Integrated Motion Control
Applications
Rotary Knife with Ultra5000 Intelligent Positioning Drive
Rotary knife systems are widely used in the converting and printing industries. A rotary knife must speed up or slow down when it is not in contact with the material to provide specific cut lengths. Rotary knife mechanisms consist of a cylinder with a knife blade (or blades) fastened along the longitudinal axis. As the cylinder rotates, it cuts the material passing under it. If the tangential speed of the knife matches the speed of the web material, the length of material cut will be equal to the circumference of the knife. If the tangential speed of the rotary knife is faster than the web speed, shorter cut lengths will be produced. If the tangential speed of the knife is slower than the web speed, longer cut lengths will result.
To obtain the highest quality cuts possible and to avoid damaging the web material, the tangential knife velocity must match the linear speed of the web during the portion of the rotation that the knife is in contact with the web material. Thus, in order to obtain cut lengths that are shorter than the circumference of the rotary knife, the knife must speed up when it is not contacting the web, and then slow down to match the web speed when it is in contact with the web. The converse is true when longer cut lengths are required. The knife rotation speed must decrease when it is not in contact with the web. To manipulate the length of material cut, the controller is commanded to change the knife speed to different values during the portion of the cycle when the knife is not in contact with the material.
Rockwell Automation Solution
An Ultra5000 Intelligent Positioning Drive with cam capability is used to control a rotary cutoff knife. The cam capability provides smooth speed transitions and exact speed synchronization when the knife contacts the material.