Linear actuators with absolute encoders

An open-loop stepper actuator knows where it is only by counting the steps it was told to take. Add an absolute encoder and the axis knows its position the instant power comes on, verifies every move, and never needs a homing cycle. Here is what that buys, what it costs, and which LYNX actuators ship with it.

Open loop, incremental, absolute

Open-loop stepper. Position is inferred from commanded steps; a stall, a bump, or a power cycle loses it, so every start begins with a homing move to a limit switch. Fine for many lab and light-duty axes. Incremental encoder. Counts pulses from a known reference; detects a stall or missed step in real time, but still needs a home after power-up because the count starts at zero. Absolute encoder. Reads a unique position code on every revolution (multi-turn versions across the whole travel), so the controller knows the carriage position at power-up with no homing, no limit-switch search, and no risk of starting a move from the wrong place.

What it changes in practice

Homing time disappears. A 1,275 mm axis homing at 100 mm/s spends up to 13 s finding its switch — on every start, after every e-stop. With an absolute encoder the first move is a real move. Collisions become detectable. The controller compares commanded and actual position every cycle; a stall from a jammed gripper stops the axis instead of silently losing steps and crashing on the next move. Recovery after a fault is safe. After an e-stop in the middle of a deck, the axis knows exactly where it stopped and can retract rather than re-home through the labware. For multi-axis gantries over a loaded deck, that last point is usually the reason to specify it.

Stepper with encoder, or servo?

A servo is closed-loop by definition — its encoder is how it works — and the BLC-TC controllers run servo axes at 48 V with continuous torque nearly flat to 2,500 mm/s. A stepper with an absolute encoder keeps the stepper's price and holding torque and adds position verification and homing-free start-up without the servo's tuning. The engine sizes both from the same spec and shows the delta: on an SBAC45 270 mm it is $200 per axis. If the application needs the speed or the torque-at-speed, choose servo; if it needs the position certainty on a stepper budget, choose the encoder stepper.

Specifying it in the engine

Say "absolute encoder" or "no homing" when you describe the task, or pick an SBAC part by name. The engine selects the encoder variant where one exists, applies the $120-per-axis upgrade where it does not, chooses a controller that reads the feedback, and prices the system. The Engineering Assumptions panel records the choice so the quote and the BOM agree.