Vertical-Axis Drives After Power Loss: Which Holding and Brake Data Must OEMs Verify?

A vertical axis holds a load against gravity. A lift, a hoist, a raised gate, or a vertical transfer can move downward if its restraint is lost. A power failure does not itself bring that load safely to rest. The OEM must establish what holds or stops it, how quickly that function becomes effective, and what movement is acceptable in the defined fault case.

A brake is only part of that answer. Holding a stationary load, stopping a moving one, and surviving a power failure are three different duties, and a drive that does one well may do another poorly. The data to confirm belongs on the OEM's desk before the machine ships. Here is what to verify, and the boundary around what a brake or a gearbox can be trusted to do.

What Happens to a Vertical Axis When Power Is Lost

When motor torque is lost, an unrestrained gravity load can drive the axis downward. The timing depends on the actual drive and power architecture: mains loss, loss of control power, and torque disable are not necessarily the same event. Stored energy or a backup supply may support a controlled stop only if that behavior is designed and verified.

The safety question is which restraint remains effective in the particular failure case. It may differ from the motor torque or mechanical support used during normal operation. Trace the load path from the suspended mass through the transmission, brake, and supporting structure. A motor-mounted brake cannot hold a load through a failed downstream coupling or shaft. Assess the fault case separately, using the actual arrangement.

Define the Four Duties Separately

The first step is to stop treating "the brake" as one thing and name the four duties the machine actually needs.

• Static holding: keeping a stationary load from moving, with no rotation, over a long time and through a power loss.
• Dynamic stopping: bringing a moving load to rest, accounting for kinetic energy and the work done by gravity during the stop.
• Normal stop: the routine stop at the end of a cycle, which may use the drive, the brake, or both.
• Fault condition: what happens on power loss, an emergency stop, or a component failure, where the required behavior is set by risk assessment.

These are different requirements, and a single brake rating does not cover all four. A brake that is excellent at static holding may be unsuitable for repeated dynamic stopping, and a brake rated for dynamic stopping may not hold the load statically to the torque the application assumes.

Verify the Brake's Holding Torque and Its Conditions

When a manufacturer publishes a holding or static torque for a brake, that figure comes with conditions, and the conditions are where mistakes hide.

First, distinguish static holding torque from dynamic braking torque. Obtain the minimum applicable holding torque, its tolerance, and its temperature, wear, and environmental conditions; do not treat an unexplained nominal value as a guaranteed minimum. Confirm any manufacturer-required conditioning or inspection. Separately obtain the permitted dynamic duty if stopping a moving load is required.

Second, verify release and engagement behavior. An electrically released, spring-applied brake is designed to apply as coil excitation is removed, but its holding torque is not established instantly. Confirm command delay and torque build-up time with the specified supply and switching circuit. Also verify release timing and the overlap with restored motor torque. The description "spring-applied" alone does not establish a complete machine safety function.

Third, verify dynamic limits: permissible engagement speed, braking torque, energy per stop, total wear allowance, and stopping frequency. Some holding brakes permit a limited emergency-stop duty; others do not permit the proposed duty. For a descending load, include gravity's work as well as kinetic energy and any motion before the brake engages. Check the resulting torque, stopping distance, energy, and thermal duty against the selected brake's data.

Verify the Controller and Brake Sequence

Holding torque is only as good as the sequence that applies it. The controller, the motor, and the brake have to be treated as one system with a defined timing.

Ask for the complete timing: motor torque availability, brake command, actual holding-torque establishment, feedback, and power availability to each control element. During a normal controlled stop, the drive may hold the load until the brake has engaged. An abrupt supply failure may prevent that sequence from completing. Evaluate each specified fault separately and determine what restrains the load throughout the handover.

Validation belongs to qualified personnel under a written test plan with an independently secured load and controlled access to the hazard area. Do not demonstrate the sequence by simply cutting power to an unprotected suspended load. The test and any temporary restraint must be designed for the machine; a brake-command signal alone is not proof that holding torque was achieved.

Assess the Whole Machine and Its Failure Cases

The required holding and stopping functions, their fault tolerance, and the need for independent restraint or monitoring come from the machine risk assessment and applicable requirements. A brake datasheet alone cannot settle them.

Some arrangements use a brake as the primary restraint; others require an additional holding path. Check whether the proposed backup actually remains effective for the failures being considered, including shared shafts, couplings, power supplies, or controls. Two components are not necessarily independent just because both can hold a load.

Do not treat a worm gearbox's nominal self-locking behavior as proof of a safety function. Its backdriving behavior must be confirmed for the actual configuration and operating conditions. For example, SEW-EURODRIVE's self-locking guidance explicitly excludes the self-locking effect as the sole safety function for hoists. Any safety-related holding arrangement needs the appropriate system design and validation; a ratio or a "self-locking" label is not sufficient evidence.

What to Collect for the Holding and Brake Review

FAQ

Can a holding brake always be used to stop a moving load? No. Static holding torque does not establish permissible stopping torque or energy. Some holding brakes have a defined limited emergency-stop capability, which must be checked against speed, load, energy, and number of stops. Obtain that confirmation for the selected brake rather than assuming either unlimited dynamic use or no dynamic capability at all.

Can a self-locking worm gear replace a load-holding brake? The label alone cannot justify removing a required brake or restraint. Confirm the actual backdriving behavior and the complete safety-related holding function, including relevant faults. Use the machine risk assessment and the manufacturer's restrictions to determine the arrangement; do not infer a power-loss safety guarantee from gearbox ratio.

Technical References

Kollmorgen’s AKD brake-timing note, Rev. B, illustrates the difference between controlled stopping and torque removal. Its parameter settings apply to that system. Mayr’s brake-system overview distinguishes holding applications from dynamic braking capability that depends on the brake design. These references explain why timing and duty require separate checks; they do not establish ratings or safety performance for a Mingye configuration.

Next Step

If you are specifying a vertical-axis drive and want the holding and brake data checked before the machine ships, send us the load and gravity case, the duty definitions, the brake data, and the control sequence. Ask us to review the drive configuration and identify the component data still needed. Final machine safety validation remains part of the OEM's system review. Explore our material handling system solutions, or contact us to start a configuration review.