How sensors in gate motors have made gate automation safer?

EU safety regulations allow me to open a gate because I am sentient, that is to say I am able to perceive or feel things.

As gate motors become more sentient, they will become safer. I am trusted because a can assess the risks of the opening of the gate, I can feel any gate’s inertia, and can estimate the point at which I can decelerate the gate to safe stand still. So what of these sentient processes are not available to modern
gate technology?

Any sensible human would start by grabbing the end of the gate. It suits our ‘gearing’ which is low power with sensitive feedback. A motor has to turn the gate from the hinge end. Easy enough for a geared motor, but requires accurate force sensing. A motorised wheel would better simulate the human
experience and potentially be more sensitive.

Our ability to control the progress of the gate movement is attributed to our sense of touch, known as ‘haptics’. Robots can be used for sensitive tasks like picking a ripe strawberry when they are equipped with haptic sensors. Good visual processing already endows the ‘Dyson Farming’s’ pickers to
identify the best fruit through colour and shape. Haptics can tell if the fruit is too soft, potentially too ripe.

POWER MEASUREMENT
A gate control panel measures the power used by a motor by measuring current and voltage. Hall effect sensors are more accurate and resilient than resistors. However, for reasons of geometry, the relationship between motor power consumed and a swing gate’s force is neither predictable nor linear.

Motor power can be measured during a calibration cycle of the gate, creating a force against position graph. Force mapping is common place in garage door openers. Load figures should be updated dynamically to allow for aging. The controller needs to know the gate or door position to apply the correct force
limit.

POSITION MEASUREMENT
An incremental encoder is like a pedometer that counts paces. Incremental encoders count motor rotation but can’t tell gate position. An absolute encoder knows the exact gate position like a weathervane. Control panels zero the position counter when the gate is closed, then count up as the gate opens. If
the gate motor is manually released, of the power switched off, the count no longer relates to gate position. Control panels re-find the closed datum point while running at a safe slow speed. FAAC’s ‘safecoder’ is an absolute encoder option on some control boards. The technology is based uses a fixed magnet and a 2 axis magnetometer.

Incremental encoders can be optical or magnetic. Accuracy depends on motor speed and gearing. Brushless motors use internal magnetic sensors for timing, which can also be used for gate position. Because BLDC’s are highly geared, counts are much higher resulting in greater positional accuracy beyond
practical requirements.

DYNAMICS FORCES
The force applied by a gate is the addition of motor power and kinetic energy (weight x speed). This sum of 2 forces is predictable, but only if the controller knows the weight and length of the gate. However, wind buffeting on boarded gates is an unknown force, and so is the resonant whipping that happens with long light gates.

A human would feel both forces and compensate. A gate can be fitted with an accelerometer to detect the random forces, then slow the gate down to reduce the risk of un-controlled energy swings. A more complicated solution would be to use the accelerometer within a feedback loop. Motor force would be used to reverse each random force.

Conclusions. Marketing would have our customers believe that control and monitoring makes the gate safety compliant. Force and position monitoring helps the controller repeat a safer gate movement but does not replace force testing and safety devices like photobeams and sensitive edges, the only
reliable optics and haptics. Those ghastly looking motorised wheels are probably the safest automation starting point.