Precise carriage positioning using frequency inverter

Machine Building Systems Ltd needed a new machine to cut to length aluminium profiles for its Item product range. The machine frame and 6.4m long belt-driven linear slide was constructed using the Item MB modular system, and Lenze System Partner Cornfield Engineering Solutions Ltd provided the motion and control for positioning the end stop. Cornfield supplied a complete drive system with HMI, frequency inverter and geared motor. The system positions a carriage holding the end stop so that a circular saw can cut the aluminium profiles to an exact length. By using the latest in drive technology, performance has surpassed the requested accuracy of +/-0.1mm on cut length.

Machine Building Systems is well known for the Item MB aluminium profile system it supplies for use in machine frames, guarding and work stations. The company offers strong technical support backed by substantial UK stocks. Cornfield Engineering Solutions is a Lenze System Partner based in Stoke-on-Trent. Led by Director Chris Timbey, the company has 10 years of experience with drives and automation, particularly in the ceramics, food and packaging industries. On offer is a complete service from assessment and design through to software writing, installation and commissioning.

Increasing production capacity

The new saw table was required by MBS to increase production capacity. Profiles to be cut are manually fed up to an end stop that 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 system using Lenze equipment is notable as there is no controlling PLC; positioning is achieved using the drive alone. Furthermore, the motor is unusually compact. The positioning functionality is achieved with a program built into the frequency inverter type 8400 TopLine. This top-of-the-range model was chosen as it has as 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, resulting in the high level of accuracy achieved. CANopen is fitted as standard and this connects to the Lenze EL106 HMI with a 6.4 inch colour touchscreen. Generous analogue and digital I/O connections in the inverter mean that it is able to control the complete machine functionality, resulting in simplicity and low cost.

Efficient running

The electromechanics of the drive are a Lenze bevel geared motor type GKR03. The gearbox has low backlash and a very low wear rate, suiting it to reversing and positioning duties. The 0.75kW motor chosen was from the Lenze inverter-optimised MF range 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 motor instead of a four-pole motor with an 80 frame. The reduction of two frame sizes also reduces the weight, inertia and cost. The 120Hz nominal speed, equivalent to about 3500rpm, gives a wider usable 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 with Lenze L-force Engineer software, also the visualisation using Lenze VisiWinNet software. After he had done the installation and commissioning on site, Chris Timbey was delighted with the system performance. He says: "The use of the latest Lenze drives and automation equipment has made a system that is simple with high performance. MBS asked for a length accuracy of +/-0.1mm and we have actually achieved better than +/-0.05mm, and often spot on."

Follow the links for more information about Lenze Inverter Drives 8400 TopLine, EL 100 series HMIs, MF series inverter-optimised motors, gearboxes and softwre tools.