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Automation increases roof truss productivity

Automation increases roof truss productivity
When you are a manufacturer in the competitive roof truss market, how do you gain a competitive edge?  The answer for Shropshire based Engineered Timber Solutions Ltd was found in drive and automation technology supplied by Lenze through their Engineering Partner Tim Oxtoby.  Lenze inverters combined with a new control system reduced machine set-up times from what was 30 to 40 minutes down to less than 10.

Engineered Timber Solutions (ETS) are a successful company involved in the design, manufacture and supply of timber roof trusses for the domestic and specialist markets.  Here the trusses vary widely in profile and require individual design to suit structural loadings plus meeting more modern requirements such as  the mounting of solar panels.  Batch quantities at this end of the market tend to be low, hence set-up times are important.

ETS use a 9 year old custom-made machine to manufacture the trusses.  Similar to a gantry crane, it positions a head with two 17 tonne hydraulic presses using two axes of motion over a working bed.  Also on the head is a laser projector that marks out the position required for the plates that connect the timber beams, known as nail plates.  To set up the machine, the operators set the lower nail plates onto tables to the positions designated by the laser.  The gantry head moves from one nail plate position to the next until all the truss joints are laid out.  The timber beams are then put into position on the tables and an upper nail plate is added. The head is then driven back over each table position where the hydraulic rams create the joints by pressing the nail plates into the timber beams.

The dimensional accuracy that is required and achieved by ETS on a finished timber roof truss is quite remarkable. Joints are made with repeatability better than 1mm on the joint position with trusses that can be 10m long.  This accuracy is achieved with Lenze inverter drives of the series 8400 Topline which give servo levels of accuracy with encoder or resolver feedback.  Two gear-locked inverters drive the beam from either side along rails. The third drive moves the head with the laser projector and hydraulic rams across the beam.  Working over a floor area that exceeds 100m_ the drives are able to achieve positional accuracy for the head at about 0.5mm.

Lenze Engineering Partner Tim Oxtoby handled the complete project from concept, design, software and commissioning.  His company supplied a new control panel for the drives with a motion controller and made the installation. Tim has been working as a system integrator since 1996 with particular drive and automation experience with plastic processing, packaging and pick-and-place machinery. He was pleased with the Lenze inverters commenting ''The Lenze 8400 Topline inverters met the required accuracy and the ''Engineer'' parameterisation software was particularly easy to use allowing fast set-up without spending time on the manual''.

The ETS machine with laser projector and head mounted on the travelling beam is a unique approach to manufacturing roof trusses.  Standard practice elsewhere is to roof mount the projector in a fixed position but this makes it difficult to achieve high accuracy as thermal and wind effects on the building cause small movements.  The ETS machine has a consistent 1m long vertical path for the laser, and this short projection length also ensures a brighter image which is easier for the operators.

Engineered Timber Solutions specialise in designing roof trusses with the required structural calculations in a way that maximises the available space for their customers.  The design software connects directly to the laser head and projects a 700mm square image of the truss joints.  Managing Director Phil Sankey comments ''Despite the recession in the building industry we remain busy and need the ability to increase output.  I am very pleased with the savings in set-up times and the lower unit costs''.

With this small batch production of roof trusses where quantities, for example for loft conversion, can be in single figures, set-up times are critical.  The new drive and automation system supplied by Tim Oxtoby with Lenze 8400 Topline inverter drives has taken up to half an hour out of the set-up and also improves the accuracy of the trusses.  As the machine requires six operators with additional people cutting the timber beams, smooth and efficient production has a major effect on profitability.
 

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