Stepper motors control speed, position, and direction by receiving pulsed currents. The number of pulses determines the stepper motor's position, the pulse rate determines its speed, and the pulse direction determines its rotation. Currently, most stepper motors are controlled by a PLC sending pulses to a driver, which then drives the motor. While pulse-based control has been around for decades, it's no longer sufficient for demanding applications, necessitating bus-based control.
For applications requiring numerous motors, such as medical devices with twenty to thirty axes, pulse-type control is problematic. Firstly, it's difficult to control; a single PLC can only control six or seven axes at most, and multiple motors necessitate multiple host computers, requiring significant space. Most medical devices are compact and lightweight. Secondly, the wiring for pulse-type systems is complex, leading to signal interference and equipment instability. A bus-type system, however, requires only two signal lines and a power line to connect all motors in series, simplifying design and installation while eliminating the signal interference issues associated with extensive wiring.
Some machines have their own built-in computer host. If a pulse type is used, the computer host cannot be used effectively, and a host computer or motion control card is needed to control the stepper motor drive system. However, a bus type can be directly controlled through the computer host, which has the professional performance of the motion control card method, and also has a significant advantage in cost and space compared to the other two methods.
Some products require torque mode during operation. For example, some screw fastening machines use torque mode. Pulse type cannot control the motor current to adjust the torque, while bus type can.
Compared to pulse-type control, bus-based control is not only much smaller in size, but also much simpler to program than PLC ladder logic. Furthermore, it allows for real-time feedback of motor current, voltage, temperature, and stall conditions; real-time changes in current and microstepping; and simple control features such as S-curve acceleration/deceleration, analog signals, synchronization commands, and offline control. In summary, bus-based control offers many new functionalities with no significant disadvantages compared to pulse-type control, making it the future direction and trend for stepper motor motion control.
