How a PCB works in an industrial electric actuator

Controlling an actuator is based on an integrated controller or H-bridge, that changes the polarity of the voltage to the DC motor. Here you can benefit from low-current switching, since a high digital signal of only a few mA will cause the actuator to run.

The integrated H-bridge opens a variety of control options from the PCB such as speed and ramping.

This is the H-bridge, and in the middle is the power connection to the motor's positive and negative terminals. Four switches, in this case transistors, are connected to the power supply at the top and in the bottom of the H-bridge. These transistors replace the functionality of mechanical relays. The H-bridge controls the in and out movements of an actuator in a fairly simple way. When power is on two of the transistors must be activated to make the current flow diagonally – past the motor connection – making the motor run in one direction. To change directions, the current flow must be changed by deactivating the previously activated two transistors and activating the other two.

One of the most important things to know about an actuator is its position. The physical position of a PCB controlled linear actuator is based on Hall effect sensors, counting the number of pulses per spindle revolution.

Traditionally, electrical switches were mounted at each end of the spindle which calibrated the positioning system every time a physical end stop was reached. To ensure reliable position feedback from the actuator, it was required to have at least one of these end-stop switches activated on a regular basis. If not, the position feedback could drift over time due to Hall pulses on the encoder being missed, predominantly while powered down.

Because of this limitation, an application where the actuator did not make use of the full stroke could result in inaccurate position feedback over time.

A new initialisation principle, developed by LINAK^®, has changed the way linear motion can be initialised. It takes advantage of a small magnet mounted in the spindle nut, which moves past two Hall sensors on the actuator PCB located early in the stroke length at what we call the “zero” point. The sensors react when the magnet in the spindle nut passes by – thereby creating two Hall signals. The microprocessor checks for the intersection of the two magnetic fields and uses the intersection as a reference point for initialisation.

A number of PCB features help protect the machinery running with a LINAK^® industrial actuator. A pulse signal ensures the electronics are working properly, and the soft start/stop feature reduces the mechanical stress on the machinery and the actuator. This function is controlled by ramping up a PWM Motor Control signal and works in the same way as gradually releasing the clutch in a car.

Measuring current and temperature protects the PCB’s electronics and helps ensure reliable actuator performance. A microcontroller measures the current flowing through the H-bridge, and it shuts off the power if the current exceeds a predefined level. Sensors monitor both the H-bridge temperature and the ambient temperature inside the actuator housing and stop operation before the heat reaches damaging levels.

For EMC protection, the actuator PCB has a load dump functionality and a polarity protection. The load dump level for LINAK industrial actuators is predefined to 45 volts. If a voltage peak passes this level, the PCB will be shut off. Polarity protection ensures that the actuator is not damaged in case the power supply is wrongly connected.