The Usual Suspects in Electric Actuator Failure

From manufacturing machinery and agricultural equipment to electric cars and robots, the electric actuator drives the modern world – literally and figuratively. This reliance is not likely to change any time soon. It means that a deeper understanding of the workings of electric actuators will become increasingly necessary.

In developing this deeper understanding, learning about the common problems of electric actuators is crucial. For those with stakes in industrial ventures, in particular, knowing why an electric actuator is not functioning at peak condition will help reduce downtime and improve overall productivity.

This article will discuss the most common issues that may affect an electric actuator’s performance.

Electric Actuator Parts

A good first step in understanding what is wrong with a malfunctioning electric actuator is learning about its parts, especially those that usually exhibit problems.

There are two main categories for the basic parts of electric actuators: the electric system, which includes the drive and the motor, and the mechanical system, which includes the couplings and the actuator.

Motor

The motor driving an electric actuator creates the rotary motion through the rotation of the spindle or the rotor. The motor, through the driveshaft, is connected to a helical screw that subsequently rotates in a ball screw nut. The ball screw nut is driven forward or backward as the spindle rotates. The linear actuator moves following a hollow piston attached to the ball screw nut.

The power of the motor and the torque it generates dictate the force of motion. More powerful motors usually have different applications than those that create less torque.

Drive

The electric drive controls the motor. It creates variations in rotational speed and torque which, in turn changes the speed and force generated by the linear actuator. These variations are essential to adapting the actuator to different applications.

A feedback mechanism, usually in the form of an encoder or resolver, provides positional information to the drive to manipulate the actuator into a commanded position.  The drive can then be programmed to move, stop, or return to its resting or home position.

Couplings

Couplings are used connect the rotary motor to the ball screw of the electric actuator.

They are made from various materials, such as aluminum, stainless steel, and other metals. Suitable couplings are necessary for precision operations. They can affect the smoothness of acceleration, speed control and variation, the limit of the load, and shock and vibration isolation. They are also needed to synchronize actuators better.

Actuator

The actuator, often referred to as a linear actuator, converts rotary motion from the motor into linear motion for different applications, depending on the force, speed, load capacity, friction resistance, and other factors. 

Actuators transmit the speed and torque provided by the motor to a variety of drive mechanisms including screw, belt and rack and pinion power transmission systems. The base components of a linear actuator consist of the actuator body, a method of power transmission (screw, belt or rack & pinion), bearings to support the screw, a bearing system to support the load and a carriage to which related components can be mounted.  Manufacturers are generally able to vary method of power transmission as well as the bearing structure to provide different speed and load carrying characteristics based on the application requirements.

Common Issues with Electric Actuators

Issue: Cantilevered load

Common cause: The actuator is undersized for the load.

An undersized actuator most likely causes a cantilevered load issue. Sizing actuators correctly for the application is a crucial factor often neglected in favor of cost-efficiency. However, an undersized actuator will not be able to operate.  Most actuator manufacturers provide the user with software based sizing tools to help select the proper actuator to meet the criteria of the application.

To find the correct actuator size, it must be able to do the following:

  • Consistently support the dynamic and static loads being applied to it
  • Develop sufficient speed and torque throughout the range motion to support the application
  • Meet service and safety factors that can either be established by the manufacturer or the end-user

Issue: No belt movement

Common cause: Too much applied motor torque has stripped the belt or the belt is improperly tensioned

If the belt is not moving, the most common cause is that the motor is producing too much torque, which strips the belt of its teeth. It can be addressed by confirming the torque specifications of the motor do not exceed the maximum torque input specifications of the actuator and adjusting as necessary.

The issue can also point to the belt not having the correct belt size or proper belt tension. Belts have working and tensile strength ratings that need to be considered when employed in industrial applications.  In rodless actuators, bad manufacturing may cause a lack of belt movement.

Issue: Particulates present in the actuator

Common causes: The belt is exposed, or there is no positive air pressure to remove the particulates.

When particulates are getting into the actuator system, the cause is most likely the exposed belt. Exposed belts attract particulates from the environment. Once these particulates get inside the actuator, operations may be compromised.

Another common cause is that there is insufficient or no positive air pressure in the system necessary to remove the particulates.

Issue: Burned out motor

Common causes: Motor has an improper duty cycle or has the wrong voltage. There may also be contamination in the system.

Burnouts can be caused by motors with improper duty cycles, or the percentage that represents how much time the motor can operate compared to how much time it needs to rest. The manufacturer provides duty cycle limitations. They should be taken into consideration when choosing motors for different applications.

The wrong voltage can also cause motor burnouts. Burnouts may occur when a motor receives voltages higher than the recommended amount.

Contamination of particulates can cause more resistance and demand more torque from the motor. It can ultimately cause burnout if enough particulates enter the system.

Issue: Components fail

Common causes: Old age, incorrect sizing, and sustained heavy use of components

When electric actuator components fail, there can be different causes. The first one is the age of the component. Over time, components wear out and will need replacement. The second cause is sustained heavy use. When components are used past their recommended ratings, they are prone to failure.

Incorrect sizing is also a common cause of component failure. Actuators operate on precise measurements. Even minute disparities can eventually cause component failures.

Conclusion

Electric actuators have a lot of uses across different industries. It is important to be familiar with their everyday problems to keep downtime at a minimum. Understanding the basic parts and how they can fail is one of the most essential steps in preventing issues. An electric actuator can encounter issues with sizing, wear and tear, contamination, incompatibility, and more.

That said, while it is good to develop an understanding of the electric actuator, it’s best to leave the diagnosis, repair, or replacement to professionals like JHFoster. We have been equipping businesses since 1938. We are experts in industrial automation and compressed air systems.

For questions about electric actuator issues and other problems, reach out to our team.