Silverteam and Frontier Pitts develop Terragate

Edited by the Engineeringtalk editorial team Sep 25, 2008

Silverteam has revealed how it worked with Frontier Pitts to develop the Terragate, a heavy duty gate capable of sliding shut in seconds.

Frontier Pitts offers a number of basic gate designs, but each has to be customised to meet the exact needs of the location.

Often, because of space restrictions, a sliding gate is required, and these may have to be 4-5m wide to allow lorries to pass.

There are several options for the opening and closing mechanism, but Neil Fairchild, the engineer behind the Terragate, prefers a chain and sprocket drive because of the simplicity and reliability.

This has to be motor driven, and in these days of rising energy costs and increasing environmental awareness, he likes to make sure the motor is not oversized yet is powerful enough to cope day in and day out.

It took several years from the 9/11 attacks to formalise long-term reliability, operational health and safety, performance parameters, and so on into internationally acceptable standards.

Once the standard was agreed (European Has68 and US K12) and Frontier Pitts called in motion experts from Silverteam to begin working on a suitable drive system.

Two operating patterns were needed, regular and emergency.

The first uses gentle acceleration and deceleration to avoid unnecessary stress on the drive system, gate and supporting structure.

Maximum speed attained in a typical installation would be 500mm/s, giving a closing time of 10-15s.

For the emergency pattern, the idea is to shut the gate a quickly as possible, accepting shock loads to the system and assuming the structure can withstand the impact stresses.

Here the drive is used to generate maximum acceleration and the gate is allowed to slam shut against a 'faceage' a rubber strip type shock absorber.

Typically the gate will reach a speed of 1,000mm/s or more, meaning that even the widest gate will be secure within seconds.

Silverteam assessed the two patterns and considering the shock loads, the harsh outdoor environment of most applications and the need for long-term reliability, suggested a Hitachi SJ 300 variable drive coupled to a Bauer geared motor.

The SJ 300's abilities to cope with large loads at high speeds and accelerations made it ideal for the Terragate.

It uses Hitachi's Advanced Sensorless Vector Control, which offers 200 per cent starting torque and full torque at 0Hz without feedback.

For the Terragate this means maximum acceleration from the outset, with no over-driving or slipping and no delicate feedback encoder loop.

The integrated Hitachi 32-bit SuperH RISC processor delivers the response needed for high-end applications.

To compensate for possible temperature fluctuations within the motor, which might adversely affect smooth control of the motor, an online/offline motor-autotuning function is included.

An internal control process helps to reduce any rotational fluctuation at low speed, which for enhances gate stability and precision stopping during regular operation.