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Cutting of rolled materials

Two-axis coordinate machine

An order has been received for the modernization of a disc roll-cutting machine (bobbin cutter).
This machine was operated by Siemens S7-300, the software was developed by an equipment manufacturer in Germany back in 2008. Several components of the control system failed, and the manufacturer refused to provide the source code. Since it was not possible to restore the system, the customer decided to replace the equipment with OWEN, EKF and PURELOGIC. The customer had accumulated experience working with this equipment, all the algorithms of operation of this machine were clear.
Roll cutting
Externally, the machine looks like this

The machine is designed for cutting large rolls into tapes of a given thickness (for example, double-sided tape). The machine has a rotating shaft on which the cut roll is fixed, a rotating disc knife with a drive mounted on the carriage. The carriage, in turn, moves along the X and Y axes. Along the X-axis, it shifts along the roll of the material being cut, along the Y-axis - perpendicular to it, that is, the cutting width is selected along the X-axis, and the knife approaches the material along the Y-axis-Cutting.
The shaft on which the roll is fixed has a polyurethane coating up to 4 mm thick, which, when the shaft is touched with a knife, ensures the safety of the knife. The required accuracy of touching the shaft with the knife was set to 0.5 mm.
A change in the speeds of movement of the knife along the Y-axis has been implemented, that is, when approaching the material, the speed is high, since it is essentially idling, when tapping and moving in the material, the speed decreases, when cutting through the spool, the speed becomes minimal, since it is cardboard and creates high cutting resistance, adjustable pause at the end of the cutting cycle and high the speed of returning the knife to its original position. Timely supply of coolant to the knife and sharpening of the knife during the cutting process is also implemented.

EKF Panel
EKF Panel

The project used two Leadshine servos, two frequency converters, an EKF visualization panel, a OWEN PLK110-60 controller, which provided control of fast outputs and reading of two encoders, control is organized by means of Step/Dir signals with position control by encoders. Leadshine drivers have the ability to select the resolution of the encoders, which was selected 0.08mm per 1 encoder pulse.
It is also possible to select the number of Step pulses per 1 turn of the drive in the servodrivers settings. The frequency of 100kHz given out by the maximum plk110 is quite enough to realize the movement of servos in the entire speed range.
The servos are connected via a flat-toothed belt drive to a ball-screw pair, which in turn moves the carriage with a knife. For 1 turn of the drive, we have a linear carriage movement of 3.33mm. Limit switches are installed at the beginning and end of the axis to limit movement along the axes. There are also protective limit switches located immediately behind the main ones, they are required in case of failure of the main ones and carriage slip through them. Also, servos and frequency drives of the shaft and knife report their malfunctions to the controller, which in this case turns off all systems and informs the operator about the corresponding malfunction.

Servo belt drive   
Flat-toothed belt drive to the servomotor

The Leadshine servo driver. This driver is good because it has an incremental encoder output that greatly improves accuracy

Purelogic Servo

Measurement accuracy
Acceptable accuracy results have been achieved. The system repeats the result multiple times without accumulating an error

Cabinet after modernization

The servos were selected by analogy with those that stood earlier (speed / torque). In fact, we copied the behavior of native electronics, repeating all the basic schemes that were implemented earlier by the Germans, we slightly modified those places that were a bit shoeless in the native version. The customer had experience working with this machine

The general algorithm of the program: at the beginning of working with the machine, the operator selects the manual mode from the panel and translates the axes to zero points. The zero points of the axes are connected to the limit switches that are included in the software. By the method of visual input of the knife to the material, the operator stops the Y-axis in the right place and stores the data values according to which the material will be cut in automatic mode, sets the width of the strips (shift along the X-axis). The automatic mode performs cyclic operations in accordance with the setting of the values of the specified points of movement and, accordingly, the set speeds of movement from point to point.
The distance calculation was selected from the ratio of the number of pulses received from the incremental driver encoders per millimeter. 120 pulses per millimeter came out.
The maximum clamping force of the knife to the tube is adjusted from the driver program and selected empirically
The program contains the necessary safety sensors, such as an emergency stop button, end position sensors, and a protective shield limit switch. Relay protections have been created that do not allow the operator to disable the machine.
Is it possible to accomplish this task, for example, using cheaper stepper motors?
Servos work similarly to stepper motors, adjusted for the presence of motion control by incremental encoders and an increase in torque with increasing rotation speed. The servo settings solved the problems with energy, when the drive skipped the desired point, there were reciprocating movements, the servo tried to catch a given position moving back and forth. Solved the problem by reducing the speed when approaching a given point

Video clip

#Two-coordinate setup, #PURELOGIC, #OWEN, #PLK110, #EKF, #PROSSCREEN

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