Why do we combine a servo motor with a gearbox

Tuesday - 06/03/2018 21:16
Do you know why we still use today gearboxes while servo motors becoming stronger and more advanced? The gearboxes of Dolin are used in many cases in combination with a servo motor, for example because they have low backlash and are able to deal with high torque.
Gear Redcer Motor
Gear Redcer Motor
But still we did not give an answer to the previous question: why! In this article we discuss the operation of a servo drive and translate this through to the gearboxes.
 
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What is a servo-drive?
 
The prefix servo comes from the Latin servus which means slave or servant. Technically translated tis means to follow or execute a command. A servo motor follows the (complex) task given to him.
 
For industrial applications, servo motors are used where a drive-system has to be accurate or highly dynamic. The feedback to the motor is done through a resolver (analogue sensor of rotation) or encoder (digital sensor of rotation). A servo motor is controlled by a servo amplifier, possibly with a shaft controller.
 
The rotation frequency of the actuator is given back by the resolver or encoder. This is capable in addition to the rotational speed, also to determine the position of the rotor and the direction of rotation.
 
Small Gear motor Horizontal Type Ac Gear Motor
 
The servo amplifier compares the set rotational frequency with the measured rotational frequency. Now the servo amplifier can drive the actuator to the desired values.
 
Difference between a stepper motor and servo motor

There is a misunderstanding that a stepper motor is a kind of servo motor. This is not true; a stepper motor does not give any feedback ! Feedback is typical for servo motors, exactly what “servus” stands for.
The various servo motors

There are roughly two types of servomotors (actuators), operating on direct current (DC servo motor) or alternating current (AC Servo Motor). The table below is showing the main features:
Motor Advantages Disadvantages
 
DC Servomotor for very large capacities Uses brushes
  Precursor of servo technology DC Power supply
    Expensive motors
    Maintenance sensitive
 
AC Servomotor Low inertia Not worth mentioning
  High speed possible  
  Fast torque  
  High termal load  
  Compact housing  
  Low maintenance

Interesting, AC Servo Motors have no significant disadvantages more! So, why would you use a gearbox? This has the following reasons:

    If you want a very low speed, possibly in combination with a higher torque.

    If you need high torque. (Actuators with high torque are available, but they are exponentially more expensive compared to the smaller servomotors)

    Inertia matching, in order to prevent that the load determines the behaviour of the motor.

    In order to absorb the high radial or axial forces of the application.

    If you want to go “around the corner” otherwise the servomotor sticks out the application. Gearboxes are available in right-angled versions.


Why a gearbox is essential when using a servomotor

Almost every robot as we know it is equipped with servo technology, which enables them to move faster, more accurately and without interruption. Gearboxes are needed to translate the high speed of the motor in a controlled movement of the arm, for example to pick a product.

Without a gearbox, the mass and velocity of this arm will demand the behaviour of motor and it will literally overshoot the target.

What are the criteria using a gearbox for a servomotor?

    Low backlash during the life time!

    It makes no sense to build a high-precision motor with a high backlash gearbox. The play is indicated in arcminutes, where one arc minute is 1/60th of a degree. One arcminute is approximately 25 mm deviation at a radius of 100 meters!

    High repeatability accuracy.
    Better end product
    Low inertia!

    The motors are able to regulate very dynamic. This is extinguished if he has trouble getting the gearbox speed changed. An oil tanker has a high inertia and is difficult to change direction, a Jet-ski has a low mass inertia and is suitable for fast movements.

    High efficiency!

    Servo Technology is not cheap. With a high efficiency gearbox, the motor, cables and amplifier remain relatively small which means the amount of investment remains interesting.

    High torques!

    Servo motors are relatively strong and this torque is multiplied by the ratio of the gear. Therefore, the gearbox is able to handle high torque. Taking account of the radial load.

    Low noise!

    Often servo technology is used wherever people work, such as operators. A low noise level is very reassuring, or it is even a health and safety obligation.

    Suitable to withstand high torque emergency stops
    Low break-away torque
    Maintenance free throughout its lifetime
    Easy and flexible installation

A servo drive = A servo motor with a gearbox.

The gearboxes of Dolin meet all the above criteria and are thus fully suitable for use with a wide variety of servo motors. Our customers and partners already know that even more is possible. The market knows Dolin is running harder, which means we guarantee proper delivery, excellent service and high quality. Do ask yourself what gearbox you choose next time?

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