Maxon’s MCD EPOS integrated power drive was used by a wine and liquor bottling operation to control the cutting of shrink-wrapped film over the bottleneck and cork or cap.
In wine and liquor bottling machines, a film is shrunk over the bottleneck and the cork or cap, a so-called bottle cap. Two different modes of operation are used to cut the film to the desired length. The first method advances the reel-fed band by a fixed distance after a starting signal. Then, a digital signal activates a pair of scissors cutting the band. The second method uses a marking on the band which is detected by an optical reader and initiates a relative position move. Again, the scissors are activated. The selection of the mode of operation is set at the beginning by a digital signal.
The filling machines have an expected life of several decades if properly serviced and maintained. During the life cycle, faulty modules and sub-functionalities may be replaced, improved and modernized. This is made easier by a basic modular conception of the machine. Traditionally, a stepper drive controlled by the main PLC was used to cut the shrink-film. A redesign of this function uses a programmable Maxon compact drive, the MCD EPOS P. The underlying goal is to put the modularization one step further by transferring intelligence to the local drive.
Another important aspect is to reduce the outer dimensions of the drive and at the same time achieve a higher force. The requirements are at least three working cycles per second. These conditions are optimally fulfilled using a brushless DC motor as found in the MCD EPOS, combined with a Maxon ceramic gearhead GP 32 C (reduction ratio 18:1), to improve life expectancy. The MCD is smaller than the existing controller and fits perfectly below the feeding roll with the gearhead. A toothed belt transmits the torque from the gearhead to the roll with an additional reduction of 2:1.
The local PLC functionality is built into the programmable MCD EPOS P 60W and controls the complete cutting operation. The drive receives a digital signal from the main PLC defining the mode of operation. Upon the starting signal, the complete process is controlled locally. This means the signals of the optical sensor and the state of the scissors are read, the position moves with the motor executed and the scissors activated. The digital outputs are used as well to provide error signals and to activate the inputs. When replacing an existing design with a redesigned module, it is important that the existing interfaces for the rest of the machine may continue to be used.
Programmable Drive Unit
The small, and light weight compact drive MCD EPOS P with 60W power rating perfectly fits the requirements of the application. Motor, encoder and motion controller are all integrated into an aluminum housing, allowing protection up to IP 54. All internal connectors are vibration-proof and suitable for a harsh industrial environment. The brushless DC servomotor achieves high power density and long life expectancy. Due to the high starting torque, an excellent dynamic behavior is obtained. The slotless winding allows smooth operation without cogging even at the lowest speed. This is further supported by the sinusoidal electronic commutation scheme of the controller. The digital incremental encoder with 1000 counts per turn results in 4000 positions of one motor revolution or a nominal resolution of 0.09°. Combinations with gearheads are foreseen to increase the torque.
The motion controller used is a member of the Maxon EPOS family, a modular positioning system with the CANopen filed bus interface. It can be used as a speed, torque and position controller. The motion controller is integrated in the slim and compact housing, without increasing the outer dimensions of the drive with any protruding parts. The sophisticated heat management of the power stage is made with a printed circuit board specially mounted on an aluminum support. This allows the electronics to be kept small and yet get the full rated power from the motor. The power stage is optimally adapted to the power requirements of the motor.
Due to the opto-coupled configurable inputs and outputs, all kind of signals from the drive periphery can directly be connected, i.e. end switches or reference switches.
The MCD EPOS P 60W includes a PLC functionality with a CANopen master. Decentralized drives can be realized in a most simple manner. At the touch of a button, an autonomous movement may be executed, and at the same time local digital outputs and inputs can be set, read and used to control the program sequence. In addition, there is the possibility to create networks of multi-axis systems by means of the CANopen communication.
The programming of the integrated PLC complies with the international standard IEC 61131-3, as opposed to many other small drives which are programmed by some proprietary language. Free software tools and programming libraries are included.
The advantages of the new solution for cutting the shrink film using the EPOS P 60 W include compact size, the built-in intelligence, and the strict application of industrial standards which simplify the integration and the flexible replacement of existing modules. This application example illustrates a typical and growing trend towards miniaturization. This trend can be found in drive technology as well where it is tackled by two strategies. In appliances made in larger quantities, the drive components are designed to fit into the overall system. Mechanical and electronic interfaces are adjusted precisely to match the application.
For example, the lead screw and the gearmotor may be one entity, or the motion control may be integrated into the electronic controller of the complete appliance. In the industrial field, modularization is very important, which means that compact drives are achieved by integrating motor, sensor and motion controller into one housing.
This article was written by Urs Kafader of Technical training, maxon motor in Switzerland. For more information, contact Maxon Precision Motor at 508-677-0520, or visit http://info.hotims.com/15140-326.