A technician inspects the overhead crane.
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The role of the limit switch in promoting overhead crane safety

A limit switch is a critical component of overhead crane safety. Limit switches are electromechanical devices that regulate everything from household appliances to industrial machinery. For an overhead crane, they provide solid, established points of reference for maintaining efficiency, reliability and safety standards.

 

By Casey Storer

 

Limit switches have practically limitless applications in regulating crane operation to prevent potential incidents. For instance, when ropes come out of groove or in preventing two trolleys from impacting on the same bridge structure.

In addition, a limit switch keeps a crane from lifting loads above rated capacity. Another kind of limit switch prevents a hoist from reaching the upper block and rope drum. Yet another type protects motors from overheating.

Without overhead crane limit switches, the potential for harm is quite high. For this reason, each limit switch should be inspected and maintained regularly.

 

Check limit switches daily

As they open or close electrical circuits, limit switches wear out over time. To monitor wear and replace switches before they fail, limit switches should be checked daily before a crane is used.

Konecranes has conducted extensive research to determine how many uses a limit switch is physically capable of performing. This provides essential information for developing inspection and maintenance programs.

 

Know how a limit switch works

Knowing how a limit switch works is important for understanding how the crane works and how these established set points keep the crane operating safely and efficiently.

In some cases, there may be multiple limit switches associated with a crane operation such as crane travel or hoist motion. The first switch will signal that the end of the safe travel limit is approaching and slows the crane motion. A subsequent switch will indicate that the end of the safe travel distance has been reached and stops the motion.

Hoisting motions may be served by several limit switches, which provide set points for safety and reliability. An initial limit switch will slow the hoist before it reaches the stop limitation. Slowing the hoist prior to reaching the limit decreases mechanical wear, as the hoist is traveling below maximum speed when the brakes set.

The “up” stop limit switch provides a safe position for the hoist to stop motion for safe travel motions and standby positions.

 

The ultimate limit

An additional limit beyond the stop limit—typically called the “ultimate limit”—prevents the hoist block from impacting the drum. The ultimate limit acts as a safeguard in the event the stop limit fails or is set improperly.

This extra limit prevents two-blocking—that is, when the hook block contacts the drum hoisting machinery. Two-blocking is one of the most dangerous incidents involving cranes, as it can snap wire ropes and cause dropped loads and other catastrophic accidents.

After being tripped, the ultimate limit may require a manual reset. This involves resetting a wedge component or lever so that an inspection can be carried out to determine why the crane reached this position and did not stop at the up stop limit position.

Limit switches can also be used for travel motions, providing consistent and predictable motion limitations without impact at end stops. In automated environments, lasers or encoders track positions of crane movements, and limit switches provide consistent calibration points to insure values being used are accurate for safety and reliable production.

Konecranes uses limit switches to calibrate Sway Control height and other critical measures of repeated accuracy to control real-world position.

More information about limit switches

Konecranes STORE for crane parts

Konecranes parts

Buy parts, including limit switches, on Konecranes STORE. You can find parts for many brands, makes and models of cranes and hoists as well as selected pre-configured lifting equipment.

Go to the STORE

CheckApp for Daily Inspections

Daily inspection a safety must

The daily inspection is a user’s – or crane operator’s – own assessment of the condition of an asset and environment for safe use. Checking that the limit switches work normally is part of a daily inspection. Konecranes CheckApp helps users quickly and easily record their findings when performing these inspections.

Learn more about CheckApp for Daily Inspections

Remote monitoring for overhead cranes

Remote Monitoring for crane usage and operating information

TRUCONNECT Remote Monitoring collects condition, usage and operating data from control systems and sensors on a crane and provides alerts of certain anomalies.  Operating statistics, such as emergency stops, can indicate that the hoist is being operated to the limit switch and that operator training is needed.

Learn more about Remote Monitoring

Konecranes technician servicing crane

Preventive maintenance program

The Konecranes CARE Preventive/Predictive Maintenance program includes MAINMAN Planned Maintenance which includes limit switch inspections and adjustments.

Learn more about the CARE program