Limit switches have boundless applications in managing crane activity to prevent potential occurrences. For example, when ropes emerge from the groove or in keeping two trolleys from impacting on the same bridge structure.

Moreover, a limit switch keeps a crane from lifting loads above the appraised limit. Another type of limit switch keeps the hoist from reaching the upper block and rope drum. Then, the other type protects the engines from overheating.

Without overhead crane limit switches, the potential for harm is very high. Thus, the operator should inspect and maintain each limit switch regularly.

Check limit switches regularly.

As they open or close electrical circuits, limit switches wear out over the long run. To monitor wear and replace switches before they come up short, the operators should check the limit switches regularly before using the crane.

Konecranes has led extensive research to determine the number of uses a limit switch can perform. This gives fundamental data for creating inspection and maintenance programs.

Know how a limit switch works

Knowing how a limit switch functions is significant for understanding how the crane functions and how these setpoints keep the crane working securely and productively.

Now and again, there might be various limit switches related to crane activity, for example, crane travel or lift movement. The first switch will signal that the end of the safe travel limit is approaching and slows the crane’s motion. A subsequent switch will demonstrate that the end of the safe travel distance has been reached and stops the motion.

Lifting movements might be served by a few limit switches, which give set points for safety and reliability. For example, an initial limit switch will slow the hoist before it arrives at the stop limit. Slowing the hoist before reaching the limit decreases mechanical wear, as the hoist is going below the maximum speed when the breaks are set.

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

The ultimate limit

An extra limit beyond the stop limit- customarily called the “ultimate limit” prevents the hoist block from impacting the drum. The ultimate limit acts as a shield when the stop limit fails or the operator set it inappropriately.

This additional limit prevents two-blocking- that is, when the hook block contacts the drum hoisting machinery. Two-blocking is perhaps the most hazardous incident involving cranes, as it can snap wire ropes and cause dropping loads and other horrendous mishaps.

After tripping, the ultimate limit might require a manual reset. This includes resetting a wedge part or level so the operators can do an inspection to determine why the crane reached this position and didn’t stop at the up-stop-limit position.

Limit switches can likewise be efficient for travel motions, giving consistent and predictable movement limits without impact at end stops. In automated environments, lasers or encoders track the positions of crane movements. It also restricts switches to provide consistent calibration points to ensure values are accurate for safety and reliable production.

Limit switches role in cranes
Photo credits to Massachusetts Contractors Academy

Source: Konecranes