Engineering Notes by Oriental Motor

Improving Stop Accuracy for Start/Stop Conveyors (VIDEO)

[fa icon="calendar"] May 7, 2019 1:32:29 PM / by Johann Tang

Johann Tang

Are you using motors for a start/stop conveyor or similar application?  While AC motors are a common choice for conveyors, there is a unique speed control motor solution available that could improve stop accuracy as well as reduce footprint and cost of machine designs.

CHALLENGE
Improve stop accuracy

First, let's understand the main challenge of a start/stop conveyor, which is maintaining a good, repetitive stop accuracy.  In this application example, we use a material handling conveyor that moves when there is no load detected by the sensor, and stops when there's a load detected.  This type of conveyor is frequently integrated with a robotic arm for a pass/reject quality control process, or a pick and place process.

Application Example: Start/Stop Conveyor with Sensor Control

  • Conveyor moves when there is no load detected by the sensor.
  • Conveyor stops when load is detected by the sensor.

A motor with inconsistent stop accuracy or excessive overrun could cause the robotic arm to pick up the wrong product.  With AC motors, a difference in inertial load can also change its overrun characteristics, which requires physically moving the sensor location to adjust for position accuracy.

CVK-SC sensor stop conveyor

CVK-SC timing chart for decel, stop

Stepper motors aren't usually considered for speed control, but its high responsiveness can improve stop accuracy for low speed or frequent start/stop applications.  Unlike AC motors, the difference in inertial load will not change the stopping characteristics. 

Here we compare the overrun characteristics of AC motors vs stepper motors.

CVK-SC overrun, stop accuracy table

SOLUTION
Use a stepper motor with a simplified speed control driver

Oriental Motor's CVK-SC Series uniquely combines a high torque 5-phase PKP stepper motor with a simplified version of the compact CVD bipolar microstepping driver that operates easily like other speed controllers.  The CVD speed control driver does not require an external pulse generator.  Instead, 2 stored speed settings (0.02~600 RPM) and acceleration/deceleration rate (0~3 seconds) can be set with rotary and dip switches.  The stepper motor offers better response and stopping accuracy than AC or brushless motors and provides holding torque while the driver's Smooth Drive function ensures low vibration performance.  Due to the efficient design of the driver, the CVK-SC Series can run continuous duty cycles without overheating (at full current setting in most cases). 

In summary, the high torque density of stepper motors and the compact, standalone design of a speed control type driver can help reduce footprint and simplify designs for low speed applications.  Please consult with our Tech Support Engineers to see if it's the right solution for you.  

Notable Features:

  • No pulse generator needed
  • Continous duty is possible
  • +/-0.8% speed accuracy
  • Low vibration
  • High stop position repeatability
  • Holding torque
CVK-SC Series stepper motor and driver

CVK-SC Series Speed Control Stepper Motors

Watch how easy it is to operate a CVK-SC Series motor and driver!

04_CVK SC_US_0420

Among many improvements in design, the minimized air gap, optimized stator/rotor ratio, and high density winding of the stepper motor increases torque while the driver's Smooth Drive and improved current control features minimize vibration and increase accuracy.  Furthermore, the efficient design of the dedicated drivers allow continuous duty operation without the need for heat sinks.

Learn more about the design of these high torque stepper motors or drivers.

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Topics: Conveyor, AC Motors, Stepper Motors, Stepper Motor Drivers, Speed Control, VIDEOS

Johann Tang

Written by Johann Tang

Johann Tang is a Product Specialist at Oriental Motor USA Corp. with over 15 years of knowledge and experience supporting applications of various types of electric motors, gearheads, actuators, drivers, and controllers.