Machine operators and construction workers always seem to make it into the Top 10 of the Bureau of Labor Statistics’ (BLS) National Census of Fatal Occupational Injuries. OSHA estimates that workplace injuries, illnesses and deaths cost U.S. employers $170 billion annually.

BLS further notes that many fatalities result from contact with objects and equipment.  One cost-effective approach to fighting these numbers, especially where pneumatic controls are in place, is to use rod lock cylinders. These are piston-operated clamps that hold a load in position during emergency-stop (E-Stop) conditions or when an air supply might be accidentally disconnected from a system. In an E-Stop condition, all outputs go dead, and the spring-activated rod lock becomes one of the few functioning components on the machine.

Clamping, holding and ergonomics — Clamping functions are used in machine fixture and conveyor pallet applications. Rod lock cylinders serve as a toggle clamp mechanism in automated assembly lines. In one case, a conveyed pallet is automatically shuttled to each station along an assembly line. Once in position at each station, the cylinder actuates a toggle mechanism to clamp the pallet. Then, air pressure is removed from the cylinder and the rod lock. The pallet fixture is held in place by the rod lock for the machining operation.

Often, rod lock cylinders are used in welding systems. For example, a process for welding heavy structural steel I-beams with common lengths longer than eight feet originally included manual clamping and centering operations. Now, using 100-mm bore P1D rod lock cylinders, the fabricator has automated the process, reducing cycle times and improving safety.

First, I-beams are automatically pushed and held in position with air cylinders. Next, they are clamped at several different points along the I-beam by pairs of rod lock cylinders. Because welding in this application produces thermal deformation of the I-beams, which results in beam movement and poor weld quality, a consistent and high clamping force is necessary.

To accommodate this factor, air pressure is removed from the cylinder and rod lock, engaging the mechanical rod lock and keeping the I-beams exactly in place without any potential rod movement from air com­pressibility issues. After these steps are complete, using a few hand-operated air valves, welding operations can proceed.

In precision static load-holding instances, a rod lock cylinder serves as a necessary preventive measure to ensure worker safety during manufacturing. These instances include press applications to hold platen or tooling—applications in which vertical loads must remain stationary for extended periods of time, where “zero potential energy” is required (i.e., no pilot-operated check valves are allowed to trap air pressure in the cylinder), or applications where position must be maintained within 0.002 in. for extremely low backlash.

Ergonomic tooling uses cylinders as a mechanical safety measure to balance overhead tooling loads. These applications typically involve heavy or odd-shaped loads that require a manipulator to assist operators in handling the load. If air pressure is lost anywhere within the system, loads could easily fall and potentially harm workers.

In most cases, the manufacturer must take extra steps to ensure that if an E-Stop condition occurs, an external safety device is used. Incorporating this safety functionality into the rod lock cylinder simplifies the design and reduces the number of components in the system.

Rod locks provide a mechanical locking system that can hold loads indefinitely. Air, on the other hand, will eventually bleed through any seals. In the absence of an appropriate air signal, full holding force is applied to the piston rod. When a minimum of 60 PSIG air signal is present, the locking device is released. Thus, rod lock cylinders provide precise load holding capacity with virtually zero backlash and feature high accuracy for demanding, hazardous applications.