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An actuator arm is the part of any actuator that physically transfers the actuator's action to the mechanism that it is designed to operate. In some cases, the actuator arm may be part of the actuator's internal mechanism, or a separate linkage or series of linkages. Depending on the range of actuation movement, the arm will attach to the actuated part with either a fixed or an articulated joint. Actuator arms may be a few inches to several feet long depending on the specific application. Although unrelated, the term may also be used to describe the pickup arms on a computer hard drive reader mechanism.
Actuators are used in industrial, manufacturing, and domestic applications to remotely control a wide variety of machine functions. They may feature electric motors, hydraulic or pneumatic pressure, and electromagnetic force as driving mechanisms, and may range in size from tiny examples which fit in the palm of the hand to huge industrial examples several feet in length. Some actuators provide simple straight-line movement, while others have rotary or sophisticated, variable outputs. All, however, share one common design feature in the linkages or actuator arm mechanisms used to transfer the actuator energy to the device being operated.
Most actuator types consist of a driven internal mechanism that produces the motion used as an actuation force. These mechanisms are usually enclosed in a sealed casing that will mount separately from the device that it is to actuate. To transfer the actuator's internal movement to the secondary device, an actuator arm is used. This part of the actuator serves as a physical link between the two and may be an extended part of the internal mechanism or a series of individual linkages.
The method used to join the actuator arm to the secondary device also depends on the design specifics of the system. If the full range of motion involved is in a straight line, a fixed joint may be used. Where the actuated mechanism moves through an arc or rotary outputs are involved, the joint may be of a ball-and-socket or yoke-and-pin type, allowing for articulated motion. In most cases, systems are designed to keep actuator arms as short as is possible. In some cases, though, this is not possible and very long actuator arms have to be used. Where these long arms are used, they will often pass through guides or bearings that support them and maintain their rigidity during actuation.
Another use of the actuator arm term is the description of computer disc reader extensions. They are used to hold the reader pickups and span the storage disc. These arms are usually set up in stacked groups and are made from thin, flexible metal.