In this article:
- Electric actuation solution for High Security Vehicle Barriers provides speed, reliability and the highest safety in all weather conditions
- Required an actuation system that can lift a heavy plate barrier designed to stop a 7.5 tonne (15,000 lb) vehicle going 80 kph (50 mph), all in 1 second
High security vehicle barriers are an application Moog has worked on for several years that presents some motion control challenges commonly faced by many industrial companies:
- Speed, reliability and safety requirements are the highest priority
- The technology is moving from hydraulic to electric
- A demanding environment requires reliable hardware and electronics
- A complete turnkey solution must be easy to implement for technicians who are knowledgeable in hydraulic technology but limited in electric servo experience
Security Barrier Application
Security is a topic frequently in the news today as countries seek to protect institutions from embassies to military installations to power facilities from potential attack. High security vehicle barriers are a last line of defense for these institutions and the technology being used for actuation is a critical factor. These barriers must be designed to stop a 7.5 tonne (15,000 lb) vehicle traveling at 80 kph (50 mph) with no penetration and need to be deployed in 1-1.5 seconds.
Until recently the technology being deployed was exclusively “open-loop” hydraulic actuation but Moog has been instrumental in helping the industry adopt a new solution with many benefits. As Moog has significant expertise in both hydraulic and servo technology we were able to evaluate all options. Some factors encouraging barrier Original Equipment Manufacturers (OEMs) to adopt electric technology included the need to accommodate demanding environmental considerations (e.g. extreme temperatures, sand, dust, rain, ice, flooding, etc), meet power requirements, ensure maximum reliability and lower maintenance costs. Ultimately Moog has helped the industry to successfully transition from open loop hydraulic to closed-loop electric realizing many desirable performance and operational benefits. This article describes this demanding application, the reasons Moog recommended electric actuation to meet the customers goals and how companies have successfully implemented this technology to achieve impressive results.
Because of terrorist threats and tactics, security barriers have become essential for an effective security program. These were initially a concept of the US Department of State (US DoS) after the Beirut truck bombing of a US military barracks in 1983 but barriers are now used worldwide. There are 3 typical types of high security barriers available today. We have all seen these in our everyday activities but may not know the technology involved. The type selected depends on the needs of the situation.
The wedge/plate barrier type uses large plates which can weigh over several thousand kilograms (several thousand pounds), requiring significant power to be raised during an Emergency Fast Operate (EFO) situation. The weight and speed requirements present many challenges to designing a motion control system.
Types of Security Barriers
Source: Courtesy of American PSG
Large steel plates which pop up out of the ground very quickly are typically deployed as final denial.
Drop Arm/Crash Beam barrier
These barriers may look fairly benign, but many have a large chain or cable inside the tubing that acts like a cheese cutter. Typically used for traffic control.
This type of barrier is more aesthetically appealing than the large plates and also allow pedestrian traffic.
To help you understand the application better it is important to explore what is required to stop a vehicle at various weights and speeds. Threat levels can be defined based on vehicle speed and weight. The vehicle bed penetration further defines the barriers stopping capability.
A vehicle moving toward a barrier has a certain kinetic energy which is the measure of how much “hitting power” it possesses. This is measured by its weight and speed. The kinetic energy changes as the square of its velocity. On impact, some of the energy is converted to heat, sound and deformation of the vehicle, the barrier must absorb the remainder. This information has been converted into standards by the Department of State, ASTM and other governmental organization shown in the table below.
Requirements from the DoS and ASTM standards
Wedge/Plate Barrier Construction Source: APSG
Penetration Measuring Location (P-Rating)
The Customer Request
Traditionally hydraulic was the technology for plate barriers as it provided adequate power to lift the heavy plates at a speed required for fast deployment. These hydraulically actuated barrier systems did not utilize servo or proportional valves or position sensing for the motion control. Valves are just opened up, the hydraulic fluid flows and the cylinder stops when it hits the end stops, or the crash arresting system also known as operating in a bang-bang mode. During the all-important EFO (Emergency Fast Operate) situation there is considerable stress put on the barrier. Typically an accumulator is provided to supply additional hydraulic fluid for EFO and power failure. Consequently the constant stress from hitting the end stops was causing premature damage to barrier components and foundation. A new solution that addresses these issues could greatly improve reliability and lower maintenance costs for OEMs.
Hydraulic Velocity Profiling
Moog needed to meet the most stringent requirements for the wedge security barrier that entail an actuation system that could lift a heavy plate barrier designed to stop a 7.5 tonne (15,000 lb) vehicle going 80 kph (50 mph) with an allowable penetration of the truck bed of less than 1 m (3 ft), all in 1 second . Customers also wanted to obtain higher reliability in demanding environments, lower maintenance costs and improve performance.
The Moog Solution
As an expert in both hydraulic and electric technologies, Moog engineers evaluated the requirements for this application and recommended applying high performance electric actuation technology that could meet the speed and force requirements but offer some other key benefits such as lower maintenance costs, less environmental concerns and high reliability. Through velocity profiling, the constant stress from hitting end stops could be prevented thereby increasing the life of the barrier, while also providing smoother operation, lower component count and the ability to handle hostile environments, all important factors for longevity of the system.
Electric Velocity Profiling
To meet the needs of the customer Moog provided the following actuation system:
- Moog Electric Servo Actuator with a unique mechanical holding brake in case power is lost
- High performance AC Servo Drive
- Application-specific software for optimizing commissioning and sizing
- Spring-assist actuator to reduce power requirement (optional)
- Barrier Control Panel with all required components for operation including noise suppression to reduce the risk of electromagnetic interference (EMI) (optional)
- Battery backup (optional)
- Actuator heating for severe weather locations
The heart of the solution is Moog’s integrated Servo Actuator and Servo Drive System with programmable control for acceleration/deceleration, speed, position and force which achieves extremely smooth, quiet operation. Since the Servo Drive controls the current into the motor, the force output of the actuator can be programmable for the specific barrier and installation, enabling optimized performance. The other major advantage is the ability to operate reliably in hostile environments such as extreme low temperatures which are accommodated by using the motor as a heater to keep the encoder compartment at a programmable temperature level. Conditions such as rain and flooding are taken care of with the actuator environmental rating of IP67. Having no oil eliminates other environmental concerns and provides smooth consistent operation regardless of temperature swings.
Moog Servo Actuators utilize high performance servo motor and ball screw technology integrated into a small high power density package with many advantages over induction motors and existing barrier hydraulic technology:
- Servo motor can be stalled at continuous torque indefinitely without damage
- Peak torque to 3X the motor’s continuous torque is available for high speed EFO
- Servo technology provides a smaller physical envelope with power densities similar to hydraulics
- Absolute encoder feedback eliminates homing requirements
- Automatic actuator heating for extreme environmental conditions
Comparison of Hydraulic and Electric Systems
Cutaway of Moog Electric Actuator
A major benefit of the electric system is the lower component count, eliminating the need for the hydraulic infrastructure and reducing maintenance costs. Other features not available with the hydraulic system are also provided such as barrier obstruction detection. Should the barrier be deployed under a vehicle a decision can be made to continue or stop. Also provided on the actuator is a holding brake which is properly sequenced via the servo drive. When the barrier is in the deployed position, the mechanical brake is applied to hold position even if power is lost. This way if the terrorist tries to defeat the barrier by removing the power source, the barrier will remain in the deployed position.
One of the challenges of this application is that barrier manufacturers are more familiar with hydraulic than electric operation and needed assistance with sizing an electric actuator for security barriers. Moog Engineers developed proprietary specific sizing software for security barriers in order to assist customers with design and optimization for operation with electric servo technology. All pertinent data is entered into the appropriate fields and a comprehensive report is generated. Important information such as power requirements and actuator life are reported allowing the barrier manufacturer to optimize the design by changing mounting locations, weight or even adding external spring assist.
Commissioning and site set-up are another critical factor on location. Moog commissioning software is designed to make this quick and easy. Specific fields are provided for normal up/down motion as well as EFO. All moves are programmable for position, speed and acceleration/deceleration. Actuator parameters are stored in the absolute encoder therefore accidental damage to the servo actuator is eliminated.Value-added Offerings for Security Barrier ApplicationsSince site power can be quite limited, Moog’s Engineering Team developed a spring assist actuator to reduce power requirements when raising a heavy plate barrier rapidly. The stored energy in the spring when the barrier is in the down position is released when the raise command is given, assisting the electric actuator and reducing power requirements. This design provides longer actuator life and reduced site power requirement for fast EFO on heavy wedge/plate barriers. Power reduction can be as much as 5X or more.
Spring assisted actuator
Moog engineers have also developed control sub-panel assemblies complete with all required components for barrier operation including noise suppression to reduce the risk of EMI interference with other equipment. Battery backup operation is also available making the sub-panel completely self-contained. A malfunction will affect only the one barrier not a group of them leaving sites more secure.
Until the last few years, hydraulic operation was the only technology with the power required to raise these large wedge/plate barriers quickly. As a technology neutral company with expertise in both hydraulic and electric technologies, Moog collaborated with barrier OEMs to evaluate all options and see what was best for this application. The result is a new solution able to deliver similar power densities as hydraulic technologies but able to provide many advantages that electric uniquely offers for this application. OEMs of high security vehicle barriers using the Moog electric servo actuation system are experiencing many advantages over existing hydraulic technology including:
- Virtually maintenance free, the electric actuator system lowers maintenance costs compared with hydraulic systems
- Velocity profiling prevents premature barrier component failure
- Emergency deployment <1.0 second (programmable)
- Wide operating temperature range with programmable actuator heating for extreme environments
- Tamper proof mechanical brake cannot be defeated assuring barrier will stay deployed
- Programmable barrier obstruction detection
- Increased power density and reliability in a self-contained ball screw design
- Ideal for new and retrofit applications
Donald Bockhahn, EMA Product Application Manager is responsible for electric actuation activity in the US market. Don has worked in electrical engineering for 30+ years, with 11 of those years designing high performance servo drives. For the last 5 years at Moog he works in a sales support role promoting and applying electric actuation technology.