Dir pin sink current maximum limit 100 mA, play a protective role in the microcontroller.
        3. 4 encoder output circuits other hand wheel rotation have AB two-phase, open-drain output, so you need through a pullup resistor respectively connected to the microcontroller again / INT0 and / INT1 interrupt pins, the corresponding interrupt service routine by feed pulse count , and determines the direction of rotation. Current sensing transformer based Precision AC detection module, the range is 0 ~ 5 A, the output voltage is adjusted pro-rata. There are six channels, six groups of keys can simultaneously detect output current. ADC microcontroller output voltage received handwheel, sampled and analyzed by a program processing. In addition, lithium battery voltage also access ADC, so that together with the acquisition by ADC.
        4 parameter calculation
        4. 1 Initial angle calculation system uses 600 pulses / turn rotary encoders, rotary switches each file rotation angle of 18 °, geared motors and rotary encoder angle synchronized, so every rotation of a file, so the number of pulses required gear motor rotation angle corresponding Pm to 105.
        4. 2 Select the typical tungsten juicer power 150 W, 1. 2 times the rated current, Tungsten power Pw is: Pw = 150W * 1. 2 = 180 W, it should choose the closest to this power of 200 W tungsten lamp as a load.
        4. 3 to calculate the threshold current is set off the fault voltage load voltage is 10%, viscosity breakdown voltage is 80% of the load voltage. 200 W tungsten rated current I0: I0 = 200W / 220V = 0. 91A, therefore, breaking the fault threshold current Id and sticky fault threshold current In as: Id = I0 * (1 - 10%) = 0. 82 A, In = I0 * (1 - 80%) = 0. 18 A.
        4. 4 AC current measurement module of linear analysis handwheel AC current measurement modules rated range is 5 A. However, due to the system, load only 200W, to increase the dynamic range, adjust the potentiometer on the module output scaled. The amplified value is linear, linear analysis is required.  The nominal value and the actual value error due to the presence of the load, so the use of UNI - T Youlide UT203 digital clamp multimeter voltmeter measurements for comparison. Of the ideal line. Linear regression equation is: Ix = Vy / 2. 2, which is the actual current Ix, Vy as a result ADC0 measured.