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Applications and How-Tos

AGV and Forklift Motor Brakes | Fail-safe Brake Technology

Jonathan Bullick | February 28th, 2021

Spring-set brakes used in forklifts, AGVs, and mobile robotics are extremely important as they play a critical part in the system’s safety. This post gives an overview of some considerations when selecting brakes for these machines.


AGV Robots in Warehouse Lifting Boxes
Reliable brake solutions enable AGVs to move product safely in a warehouse.


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.


A video demonstration on how Spring Applied Brakes work.
Spring Applied Brakes – See how they Work


KEB Spring applied brakes are designed for safety-critical applications. KEB brakes use multiple springs to apply 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.

KEB Brakes made in Minnesota.

Care should be taken when sizing the brakes. Will the brake be used to stop the vehicle dynamically? 

In most cases, the spring-applied brakes are not used to dynamically stop the vehicle as this leads to the 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.


Brake size

KEB brakes can produce high 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 parking (holding) or dynamic brake applications. Additionally, KEB has engineered special solutions capable of high-energy e-stops – these are used to stop AGVs with particularly large masses.


image of double rotor brake from KEB
KEB offers a wide range of brake sizes, up to 3200Nm of torque. 


IP rating

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 used outdoors or in high-humidity environments.


OEX rectification

KEB offers an OEX rectifier for a fast response. As in the example above, we want to prevent the AGV from rolling backward 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 provides both functions built into one switch. It overexcites to provide fast brake release, lowering the holding voltage, and power consumption and increasing battery life.


Image of Brake Rectifier with over excitation
Powering the brake with a reduced holding voltage will increase battery life before recharging



KEB’s COMBISTOP brakes can be equipped with a built-in hand release so that you can manually transport the AGV even without power applied.


image of KEB gearmotor brake with hand release
Hand releases are the most common brake option. They allow the brake to be released for service or to jog the machine temporarily. 


KEB’s brakes can also be fitted with an optional microswitch. Microswitches can be used in two ways. First, the microswitch can be set to close when the 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.


AGV motor brake - microswitch option
An optional microswitch can be added to the brake.


KEB – Your Brake Partner

KEB has been manufacturing spring-set brakes for 50 years. We make and assemble brakes for the North American market at our 150,000 sq. ft. facility in Minnesota. KEB’s in-house engineering department can custom-design brake solutions optimized for your application.


Contact a KEB brake engineer to discuss your application today.


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