What Is the Difference between Stepper Motors and Controllers?

A stepper motor controller is an electronic product that can emit a uniform pulse signal. After the signal sent into the stepper motor driver, it will be converted by the driver into the strong current signal required by the stepper motor to drive the stepper motor. The stepper motor controller can accurately control the stepper motor through every angle.

1.Stepper motor drive circuit

The stepping motor drive circuit is designed based on the H-bridge circuit. The use of discrete element MOS tubes to build the dual H-bridge drive circuit is a mature motor control scheme. The circuit is not complicated and the performance is reliable. The upper limit of the working current of the MOS tube can even be as high as tens of amps. The MOS tube H-bridge driving circuit has NMOS configuration and PMOS + NMOS configuration. The full NMOS tube H-bridge on-resistance is smaller, but the on-voltage of the NMOS tube of the upper arm is higher than the power supply voltage, which requires an additional booster circuit. This increases the complexity and cost of the circuit. We use the PMOS + NMOS configuration to build a dual H-bridge stepper motor drive circuit. The circuit is simpler and the cost is lower; and in such low-current working situations, the PMOS added The conduction loss is negligible. The drive circuit is isolated from the MCU by optoelectronics. A widely used low-cost optocoupler PC817 is selected. Add dual-input four-channel AND gate (74HC08D) to add an enable function to the drive circuit, that is, the four-channel control signal is only valid under the premise of enabling, making the stepper motor run more safely and stably. IRF5305 is used for the MOS tube And IRF1205, its parameters are 55V, 110A, TO252 chip package. The schematic diagram of the stepping motor drive circuit is shown in the figure.

1. Set the number of subdivisions of the stepper driver. Generally, the higher the number of subdivisions, the higher the control resolution. However, if the number of subdivisions is too high, the maximum feed rate will be affected. Generally speaking, for mold machine users, the pulse equivalent is 0.001mm / P (at this time the maximum feed rate is 9600mm / min) or 0.0005mm / P (at this time the maximum feed rate is 4800mm / min); for accuracy requirements For low users, the pulse equivalent can be set larger, such as 0.002mm / P (at this time the maximum feed rate is 19200mm / min) or 0.005mm / P (at this time the maximum feed rate is 48000mm / min). For a two-phase stepper motor, the pulse equivalent is calculated as follows: Pulse equivalent = lead screw pitch ÷ number of subdivisions ÷ 200.

2. Take-off speed: This parameter corresponds to the take-off frequency of the stepper motor. The so-called take-off frequency is the highest frequency at which a stepping motor can start working without acceleration. Reasonable selection of this parameter can improve processing efficiency and avoid low-speed sections with poor motion characteristics of stepper motors; however, if this parameter is selected too large, it will cause stuffiness, so be sure to leave a margin. The factory parameters of the motor generally include the parameters of the take-off frequency. However, after the machine tool is assembled, the value may change, and it will generally decrease, especially when doing load movement. Therefore, it is best to set the parameter by referring to the factory parameters of the motor and then measuring it.

3. Single-axis acceleration: It is used to describe the acceleration and deceleration capacity of a single feed axis, and the unit is mm / sec square. This index is determined by the physical characteristics of the machine, such as the mass of the moving part, the torque, resistance, and cutting load of the feed motor. The larger this value is, the less time is spent in the acceleration and deceleration during the movement, and the higher the efficiency. Generally, for stepping motors, the value is between 100 and 500, and for servo motor systems, it can be set between 400 and 1200. In the setting process, start to set a little smaller, run for a period of time, repeat various typical exercises, pay attention to observation, if there is no abnormal situation, then gradually increase. If abnormal conditions are found, lower the value and leave a 50% to 100% insurance margin.

4. Curve acceleration: It is used to describe the acceleration and deceleration ability when multiple feed axes are linked. The unit is millimeter / second square. It determines the maximum speed of the machine tool when making circular motions. The larger this value is, the greater the maximum allowable speed of the machine tool during circular motion. Generally, for a machine tool consisting of a stepper motor system, the value is between 400 and 1000, and for a servo motor system, it can be set between 1000 and 5000. For heavy machines, this value is smaller. In the setting process, start to set a little smaller, run for a period of time, repeat various typical linkage movements, pay attention to observation, if there is no abnormal situation, then gradually increase. If abnormal conditions are found, lower the value and leave a 50% to 100% insurance margin.

Generally considering the driving capability of stepper motors, the friction of mechanical assembly, and the bearing capacity of mechanical parts, the maximum speed of each axis can be modified in the manufacturer's parameters to limit the maximum speed of the three axes when the machine tool user actually uses it.

5. According to the installation positions of the three axis zero point sensors, set the parameters of returning to the mechanical origin in the manufacturer parameters. When the settings are correct, you can run "Back to Machine Origin" in the "Operation" menu. Perform single axis return first. If the movement direction is correct, continue to return, otherwise stop, reset the direction of returning to the machine origin in the manufacturer parameters until all axes can return to the machine origin.

6. Set the automatic fueling parameters (set smaller, such as refueling every 5 seconds) and observe whether the automatic fueling is correct. If it is correct, set the automatic fueling parameters to the actual parameters required.

7. Verify that the settings of the electronic gear and the pulse equivalent match. You can make a mark on any axis of the machine tool, set the coordinate of this point as the working zero point in the software, use the direct input command, jog or handwheel to make the axis travel a fixed distance, and use vernier calipers to measure the actual distance Whether it is related to the coordinate display distance in the software.

8. Determine whether there are missing pulses. You can use an intuitive method: use a sharp knife to point a point on the workpiece blank, set the point as the work origin, raise the Z axis, and then set the Z axis coordinate to 0; repeatedly move the machine tool, such as empty tool running A typical machining program (preferably including three-axis linkage) can be paused or stopped during machining, and then returned to the workpiece origin, and the Z axis is slowly lowered to see if the tool tip matches the point on the blank. If there is deviation, please check the type of pulse signal received by the stepper driver, and check whether the indirect line between the terminal board and the driver is wrong. If you still feel stuck or lost steps, adjust the acceleration and other parameters according to steps 10, 11, and 12. ^[2]