What are the key points of servo motor selection? Introduction to the steps of servo motor selection

During the operation of the robot, the servo motor is used to drive the robot to achieve multi-degree-of-freedom movement. If the robot's movement speed and accuracy are required to be high, the servo motor's response speed and control accuracy must be high enough. Therefore, when choosing a servo motor, you must consider the problem carefully.

What are the key points for selecting servo motors?

Some systems such as conveyors and lifting devices require the servo motor to stop as quickly as possible. However, the servo motor has no regenerative braking and cannot decelerate the motor in the event of a fault, emergency stop, or power failure. At the same time, the mechanical inertia of the system is large, so the dynamic brake should be selected based on the weight of the load, the working speed of the motor, etc.

Some systems need to maintain the static position of the mechanical device, which requires the motor to provide a large output torque and a long stop time. If the servo self-locking function is used, it will often cause the motor to overheat or the amplifier to overload. In this case, a motor with electromagnetic brake should be selected.

Some servo drives have built-in regenerative braking units, but when regenerative braking is frequent, it may cause the DC bus voltage to be too high, and a regenerative braking resistor must be added. Whether a regenerative braking resistor needs to be added and how large it should be can be determined by referring to the instructions for use of the corresponding sample.

If a servo motor with an electromagnetic brake is selected, the motor's moment of inertia will increase and should be taken into account when calculating the torque.

Industrial robots are used very frequently and often work 24 hours a day, so the quality requirements for robot parts are very high. The servo motor is the core device of the industrial robot, so the selection of servo motor becomes particularly important. In order to choose high-quality servo motors, you can also choose from multiple indicators such as price, weight, and volume.

Introduction to the steps of servo motor selection

According to the operating conditions, select the appropriate load inertia calculation formula to calculate the load inertia of the mechanism.

Select the appropriate servo motor specifications based on the load inertia and servo motor inertia.

Combine the preliminarily selected servo motor inertia and load inertia to calculate the acceleration torque and deceleration torque.

Clarify the motion conditions required for the load mechanism, i.e. the speed of acceleration/deceleration, movement speed, weight of the mechanism, movement mode of the mechanism, etc.

The load torque is calculated based on the load weight, configuration, friction coefficient, and operating efficiency.

The maximum output torque of the initially selected servo motor must be greater than the acceleration torque + load torque; if it does not meet the conditions, other models must be selected for calculation and verification until they meet the requirements.

The continuous instantaneous torque is calculated based on the load torque, acceleration torque, deceleration torque and holding torque.

The rated torque of the initially selected servo motor must be greater than the continuous instantaneous torque. If it does not meet the conditions, other models must be selected for calculation and verification until they meet the requirements.

Complete the selection.

Stepper motors generally do not have overload capacity. AC servo motors have strong overload capacity. Take Panasonic AC servo system as an example, it has speed overload and torque overload capacity. Its maximum torque is three times the rated torque, which can be used to overcome the inertia moment of the inertial load at the moment of startup. Because stepper motors do not have this overload capacity, in order to overcome this inertia moment, it is often necessary to select a motor with a larger torque when selecting a stepper motor. However, the machine does not need such a large torque during normal operation, which results in a torque waste phenomenon.

1

Q; Causes of servo motor overload alarm

The drive transmission resistance is too large, check the transmission system.

2

Q: Is servo motor overload necessarily related to current?

As a torque output element, the overload of the motor must be that the shaft torque of the mechanical part is large and exceeds the value allowed by the motor, which has nothing to do with the current. However, the phenomenon is characterized by an increase in current, or equal to or exceeding the rated current. Usually, when the motor is configured and designed, the selected electric torque is 10~15% greater than the shaft torque of the machine. Therefore, when the motor operating current reaches or slightly exceeds 85% of the rated current, it can basically be considered that the full load of the machine has been reached. When it exceeds 90%, it can be considered as a mechanical (equipment) overload.

3

Q; Problems that may occur when the servo motor is overloaded

If the protection does not work, the motor does not rotate, the motor temperature rises, and after reaching a certain temperature, it remains in this state.

4

Q: What is the reason why the servo motor loses control and stops working?

The motor does not move. Check whether the servo amplifier alarms. If so, find a solution based on the error code. It may be an overload alarm. Try increasing the rigidity parameter.

5

Q: The servo motor has not started yet, but it is generating too much heat in the static state, causing a servo overload alarm. What is going on?

The servo motor started to receive the operation command and started to run, but the motor failed to run normally. Therefore, the electrical energy flowing to the motor was converted into heat energy and released, causing the motor to overheat.

This is divided into the following situations:

First, after the operation command is given, the following possibilities may occur: the parameter setting is inappropriate; the wiring is incorrect; the servo motor has low power and cannot pull the load;

Second, no operation command was given. At this time, the power was only turned on, and no operation command was given. However, due to wiring errors or electromagnetic interference, the servo system was disturbed and lost control.