Overview
SOMANET Circulo includes an Integrated Brake System that prevents motors from unwanted rotary motion.
It is designed as a spring-applied brake; in case of a power loss, the integrated brake locks the motor.
The integrated brake system is available with - or without - a torque limiter, and is advantageous when used inside robot arms and in mobile robots.
Brake System Components
The integrated brake system includes the following components:
-
a solenoid actuator,
-
a notched wheel, and
-
a torque limiter.
Figure 1 - Integrated brake system with the torque limiter
Solenoid Actuator
The linear solenoid consists of a helical coil with a ferro-magnetic actuator or “plunger”, called an anchor, which converts electrical current to mechanical force.
The solenoid actuator is specifically designed for locking rotary motors. When energized, the lock remains retracted and the motor can turn. When de-energized, locking occurs.
Figure 2 - Solenoid actuator (cut view simplified)
Figure 3 - De-energized and energized solenoid actuator (side view)
| Solenoid Actuator Technical Specifications | |
|---|---|
|
Pull Voltage |
43 V |
|
Hold Voltage |
9 V |
|
Recommended pull time (@ 43 V) |
50 ms |
|
Max. pull time (@ 43 V) |
200 ms |
|
Duty cycle |
43 VDC : S3 (1% ED) 9 VDC : S1 (100% ED) |
|
Power Consumption |
3 W @ 9 V |
|
Coil winding |
Thermal class B (130 °C) |
|
Stroke |
3.5 mm |
|
Anchor Latching Time |
Solenoid delay* : 20 ms Movement duration: 4 ms |
|
Maximum Lateral Force on Anchor (at 2/3 of its extended length) |
1000 N |
|
Cable Specification |
2 x AWG26 UL Style 10125 |
|
Connector |
JST SZE-002T-P03 |
|
Connector Housing |
JST ZER-02V-S |
|
Anchor Weight |
9 g ± 10% |
|
Total Weight |
40 g ± 10% |
|
Storage and Transport Temperature |
-5 °C to 70 °C |
|
Ambient operating temperature |
+5 °C to 70 °C |
|
Corrosion Resistance |
Cr(VI)-free according to ISO 19598:2016 |
|
B10d opening/closing cycles |
1,000,000 |
* Time required to discharge the solenoid. The anchor will start to move 20 ms after the voltage is removed.
Permitted Duty Cycle
The permitted duty cycle is explained in the formula below, where Ts represents the time between 2 pulls in seconds, and Tp represents the actual pull time in seconds.
Duty Cycle:
Figure 4 - Duty cycle
Duty cycle example: Ts = 0,05 * 60 = 3 s
Notched Wheel
The notched wheel is connected to the motor shaft and rotates relative to it. This connection is made using a frictional connection (when using a torque limiter) or a form lock (when no torque limiter is used).
Figure 5 - Notched wheel designations
When de-energized, the solenoid actuator’s anchor:
-
drops down,
-
stops the notched wheel,
-
receives the force of an impact, and
-
prevents unwanted rotational movement between the anchor and the notched wheel.
The anchor also determines the backlash and maximum locking angle at the robot’s end effector. Even with a high reduction gear ratio, this is not negligible.
Figure 6 - Notched wheel engaged on the solenoid actuator
Note: Other notched wheel styles are possible; refer to the following example.
Figure 7 - Example of the notched wheel geometry, which is connected to the motor shaft
Torque Limiter
The energy generated by a robot’s movement must be absorbed somewhere when a stop occurs. When using a solenoid actuator with a torque limiter, the torque limiter absorbs the energy through friction, thereby limiting any potential damage to the components.
Attention: When not using a torque limiter and a"Stop Category 0" occurs, energy cannot be absorbed and severe structural and/or component damage may occur.
Figure 8 - System overview and working principle
The Quick Stop Function
The servo drive’s integrated quick stop function can be configured so that the motor speed is reduced to a low level before the brake latches. This is useful when an unexpected fault occurs, for example, a communication error or power loss.
For additional information on the quick stop function, refer to Quick stop .
If configured correctly, when a power loss occurs while in motion, the quick stop function - triggered by the undervoltage protection - prevents a hard stop. Refer to Protection for additional information.
Note: The undervoltage setpoint variable should be set below the nominal supply voltage.
For example, it should be set at 48 V supply voltage:
undervoltage_setpoint = 48 V - 5 V = 43 V.