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  MEZ Servo System - Closed Loop Stepper          
  • By adopting high resolution encoders, MotionKing MEZ (MotionKing Easy) servo products apply servo controls on high torque stepper motors. Those products combine advantages of brushless servo systems and conventional stepper systems. MotionKing easy servo products are featured with closed position loops, high starting & low speed torque, no torque reservation, high stiffness at standstill, extra low heating, smooth motor movement, no hunting, no overshoot, zero settling time, and no tuning for most applications. You can click above tabs to read details about what are MEZ servo, and their advantages over stepper systems & servo systems. MotionKing's MEZ servo products are available in MEZ servo drives and MEZ servo motors.
  • 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, MotionKing MEZ servo systems apply servo controls on stepper motors. In an MEZ servo system, the shaft position of the driven stepper motor is feedback to the controlling MEZ servo drive in real time (every 50 micro second for 1000 line encoders). The MEZ 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 MotionKing MEZ servo systems are actually hybrid of stepper and brushless servo systems, they inherit desired features available in both technologies. MotionKing MEZ 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...
  • 1. Closed-loop, eliminates loss of synchronization
    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, MotionKing MEZ series 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.
    2. No torque resovation for broader operating range
    Due to closed loop control and adoption of advanced control algorithm, the MEZ series 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 MEZ series servo systems are ideal for many applications up to 2,000 RPM, sometimes even for 3,000 RPM!
    3. Quicker Response, Higher Acceleration
    Also due to closed loop control and adoption of advanced control algorithm, the MEZ series 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.
    4. Extra low motor heating
    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 MEZ servo runs in closed-loop, the MEZ 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.
  • 1. Quick response, no hunting
    For the case of conventional servo motor systems, there is a considerable delay between the commanding input signals and the resultant motion because of the constant monitor of the current position, necessitating a waiting time until it settles, called settle time. Since the MEZ servo is a stepper motor based system, it operates in synchronism with command pulses and has no hunting problem. When it stops, its position is completely stable and does not fluctuate. It is a great feature of the MEZ when rapid motions with a short distance are required and it is ideal for applications such as bonding and vision systems in which hunting would be a problem.
    2. High torque at starting and low speed, high inertial loads
    Since the MEZ servo system is a stepper motor based system, so it has the advantages of high stiffness at standstill, high torque at starting and low speed, eliminating gear box. The MEZ adopts sophisticated control algorithms to take advantage of high-torque capability, providing direct-drive of high inertia loads such as flywheels and belt drives. These load inertials may be as large as 100 times the motor inertia while still providing smooth positioning control. Conventional servo systems typically cannot exceed a 10:1 inertial mismatch.
    3. Plug and play, no tuning for most of applications
    Unlike a servo system which usually needs the engineer to spend a long time to learn how to use tuning tools and tune the gains for a satisfying performance, the MEZ series servo is ready for operation within a very short period of time. Set the microstep resolution and operating current, then the system is ready and offers high performance approaching to a fine tuned servo. Save time and save cost.
(Stepper Motors with Encoders)

MotionKing offers MEZ servo motors (stepper motors with an encoders) from NEMA 17 to 43 with torque of 0.5 to 20 Nm (70 - 2,832 oz-in). Those easy servo motors are integrated with 1,000-line encoders. They are made of high quality materials and can move in high precision with smoothness and quiteness. When driven by MotionKing's MEZ servo drives, position cloops are fully closed.

(Closed Loop Stepper Drives)
MotionKing offers MEZ servo drives (closed loop stepper drives) providing servo controls on stepper motors. Those easy servo drives combine features of both traditional stepper and brushless servo drives and are featured with no loss of movement synchronization, load based output current, extra low motor heating & noise, no overshooting, no hunting, zero settling time, etc. They are available in DC input or 110/120 or 220/230 AC.


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