Spring-set brakes used in forklifts, AGVs, and mobile robotics are extremely important as they play a critical part in the safety of the system. This post gives an overview of some of the considerations when selecting brakes for these machines.
AGV motor brake solutions: Why fail-safe brakes?
A “Power-off” brake is often specified since the brake engages in the case of loss of power. In this scenario, there is usually a loss of control and the safe handling is to stop the machine as quickly as possible. Brakes are typically integrated into the motor or wheel and directly stop the rotation of the shafts wheel.
KEB Spring applied brakes are designed for safety-critical applications. KEB brakes use multiple springs to apply a force on the armature. Even if one of the springs were to collapse on itself, the brake will still develop significant torque. The scenario of a spring failing is quite low as the springs KEB uses are rated for 10M+ cycles which far exceeds the requirements of most applications.
Care should be taken when sizing the brakes. Will the brake be used to dynamically stop the vehicle? In most cases, the spring-applied brakes are not used to dynamically stop the vehicle as this leads to wearing of the friction lining and eventual maintenance or brake replacement. With the advancement of motors and controls, a more common topology is to use the motor controller to stop and the excess energy can be returned to the battery. In this case, the brake is mainly used as a holding brake with the capability of an e-stop.
KEB brakes have the capability of producing a high amount of torque in a relatively small physical package. This way they can fit on even small applications. KEB spring-set brakes can be engineered and selected for both parking (holding) or dynamic brake applications. Additionally, KEB has engineered special solutions that are capable of high-energy e-stops – these are used to stop AGVs with particularly large masses.
KEB is capable of creating a brake with up to an IP65 rating. This means that they can handle high humidity and dust infiltration. This will be particularly interesting for machines that are used outdoors or in high humidity environments.
KEB offers an OEX rectifier for a fast response. As in the example listed above, we would like to prevent the AGV from rolling backward at all and gaining momentum. Simple physics says that something with a lot of inertia is harder to stop. So the faster switching times we can obtain, the better. OEX rectification also reduces power consumption and reduces heat generation.
KEB’s 24V powerbox actually provides both functions built into one switch. It overexcites to provide fast brake release, but then lowers the holding voltage which lowers power consumption and increases battery life.
KEB’s COMBISTOP brakes can be equipped with a built-in hand release so that you could manually transport the AGV even without power applied.
KEB’s brakes can also be fitted with an optional microswitch. Microswitches can be used in two ways. First, the microswitch can be set so that it closes when brake engages. This gives the controller confirmation that power can be cut to the motor. Secondly, the microswitch can be used as a wear indicator for the friction lining. The switch will open, indicating that the brake should be proactively serviced before the airgap becomes too large and the brake stops operating.
KEB – Your Brake Partner
KEB has been manufacturing spring-set brakes for 50 years. We make brakes for the North American market at our 150,000 sq. ft. facility outside Minneapolis, MN. KEB’s in-house engineering department can custom design brake solutions that are optimized for your application.
Contact a KEB brake engineer to discuss your application today.
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