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What Is an Actuator Stroke?

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  • Written By: Paul Scott
  • Edited By: E. E. Hubbard
  • Last Modified Date: 24 November 2016
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Actuator stroke is a quantitative term used to express the full length of working movement of which any actuator is capable. This operational variable is a critical consideration when choosing actuators or designing systems based on existing units. Actuators are either capable of fixed stroke values or may be adjusted to produce movement ranges suitable for the particular application. The stroke values of linear and rotary actuators are determined and expressed in different ways, with linear types generally being easier to measure. Some multi-turn rotary actuators don't have stroke values as such, but are rather defined by the number of full rotations that they produce.

The full extent of the working motion output of an actuator is known as its stroke. A thorough knowledge of the optimal, minimum, and maximum actuator stroke values for any application is critical for the safe, efficient operation of both the actuator and the mechanism to which it is connected. If an incorrectly-rated actuator is used, a loss of efficiency is generally the best case scenario. On the other end of the scale, destruction of the actuator, the actuated mechanism, or serious operator injuries are a distinct possibility if the actuator stroke is not suitable for the specific application.

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Fixed-stroke actuators produce a finite, pre-set range of motion. These devices are used where exact matches are possible between the actuator output and the actuation requirements of the secondary device. Other actuator types feature integral adjustment controls that allow the device's output to be set according to application requirements. In some cases, the actuator power supply may also be routed through travel limits that stop the actuator when it reaches the optimum stroke length.

Measuring an actuator's stroke can be tricky, particularly in the case of rotary devices. Linear fixed output actuators are the easiest examples to measure. To achieve this, the actuator is disconnected from the secondary device and its mechanism placed in the neutral or null position. The entire length of the actuator is then measured from its rear surface to the center of the actuator arm link pin. The device is then actuated to produce its full motion and re-measured, the difference between the two measurements being the actuator stroke value.

The actuator stroke of a rotary actuator is a little harder to establish. Those devices that develop less than a full turn of output motion feature stroke values expressed in degrees. There are several ways of establishing this value if it is unknown, one of which being the use of a specially-designed protractor template. For obvious reasons, multi-turn rotary actuators are not rated according to stroke length. Their output is expressed according to the number of complete revolutions that they produce.

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