Ideal control systems

Published:  08 September, 2017

Forklift trucks need fast and easy access to and from premises, taking goods and pallets out to, or bringing them in from, delivery vehicles. Maximum transport efficiency would be afforded simply by a hole in the wall; but of course there are security considerations and the need to prevent heat/cold transfer. Naturally, then, there are doors, and for every door there is an ideal door control system. Paul Rudge of sara LBS examines the various choices, and highlights the advantages, disadvantages and installation requirements for each.

The choice of door control system has a big impact on the operational efficiency of a factory, warehouse or distribution centre. There are a number of options to consider, each with their own advantages and disadvantages, as well as implications for installation.

The simplest option is a push button station, with one push button installed on the front panel of the control box and a second push button fitted to the other side of the wall. Easy to install and easy to understand, the simplicity of the push button solution is its biggest advantage. It is also useful for enabling maintenance checks on doors. For added security, a key switch can be added.

Of course, from an efficiency point of view, there are disadvantages. The driver has to stop his fork lift in front of the vehicle, dismount, walk to the wall and press the button to open the door, and then get back into the truck before driving through. That can take upwards of 30 seconds, and increasingly it is marginal gains that companies make that really drive up production efficiency. There is also the temptation for other personnel to make use of the forklift door to enter and exit the building, rather than the separate personnel door. That can have implications for environmental management and health and safety protocall.

In weighing up the advantages and disadvantages, the installation requirements for any door control system also need to be considered. The push button solution is certainly a simple installation option and it operates off the standard mains power supply.

A step up from the push button switch option in terms of productivity and efficiency is the pull switch, fixed to the ceiling ahead of the door, both in front and behind. As with the push button, it is simple to install, operating using just the mains power supply, and is easily understood. As the forklift approaches the door, the driver slows down and pulls the cord, activating the door. Because the driver has to reduce speed or even pause, it could be said that the pull switch option promotes safety and good discipline. Additionally there is no need for the driver to dismount the vehicle and walk to a wall mounted switch, so there is a tangible increase in operating efficiency. There is, however, a slight risk of the suspended cord being caught by passing vehicles.

A more sophisticated driver-activated door opening control is the remote transmitter, usually either radio or infrared. With a receiver mounted in the control box and the transmitter either hand-held or mounted in the cab, there is no external wiring so installation is simplified. However, the receiver needs a 24V supply and the transmitter needs a 9V battery. The door can only be activated by authorised personnel, and the system promotes good driver discipline, with the driver having to make a conscious decision to activate the transmitter.

The driver, however, does have to activate the transmitter early enough for the door to open before the fork truck reaches it, or there is a risk of collision. That distance needs to be thoroughly tested, because occasionally the range or sensitivity of the system can be affected in buildings where large amounts of steel framework are present.

Addressing security concerns, over 1000 pre-set combinations are possible, and the systems are coded so that a given transmitter only opens a given door and no others.

Fully automated opening

For maximum operational efficiency and prevention of possible accidents, businesses can consider fully automated doors; with options for detection of the fork lift being inductive loops, photocells or radar detectors.

Of these, radar offers the simplest installation, with a detector located above the door on either side of the wall – safely out of the way of passing vehicles so not at risk of mechanical damage – and needing only a 24V DC power supply. With a typical angle of detection of 20° from the vertical, the detection area extends around 2.5m from the door, which opens as the fork lift truck enters that area. The driver doesn’t have to remember to activate the door manually, but this advantage is offset in some installations by the fact that the system is not selective – anything or anyone that passes through the detection zone will cause the door to open.

Another option for automatic opening is a detection solution built around photocells. A send/return unit is mounted to the left or right of the door, with a reflector the other side, and as the fork truck breaks the beam of light between them, the door is triggered to open.

Mounting flexibility is assured by a range of up to 15m depending on the model selected, but users must ensure that the mounting height is suitable for all types of truck that will be using the door. And of course, there must be something convenient to mount the devices on.

In environments where these requirements are addressed, the photocell option offers one of the safest and most efficient solutions. While, as with other control options, the door can be set to close automatically after a set time period (generally any time up to 30 seconds), the photocell solution will hold the door open all the time the beam is broken, and will not start the timing procedure to close the door until the obstacle has cleared the beam. Also, as the fail safe, the door will open and remain open should a fault arise with the photocell, perhaps through mechanical damage.

A final option to consider is the inductive loop. Here a continuous wire loop runs through a groove cut in the floor, extending to an area wide enough to give the door time to open as the fork truck approaches. As a rule of thumb, that distance should be roughly equal to the height of the door, but sensitivity may be reduced if steel material (such as floor reinforcement, pips or drains) is within 500mm of the loop.

Buried within the floor, the inductive loop solution is free from the risk of mechanical damage, but this has to be balanced against the more challenging installation requirements, with the loop having to sit within a channel cut in the floor some 20mm deep and 5mmwide.

Because it is sensitive to metal, the inductive loop will only detect the presence of the fork truck, and not personnel who happen to wander into the detection area. Depending on the application, that might be considered an advantage or disadvantage.

We can see, then, that there are many different options for controlled opening and closing of doors for forklift truck access, each with its own advantages and disadvantages. Ultimate choice will depend on assessment of a number of different key performance indicators, including the need to control thermal transfer, the impact on operational efficiency, the structure of the building and safety. A knowledgeable supplier such as sara LBS will always be able to advise on the best solution for any given applications.

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