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The uc3717 chip from uNI_rRODE is designed for low-power bipolar stepper motor control, making it ideal for microcomputer interfacing. Its drive circuit is illustrated in Figure 1. The chip has several key pins: pin 1 (Bout) and pin 15 (Aout) are connected to the two ends of the motor’s phase winding. Pin 2 (T) is used for connecting the Rc timing component. Pins 3 and 14 (Vcc) provide power to the coil, ranging from 10 V to 45 V. Pins 4, 5, 12, and 13 (GND) are grounded. Pin 6 (Vcc) supplies power to the IC, while pins 7 and 9 (I0, I1) are logic inputs for setting the winding current. Pin 8 (Ph) controls the rotation direction, and pin 16 is connected to a current sampling resistor. The sampled signal is filtered through an RC low-pass filter and compared with an internal voltage reference on pin 10. Pin 11 (Vr) is an external reference voltage used for micro-step control. In full-step, half-step, and 1/4-step modes, Vr is typically set to +5 V.
The step size control of the uc3717 is achieved by selecting different combinations of I0 and I1, which determine the winding current. The truth table outlines how these settings affect the motor’s operation.
For position detection, an incremental photoelectric encoder is mounted at the end of the motor shaft. The position detection unit counts the pulses from the encoder, and the computer reads this data to calculate the actual movement distance. As shown in Figure 2, the encoder generates two pulse signals, A and B, which are out of phase by 90 degrees. These signals are used to determine the direction of rotation, with one pulse strobing the other to distinguish between forward and reverse movements. This process is handled by a pulse shaping and direction discrimination circuit, as illustrated in Figure 3.
In a three-axis positioning system, the computer sends position information through its I/O port to the control circuit, which drives the motors via couplings and ball screws to move the platform in X, Y, and Z directions. The laser head is controlled by the computer, allowing precise engraving on the workpiece. As shown in Figure 4, the system uses mechanical switches to detect the positioning limits on each axis. These switches are processed into logic levels by a gate circuit on the interface board, enabling the CPU to determine the reference point for the coordinate system.
The accuracy of the three-dimensional positioning depends heavily on the precision of the detection devices. To enhance performance, error models are developed based on the relationship between the device’s errors and system states. During operation, the CNC system calculates real-time compensation values using these models, adjusting the measured data to ensure high positioning accuracy for all axes.
In conclusion, the laser engraving machine relies on fast and accurate positioning for its operation. The use of high-resolution hybrid stepping motors, combined with micro-step control and photoelectric encoder technology, ensures stable and precise motion. The system is efficient, easy to maintain, and well-suited for industrial applications.
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