Leadshine’s CS-D series product is means Closed Loop Stepper Drive, offers an alternative for applications requiring higher performance and higher reliability than open loop stepper system, and it remains cost-effective. The matched stepper motors are NEMA17,23 and 24 combined with an internal encoder which is used to close the position, velocity and current loops in real time.
Traditional stepper systems operate in open loop condition provide position control without feedback from stepper motors to the controlling stepper drives. In a stepper system, the stepper drive keeps outputting preset current into the controlled stepper motor to move the attached load to the target positions. It does not know the current motor movement position, even when loss of movement synchronization (difference between desired move distance and actual moved distance) has happened and caused "Loss of Steps". Therefore, engineers have to make huge torque reservation (30-50%) to ensure "NO" loss of steps would happen. But because of the "open loop" feature of stepper systems, it is still commonly seen that loss of steps happens, especially in quick acceleration or quick torque require changes. That could result in wasting processed materials, crushing control systems, or even damaging machines. That's one of the main reasons limiting the adoption of stepper technology in many motion control applications.
In the past, when an application requires real-time closed loop "servo" operation, engineers are forced to choose servo systems at much higher costs and with more complexity. But in many applications, because traditional servo systems lack of high torque feature of stepper systems, high power servo motors have to be chosen, or expensive planetary gearboxes have to be added to achieve desired torque. In addition, hard to tune, hunting ("shaking when moving"), overshooting, and long settling time are also known problematic issues for many servo systems
With the implementation of high resolution encoders, Leadshine easy servo systems apply servo controls on stepper motors. In an easy servo system, the shaft position of the driven stepper motor is fed back to the controlling easy servo drive in real time (every 50 micro second for 1000 line encoders). The easy servo drive can then correct the position error, close the position loop between the drive & motor, and totally eliminate the possibility of loss of movement synchronization. Because Leadshine easy servo systems are actually hybrid of stepper and brushless servo systems, they inherit desired features available in both technologies. Leadshine easy servos are easy to implement (almost "plug and play"), low cost, high torque, high precision, no loss of steps, extra low motor heating, no hunting, no overshooting, almost zero settling time, broad application range. They have been successfully implemented in many industrial such as CNC machinery (CNC routers, plasma, laser engravers/cutters, grinding machines, milling machines, etc), semiconductor, medical, lab automation, packaging...
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In open-loop stepper systems, potential loss of motor movement synchronization limits their adoption for many applications. Engineers are forced to reserve 50% of available stepper motor torque to avoid possible loss of steps or stall. With the adoption of high resolution encoders to feedback real time motor shaft positions, Leadshine ES series easy servo drives close the position loops between servo drives and driven motors. That will keep motor movement synchronized all the time, and allow 100% of available torque.
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Due to closed loop control and adoption of advanced control algorithm, the ES series easy servo systems can always implement 100% torque of the motor, and do not need the huge 50% torque reservation in normal open-loop stepper systems. This feature significantly improves system high speed performance. While open-loop stepper systems are typically adopted in applications under 1,000 rpm, the ES series easy servo systems are ideal for many applications up to 2,000 RPM, sometimes even for 3,000 RPM!
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Also due to closed loop control and adoption of advanced control algorithm, the ES series easy servo systems can always implement 100% torque of the motor. This feature significantly improves system response or acceleration performance, usually up to 30% quicker or higher acceleration than a same size and holding torque conventional steppers.
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In open-loop stepper systems, output current to the stepper motor from the step driver is constant. No matter what load condition is and how much current is needed, the stepper drive will always output a constant current.
Since the ES easy servo runs in closed-loop, the ES drives only put as much current into the motor as required to drive the motor to the target. Motor heat is 20 to 40 oC lower compare to a conventional stepper drive which runs at full current most of the time. Less power consumption and longer motor lifetime can be achieved, reducing using and maintenance cost.
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