Figure 1: Industrial shock absorber with Sentinel 1 monitoring system. Source: ITT EnidineFigure 1: Industrial shock absorber with Sentinel 1 monitoring system. Source: ITT EnidineTechnology advancements and the emergence of the industrial internet of things (IIoT) has led to what is referred to as Industry 4.0, or the fourth industrial revolution. Industry 4.0 combines automation with the IIoT to create smart factories, connected by the internet.

Automated factories and warehouses enable unattended operation of equipment and real-time communication of equipment status. These automation improvements, combined with the high operating speeds required to meet increasing productivity demands, have obvious advantages, but progress also comes with disadvantages. High operating speeds can also lead to an increase in noise, damage to machines, excessive vibration and accidents due to runaway equipment. If failsafe measures are not in place to detect these conditions and shut down equipment when they occur, costly accidents or personnel injuries may occur.

Controlling noise, vibration and shock due to an impact or repeated impacts is important to maximize equipment life, minimize damage and most importantly, provide a safe work environment. Products such as bumpers, springs, cylinder cushions and industrial shock absorbers are the main options design engineers employ to combat noise and vibration.

Employing industrial shock absorbers

The specific application dictates which product is optimal. Rubber bumpers and springs are inexpensive, but most of the energy at impact is stored, resulting in rebound and an undesirable recoil effect. Cylinder cushions operate over a limited operating range and provide low energy absorption, which results in shock loading and vibration.

Figure 2: Dampening options. Source: ITT EnidineFigure 2: Dampening options. Source: ITT Enidine

Industrial shock absorbers provide a controlled, predictable deceleration that converts kinetic energy to thermal energy. The shock absorber operates in the fully extended position under normal conditions. In hydraulic shock absorbers, the fluid is compressed on impact and forced through narrow orifices, which causes a rapid increase in fluid temperature that is dissipated through the cylinder body.

If it is important to limit recoil, shock and vibration, industrial shock absorbers are the clear product of choice. One such application is automated storage and retrieval systems, commonly found in modern warehouses. Large fulfillment warehouses, such as those used by Walmart, Amazon and the food industry, feature unattended stacker cranes and other automated equipment. Stacker cranes operate along the aisles of warehouses between racks or shelves. They automatically transfer products to and from the storage racks and feature both linear and vertical travel mechanisms. They position, load and extract goods to a specified rack position.

Figure 3: Stacker crane with shock absorber (lower right). Source: ITT EnidineFigure 3: Stacker crane with shock absorber (lower right). Source: ITT Enidine

Repeated soft-stop impacts are common in stacker crane operation. Industrial shock absorbers help minimize damage and dissipate the energy of the impact. While the shock absorbers can handle these soft stop impacts, repeated bumps will eventually affect the life of the unit, which will need to be refurbished or replaced.

Of greater concern are impacts due to runaway cranes or other emergency conditions, which can result in substantial damage and injury if personnel are working nearby. Shock absorbers intended for soft-stop operation absorb the impact in conditions where the velocity or impact is greater than normal. When this occurs, quickly shutting the crane down is imperative to prevent further damage or injury. In many existing warehouses, this is a manual process. Before the equipment can be shut down, somebody must notice or be made aware of the accident.

Warehouse workers have one of the most dangerous occupations with respect to on-the-job injuries, according to the U.S. Department of Labor. In addition to the obvious concern over personnel safety, there are financial costs to the company when accidents occur. According to the U.S. Department of Labor, each recordable injury costs an average of $35,000. Preventing and limiting these accidents and costs is desirable for safety, efficiency and financial reasons.

Industrial shock absorbers for Industry 4.0

ITT Enidine Inc. has been providing noise, vibration and shock solutions for industrial, aerospace, defense, rail and transportation markets throughout the world since 1966. Research and development combined with new technologies and innovation led to the development of the Sentinel 1, ITT Enidine’s first-generation, on-board monitoring system for industrial shock absorbers.

Sentinel 1 breaks new ground by integrating microelectronics into the ITT Enidine heavy-duty line of shock absorbers to provide continuous monitoring and notification of impact activity in unattended applications. The Sentinel 1 does not require any wiring or batteries and uses energy-harvesting, wireless technology to generate energy upon impact to send a wireless signal up to 2,000 ft. As the energy is generated when needed, it does not need to be stored.

Figure 4: Sentinel 1 monitoring system. Source: ITT EnidineFigure 4: Sentinel 1 monitoring system. Source: ITT Enidine

The Sentinel 1 can be integrated to a PLC or to similar plant safety controls. Depending on the application requirements, the signal can be used to either count soft-stop impacts or as a failsafe to shut down runaway equipment, preventing further damage and protecting people and goods.

Figure 6 shows a stacker crane application with multiple industrial shock absorbers. One Sentinel 1 shock absorber could be configured to count soft-stop impacts to inform maintenance personnel when the shock absorber needs replacement. A second shock absorber could notify a control system of a runaway condition. Emergency conditions such as this can shut down the crane and other systems.

Figure 5: Stacker crane application with multiple shock absorbers. Source: ITT EnidineFigure 5: Stacker crane application with multiple shock absorbers. Source: ITT Enidine

Sentinel 1 can be purchased as part of a new shock absorber or retrofit to an existing Enidine heavy-duty series unit. Replacing or retrofitting an existing shock absorber with an ITT Enidine Sentinel 1 is a simpler and more cost-effective approach than attempting to design a custom solution.


The Sentinel 1 shock absorber form ITT Enidine is a ground-breaking product that combines advanced microelectronics and wireless technology to provide continuous monitoring for industrial applications such as warehouse automated storage and retrieval systems. The Sentinel 1 can be integrated into plant predictive maintenance programs to replace shock absorbers when they have reached their end of life. Alternately, they can be integrated with plant control systems to monitor for accidents, shutting down equipment to prevent further damage or injury.

For more on the Sentinel 1, go to ITT Enidine’s website.