South Africa exports about 42% of its apple produce and of this 142 000 tons are packed by hand in order to display the produce as attractively as possible. The Sunny Side Packer was designed to improve on this unproductive, unpredictable and inconsistent approach to apple packing by automating, speeding up and improving the selective process of apple packing. The Sunny Side Packer is unique because it combines quick and efficient packing with the ability to display the best side of the apple. From a business perspective, besides packing boxes of produce quicker and more consistently (improving from 45 to 190 apples per minute) the system results in a higher perceived quality of the goods.
The proposed packing machine (with a packing speed of 190 apples per minute), is aimed at production managers and financial decision-makers in packing houses that serve the fruit and vegetable industry, and aims to improve the marketability of the produce. By boxing coloured apples with their best looking and best coloured side facing upwards more efficiently, there is a better perception of the produce, thereby improving its marketability.
The vision system
Festo’s Intelligent Compact Vision System (SBOC-Q/SBOI-Q) camera was designed to facilitate quality inspection, and enabled the Sunny Side Packer to detect and deliver consistent quality for each tray. Cameras were placed at a distance of 553 mm above the rotating apples, giving them a viewing angle big enough to see 300 mm of the singular chain. Two cameras covered the 600 mm length required for six apples.
The system
The Sunny Side Packer had a total of 10 axes. Movement along these axes resulted in the packing of 12 apples into two trays at a rate of 15 trays per minute.
The system was controlled by a PLC unit that used a PC for user input/output and image processing. The PLC had to be capable of communicating with six pneumatic controllers, one electrical linear actuator controller and three motor drivers.
The Festo CPX-CMAX controller – a very effective and compact mounting topology for the system’s drivers and control hardware – was used for actuation of the Festo DNCI cylinders. The CPX-CEC control block was perfect for the system requirements as it could control up to 31 axes.
Festo’s CPX-CEC-M1 was chosen specifically for its built in SoftMotion technology and was more than adequate for controlling the system’s electrical drives. Festo Handling and Positioning Profile (FHPP) technology enabled the control block to control the servo motor’s CMMP-AS-C5-3A controller, which in turn was used to actuate the Festo EGC. The SoftMotion technology also enabled the PLC to do interpolation in its control of the EGC. This ensured that the EGC was operated in the most efficient manner.
The CPX terminal came with an Ethernet adapter. This enabled the Festo CPX-CEC-M1 to communicate with the PC, which in turn communicated with the camera. The CAN-Bus enabled communication with the electrical drives in the system – the SEW-Eurodrive motors and drives. The CPX terminal had built-in connections for communication between the PLC and the CMAX controllers.
Movement and drive mechanisms
Apples were moved linearly and rotated through the system on a singulator chain. To ensure the efficient use of energy and motion, suitable driving mechanisms for both the chain and flat belt were selected. Acceleration and speed control were also fundamental to the application, and two SEW MoviGears were chosen to drive both the chain and the belt. The advantages of these close-coupled geared motor and drive systems above traditional drive systems were greater efficiency at any speed and torque; the gearbox was not overdesigned; a servo motor could be used; there was good speed control; and installation was easy because no external encoder, drive or gearbox were required. Cable losses were small because the drive unit and motor were so closely coupled, requiring shorter wires.
The SEW-Eurodrive MoviGear (MGFAS2-DSM-DBC-B) could produce the appropriate torque for the application. The MoviGear DBC-B was selected using SEW-Eurodrive’s drive configurator for its ability to have direct binary communication through the CAN-Bus.
The conveyor was moved by a geared SEW-Eurodrive AC servo motor. This motor was ideal for start-stop applications and could be used to move the belt in specific positional increments, at specified speeds. SEW- Eurodrive’s MoviTools was used to schedule the necessary movements. It communicated this to the MoviDrive, which controlled the motor.
The picker mechanism
The picker mechanism was designed to pick up the apples as quickly as possible and hold them securely for the duration of their travel. Suction grippers were favoured because they were hygienic and less likely to damage the apples. Festo’s Vacuum Selection software tool was used to select the gripper setup. The team noted that the fin grippers currently being developed by Festo would prove an ideal mechanism to use in this application.
The Festo vacuum generator VADMI-95-P was selected to generate the vacuum for the four suction grippers on each picker. With its integrated solenoid valve, this generator was easy to install and had an integrated vacuum switch and ejector pulse. The vacuum switch was required by the PLC to check whether an apple has been picked up or not. By applying a short pulse of positive pressure to the gripper just after the vacuum was switched off, the ejector pulse ensured that the apples were set down quickly and reliably. Festo EGC and DNCI equipment was selected to provide horizontal and vertical movement because of its ability to deliver precise, controllable movements and ensure reliable placement for successful pickup and placing operations at a reasonable cost.
For more information contact Renee Rose, SEW-Eurodrive, +27 (0)11 248 7000, [email protected], www.sew.co.za
| Tel: | +27 11 248 7000 |
| Fax: | +27 11 248 7289 |
| Email: | [email protected] |
| www: | www.sew-eurodrive.co.za |
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