Lead-Screw Linear Motor
An actuator type that converts the motion of a rotating electric motor into linear push/pull movement through a threaded shaft (lead screw). Because the screw thread is not back-drivable, it holds the load at the point where it stopped without consuming energy; it draws current only while moving. In the AXI ELF-812 kit, an actuator of this type drives the hydraulic control lever.
The motor shaft turns a trapezoidal or ball screw, and since the nut on the screw is prevented from rotating it slides back and forth. The travel per turn (pitch) is typically between 2–8 mm; as the pitch gets smaller the pushing force increases and the speed falls. Thanks to the high reduction ratio, a small DC motor produces enough force to move the lever.
- Self-locking behaviour: on a low-pitch screw it is not possible for the load to back-drive the shaft; the lever stays in the position you selected.
- Current profile: current flows only during movement, and the motor winding is not energised in standby. Since the manufacturer does not declare a current value for the ELF-812, we do not state an amp figure.
- Stroke limit: the range of movement is limited by the screw length, so during installation the lever's end points must be matched to the actuator's stroke limits.
This is the difference from the cable-pulling LFT20/LFT54 kits: there the motor pulls a cable 50–60 mm, whereas in the ELF-812 the linear actuator pushes the lever directly and holds its position. That makes it possible to keep a selected height repeatably in position mode.
Context in which this term is used: Converting a tractor hydraulic lever to electronic control