AC Drives Improve Safety of Woodworking Machines

The Challenge

Tighter requirements for the emergency stop feature on woodworking machines, which stops the heavy, high-speed vertical milling heads moving when an access door is opened, were brought in, meaning that DC brakes were no longer up to the task. Krüsi turned to Fichter and Zimmerli for a solution.

The Solution

The woodworking machines are manually fed with wood sections, a clamp is applied and the machine goes through a programmed sequence under PLC control, drilling and milling out interlock corner joints for the log cabins / block houses, the average time per cut being just 15 seconds. Either four or five Commander AC drives were fitted to each machine, providing control of the vertical movement and rotation of the drill and milling heads (7.5 kW drives) and, on some of the machines the control of the cross cutting saw too (a 5.5 kW drive). The access doors were fitted with interlocks, which return an ‘open’ signal to the PLC when opened, initiating an emergency shutdown during operation, stopping all rotating movements within the space of two seconds, even if the milling head is rotating at full speed.

The Benefits

Fichter and Zimmerli recommended Commander SK drives from Control Techniques because they offered the best combination of price and quality, dynamic performance, and because the drives’ compact size meant that the overall panel size was smaller, saving panel-building costs.