Sawn to length with ‘spot-on’ precision

In order to service customer demand, the company recently commissioned a new saw table to increase its production capacity. A machine frame and 6.4m long belt-driven linear slide were duly constructed using the Item MB modular system, with Lenze System Partner, Cornfield Engineering Solutions, providing all the necessary motion controls required to cut the aluminium profiles to specified lengths.

Cornfield's drive system, with HMI, frequency inverter and geared motor, positions a carriage holding the end stop so that a circular saw can cut the aluminium profiles to length with a high degree of precision. Indeed, thanks to the latest drive technology deployed on this motion control application, system performance often surpasses MBS’ specified cut-to-length accuracy of ±0.1mm.

Profiles to be cut are manually fed up to an end stop which is set by the position of the carriage. Consistent positioning accuracy was required over the full 6m travel of the end stop. An operator interface allows easy entry of the required profile length, together with a display of the actual position.

Cornfield’s Lenze equipment based system is noteworthy, in that there is no controlling PLC. Positioning control is also achieved by the drive’s integral systems, and the motor is unusually compact for an application of this kind.

Positioning is achieved via a program resident in the Lenze 8400 TopLine inverter. This top-of-range model was chosen as it has offers standard point-to-point positioning with controllable ramps. In addition, it accepts inputs from both the motor resolver and from an HTL linear incremental encoder – a key factor in the high level of accuracy obtainable with this system.

CANopen communication capability is a standard feature of the drive, and this is used to integrate the HMI - a Lenze EL106 unit with a 6.4in colour touchscreen – into the overall control system. Moreover, the generous analogue and digital I/O capacity provided by the inverter means that it is able to control all of the machine functions, resulting in simplicity and low cost.

A Lenze bevel geared motor type GKR03 provides the mechanical transmission.  The gearbox offers low backlash and a particularly low wear rate making it particularly suitable for this application, which involves both reversing and rapid positioning duties.

The 0.75kW motor in this configuration was chosen from Lenze’s inverter-optimised MF range and is designed to run at a nominal speed of 120Hz. The main advantage of this selection is one of physical size – the higher speed allows the 0.75kW power to come from a 63 frame size motor instead of a 4-pole motor with an 80 frame. The reduction of two frame sizes also reduces the weight, inertia and cost.

The 120Hz nominal speed, which is equivalent to about 3,500rpm, gives a wider useable speed range of 17:1 without a blower. As it is not rated at mains frequency, the motor falls outside the scope of the ErP regulations for energy efficiency; however, the higher speed does increase running efficiency so that IE2 levels are surpassed.

Cornfield worked with MBS to specify the system and wrote the drive program using Lenze’s L-force Engineer software, and the visualisation using Lenze VisiWinNet software. Following installation and on-site commissioning, Cornfield director Chris Timbey expressed delight at the system performance.

“The use of the latest Lenze drives and automation equipment has made a system that is both simple and high performing,” he says. “MBS asked for a length accuracy of ±0.1mm and we have actually achieved better than ±0.05mm - and often spot-on!”