Rocker vs Rotary Cam Limit Switches

In order to specify mechanical limit switches successfully and avoid premature failure, it is important to select the appropriate actuation method for your application. In the article, we will explain the 2 main types of mechanical limit switches, how they operate and wat to consider when selecting for your application.

Types of Industrial Limit Switches

There are several categories or classifications of industrial limit switches on the market. The most common types of limit switches are mechanical limit switches, non-contact proximity switches, and photoelectric switches. Mechanical limit switches are suitable for the vast majority of applications and are generally the most economical to use. Therefore, the mechanical limit switch is typically the first choice.

How Does a Mechanical Limit Switch Work?

Mechanical limit switches operate based on two types of working principle, the cam-type, and the rocker-type. In a rotary cam limit switch, a cam engages the limit switch lever or plunger, which makes or breaks an electrical contact inside the limit switch. In a rocker-type limit switch, rotation of the external lever shaft and lever shaft assembly causes the rocker to pivot, shifting and locking the latches.

It is essential to learn more about how rocker-type and rotary cam limit switches operate and which suits your application best. Experience has shown that most industrial limit switch failures occur due to faulty installation. In some cases, a perfect installation is not possible, but in the majority of cases, proper application of the limit switch would have prevented failure.

What is a Rotary Cam Limit Switch?

In a rotary cam limit switch, rotation of the lever shaft and cam assembly drives the cam follower/shuttle assembly. The assembly then pushes the operating pin, allowing one set of latches to release the initial position of the shuttle and the other set of latches to hold the shuttle in the moved position. Movement of the shuttle also transfers the contact position in a snapping motion, which makes or breaks an electrical contact inside the limit switch. This electrical control signal limits the position or reverses the machine travel to initiate another operating sequence. It can also be used for counting, sorting, or as a safety device.

Removal of the operating force allows the return spring to move the cam follower/shuttle assembly and contacts to the initial position. Latches are then reset to the initial position at this point.

What is a Rocker-type Limit Switch?

In a rocker-type limit switch, rotation of the external lever shaft and lever shaft assembly causes the rocker to pivot, shifting and locking the latches. The movement of the rocker also transfers the contact position in a snapping motion. Removal of operating force allows the return spring to pivot the lever shaft assembly, which returns the rocker and contacts to the initial position in a snapping motion. At this point, latches reset.

The cam-type and rocker-type limit switch differ in operation to account for a difference in application. The cam-type limit switch offers low trip torque, longer total actuator lever travel, and it can deliver three normally open and three normally closed contact arrangements. This limit switch performs best in applications such as bi-directional movement, overtravel protection, door open and closure, and mobile equipment. The rocker-type limit switch offers higher trip torque, shorter total actuator lever travel, and can have a reverse shaft. Unlike cam, rocker-type limit switches operate in one direction with short travel for applications like valve position indication and presence detection.

What is SNAP-LOCK® Technology?

Both cam type and rocker type limits switches use quick make or break action to open or close a circuit to indicate position. Namco enhances these mechanisms with SNAP-LOCK® technology. The SNAP-LOCK® action ensures a quick make and quick break of contacts together with mechanical locking in either open or closed positions.

Mechanical Limit Switch Mechanisms

Important Actuator Considerations

The most important consideration in the proper application of limit switches is external cam design, as the majority of limit switch failures can be traced back to poor cam design. Excessive over-travel and/or excessive snap back of the operating lever arm are the most common abuses. A good cam design will greatly increase the life of your limit switch.

Listed below are general rules for the proper design and application of limit switch cams published by NEMA in Standards Publication ICS2-225.

Learn More about Recommended Current Ratings for Mechanical Limit Switches Here

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