FAQs for linear actuators / linear drives

WHICH ACTUATOR MODEL SHOULD I CHOOSE?

Many factors play a role when choosing a linear actuator.

To summarize a few simple rules:

• For simpler applications, light to medium duty and lower cost, you should choose the LMR or ATL types. The LMR has integrated limit switches.
• For heavier loads with integrated limit switches, choose the CLA.
• For higher forces and medium loads, choose the ATL with ACME thread.
• For high duty cycles, select ball screw drives.
• For high speeds, select servo-driven actuators of type UBA or SA.
• For high dynamics with short or long strokes or as a replacement for pneumatic/hydraulic cylinders, choose SA servo-driven actuators.
• For very high forces and/or long strokes, select type ILA.
• For outdoor sun tracking, choose the TMA type.

WHICH MOTOR TYPE IS THE BEST?

Standard asynchronous motors with IEC frames are the most cost-effective and suitable for most applications. Three-phase motors are more economical and offer better performance than single-phase motors. DC drives are ideal when no mains supply is available. When power requirements increase, brake motors may be required, especially the UBA type, which is reversible. Finally, servomotors can be used for high dynamics and precision.

IS REVERSE TRAVEL POSSIBLE? ARE ACTUATORS SELF-LOCKING?

Actuators of the ATL type work with worm gears, and in this area it is notoriously difficult to be precise. In general, we define self-locking when an actuator does not move under a statically applied push or pull load. Dynamic self-locking is when an actuator remains stationary when the motor is switched off, even under the effect of a load.

To summarize, most ATL and CLA actuators are statically self-locking, but not necessarily dynamically self-locking, depending on the load. Most BSA drives are not self-locking and a brake motor may be required. All UBA and SA drives are not self-locking.

WHAT SPEED ACCURACY DO LINEAR ACTUATORS ACHIEVE?

This depends on the type of motor. DC motors vary their speed depending on the load. Depending on the model, the speed can decrease by 20-40% compared to the rated speed when the load is increased. Diagrams are available. AC asynchronous motors have only a small speed variation with changes in load. Usually 2-3 %. Servomotors can maintain speed very accurately depending on the control system.

DOES THE STROKE OF LINEAR ACTUATORS NEED TO BE LIMITED?

Yes - these industrial actuators are not designed to be driven to their internal limits, which can cause damage.

The use of limit switches that switch off the motor is recommended. There are several alternatives:

• Installation of limit switches in an external mechanism.
• Small drives of type LMR and CLA have integrated limit switches.
• Fit magnetic limit switches to the linear actuator. These fit around the outer tube and detect the position via a magnet that moves with the push rod. They are easy to adjust.
• Use an external limit switch built into the actuator. This is a standard option for ATL actuators.
• For larger actuators, inductive proximity switches can be used. These can be more economical for large actuators, but are not adjustable.

For high speed actuators, the position of the limit switch may be exceeded, so position feedback via an encoder should be considered.

If there is a likelihood of external loads blocking the drive in the middle of the stroke, the use of a safety clutch should be considered.

WHAT OPTIONS ARE THERE FOR THE END FIXING?

A hardened steel rod end or a hollow threaded end are the most economical solutions. Optional rear brackets are available for a pivoting connection. Care should be taken to ensure that the end fixings do not twist the actuator during the stroke.

Alternative fixings at the front end, such as ball joints and flanges, are available if they can support the connection to the machine.