Application scenarios of safety function options of servo controllers

With the advancement and vigorous development of the concept of Industry 4.0, machines and equipment assist or replace personnel to complete product production and processing processes more efficiently and accurately. At the same time, high-speed moving parts on machines and equipment may cause varying degrees of harm to operators. Countries and regions around the world will formulate corresponding safety production regulations and standards to ensure that all machine manufacturers are aware that machines must meet strict safety requirements to protect workers from harm.

As an important part of modern equipment, servo motors, in conjunction with the different safety functions of servo controllers (servo amplifiers), can keep the machine running normally while providing safety protection for operators, which will greatly reduce people's impulse to bypass safety function facilities and "run red lights". Many operations that previously required shutdown and restart can now be completed while the machine continues to produce at a reduced speed or even at full speed. Functional safety not only ensures the safety of the operator, but also maximizes machine productivity. In actual use, servo controllers can provide more safety function options in addition to the STO safety function. Next, we will select several to explain in detail and illustrate the actual application scenarios.

1. Safe torque off

The safety function "STO" will cut off the power supply to the motor from within the servo control, and the motor will be in an uncontrolled stop state, which complies with the stop category 0 in the standard EN 60204-1. Application scenario: After the STO safety function is activated, the motor is in a torque-free state and no dangerous movement will occur. It is suitable for urban scenes and equipment where the motor can be stopped or reduced to a speed range that will not cause danger in a short time after the safety function (emergency stop, safety door) is triggered. However, if the motor falls due to the gravity of the component itself when it moves vertically, a brake mechanism needs to be added to prevent personal injury caused by gravity fall.

2. Safe stop 1

Safety function "SS1" brakes the motor in a controlled manner, monitors the motor's deceleration within a specified range, and activates the STO function to cut off the motor power supply after a certain delay or when the speed threshold is reached. The motor is in a controlled stop state, which complies with the stop category 1 in standard EN 60204-1.

Application scenario: After the SS1 safety function is activated, the motor is in a controlled stop or deceleration before entering the STO state to avoid dangerous movement. It is suitable for when the safety function (emergency stop, safety door) is triggered, the motor cannot be stationary in a short time (high speed or large component inertia) or to avoid the process being incomplete, resulting in product scrapping or additional risks. However, the surrounding safety protection devices need to have a delayed opening function, such as the safety door switch needs to have a locking function. After the door opening request is issued, the controller can first send a stop signal to the servo controller. After the motor enters the STO state, the safety door switch can be unlocked to enter the dangerous area.

3. Safe operating stop

The safety function "SOS" is used to monitor the motor's stationary state. The motor can maintain torque output and be stationary, rather than using an external brake (such as a brake) to achieve stationary state. Application scenario: After the SOS safety function is activated, the motor will be in a controlled stationary state. It is suitable for situations where the motor needs to be stationary and the power supply cannot be cut off after the safety function (emergency stop, safety door) is triggered.

4. Safe stop 2

The safety function "SS2" performs controlled braking on the motor, monitors the motor's deceleration within the specified range, stops the motor, and then activates the SOS function to monitor the motor's static state. The motor is in a controlled stop state and the power source is disconnected, which complies with the stop category 2 in the standard EN 60204-1. Application scenario: After the SS2 safety function is activated, the motor will stop in a controlled manner and monitor the static state. It is suitable for when the safety function (emergency stop, safety door) is triggered and the motor needs to be in a static state after a controlled stop and the power supply cannot be cut off.

5. Safe limited speed

The safety function "SLS" prevents the motor from exceeding the set speed limit. Application scenario: After the SLS safety function is activated, the motor is not allowed to run above the speed value set by the servo controller. It is suitable for certain situations (such as manual or maintenance mode) when the safety function (safety door) is triggered and personnel must enter the danger zone to use the enable button to operate the moving parts at a low speed.

6. Safe direction The safety function " SDI " prevents the motor from moving in the wrong direction. Application scenario: After the SDI safety function is activated, the motor is only allowed to move in the set direction. Applicable in specific situations (such as manual or maintenance mode), when the safety function (safety door, light curtain) is triggered, the motor can only move in the safe direction (away from the operator).

Functional safety is an approach to ensuring safe machine operation that does not forcibly separate the operator from machine motion control, but allows safe interaction between the operator and machine motion even when powered on. It can also help achieve continuous operation within safety limits and thus improve productivity.