Micro linear actuators are designed to solve a specific engineering challenge: delivering precise linear motion inside a footprint too small for conventional devices. But when an actuator encounters an unexpected obstruction, an external hard stop, or a mechanism jam, the electrical energy feeding the motor has to go somewhere.
On a larger scale, engineers use mechanical safety clutches or thermal cutouts to absorb jams. In micro-scale motion, that approach fails. Mechanical clutches are impractical to add to a sub-50g unit. Thermal cutouts are equally ineffective: in micro actuators, especially ones with high gear ratios, the device itself would more likely fail mechanically before the motor windings generate enough heat to trip a switch.
Protecting a micro actuator requires moving overload protection out of the internal gearbox and onto the system boundary through smart electrical controls and mechanical design.
The Fallacy of the Actuator as a Fuse
It would be a mistake to assume a micro actuator will simply stall safely if it hits a hard stop. While it may stall, the mechanical force generated at the gear train during a sudden stop, particularly on high gear ratio models, can exceed the yield strength of miniature gears.
Using the actuator shaft as the mechanical backstop for a mechanism forces tiny gear teeth to absorb full motor torque plus the kinetic energy of the moving assembly. Protection must intervene before that mechanical stress reaches the internal gears.
Smart Electrical Limits: Stall Detection and Inrush Headroom
The cleanest way to prevent mechanical overload is at the drive level. Because DC motor current scales with mechanical load, monitoring current or position progress allows a controller to cut power the moment a jam occurs.
However, setting an electrical cutoff requires accounting for inrush current - the brief spike in power when a motor first starts up to overcome static inertia. If a system trips instantly on any current spike, the actuator would likely not function at all.
Boundary Limits: End-of-Stroke vs. Mid-Stroke Jams
Actuators with built-in limit switches (-S series) automatically cut power when the drive nut reaches the factory ends of its stroke. If the required stroke is below the full stroke of the device, external limit switches can be used to set custom end of stroke points. However, limit switches only work when they are triggered; they cannot detect an obstacle or obstruction mid-stroke.
If an actuator is driven into a hard stop midway through the stroke, the actuator will continue driving until it stalls. As mentioned previously, this can result in damage to your actuator, especially if repeated.
Mechanical Compliance: Inline Spring Tips
Electrical shutoffs and limit switches prevent sustained stalls, but they require milliseconds to react. To cushion sudden rigid impacts during that brief window, mechanical compliance can be built into the load point.
An inline spring tip places a calibrated compression spring between the actuator shaft and the load. When the actuator drives into a hard stop, the spring compresses, absorbing the initial shock and converting a sudden force spike into predictable mechanical deflection. This buys time, giving the control board enough stroke margin to register the stall or trip a limit switch without smashing the gears.
Frequently Asked Questions
What happens if a micro linear actuator stalls under load?
When a micro linear actuator stalls, current spikes to its maximum draw. If allowed to persist, this high current generates heat in the motor windings and places severe mechanical stress on the miniature gear train, which can strip gear teeth or burn out the motor over time.
Why shouldn't I use a mechanical safety clutch on a micro actuator?
Mechanical safety clutches add significant weight, physical size, and wearing parts. On a micro actuator weighing as little as 28g to 56g, adding a mechanical safety clutch destroys the compact footprint and weight advantage that justified selecting a micro actuator in the first place.
How does the LAC board detect an actuator stall?
The LAC board uses closed-loop position feedback from -P or -I series actuators. Rather than relying solely on current spikes, the board tracks actual motion. If the board commands movement but position feedback fails to advance within a calibrated time frame, it identifies a stall and cuts motor power.
Do internal limit switches protect against mid-stroke jams?
No. Internal limit switches on -S series actuators only cut power when the drive nut reaches the physical ends of the actuator stroke. If an obstruction occurs mid-stroke or against an external hard stop, an internal limit switch will not trigger.
How is an external limit switch kit used?
An External Limit Switch Kit allows you to mount physical switches anywhere along a mechanism's movement path or on external hard stops. Wiring these switches directly to the actuator power line cuts motor current instantly when a specific mechanical boundary is reached, regardless of where the actuator nut is along its internal stroke.
Can you offer spring tips for Actuonix actuators?
We do offer custom product development and have made spring tips for our clients. Reach out to our sales department to talk more about the process and requirements.
Need Assistance With Your Project?
If you need help choosing the best actuator for your application, reach out to our sales department. They’ll be happy to assist you in selecting the best linear motion solution for your application.
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