Quality control using weight detection

The weighing of small items at high throughput speeds calls for exceptional precision of all components involved. To ensure reliable processing, even the slightest deviation has to be detected with supreme accuracy. This demands a high degree of synchronized ­precision when feeding and removing the objects to be measured. The requirements of the industrial scale itself are even more ­stringent. Neither the conveyor belt nor the drive may cause any disturbing vibrations. Precisely controlled and smooth-running sine wave commutated DC-Servomotors are the perfect solution for such demanding tasks.

Industrial manufacturers often produce small, lightweight products in bulk. Fill quantities or completeness can then be conveniently measured using an ­industrial scale. In the majority of cases, they are mass-produced goods where both pre­cision and high-throughput monitoring are critical for quality ­control. Weighing specialist Mettler-Toledo Garvens GmbH has developed its XS1 checkweigher ­specifically for this field of application. In cooperation with drive specialist ­FAULHABER, the weighcell was equipped with a smooth-running ­conveyor belt – including a controllable drive – that operates without adversely affecting the weighing process. Fast, jitter-free ­transport and precise weight detection are thus combined to provide high output ­performance.

Fast weighing

Law requires that many of the items ­produced day in, day out meet certain weight specifications. For example, the weight of various packaged goods in the food industry must be checked ­thoroughly after production. The dynamic XS1 checkweigher allows classification in up to seven weight classes. With a permissible maximum weight of 200 g and a ­resolution (accuracy) from +/-0.015 g, the smallest of deviations can be determined quickly and efficiently. An operator-friendly touch screen display listing requisite weighing data ensures easy setup and operation. Delivering proven functionality, the ­system includes automatic or manual zeroing and is designed for flexible integration in ­production lines. Additional features such as trend control for automatic filling ­process control, statistics, analysis programs, etc. provide the basis for process-specific adaptation. In order to feed the checkweigher with the required test ­pieces as quickly and reliably as possible, the overall system includes conveyor belts on both the infeed and outlet side of the actual weighcell transport belts. Their speed is synchronised with that of the weighcell transport belt. This ensures that the transport process itself has no disturbing impact whatsoever on the weighcell in a horizontal direction. Transport within the cell is ­subject to even stricter ­standards. Both the belt and the drive motor must run as evenly as possible in order to ensure the precision required for the actual weighing process. The system is equipped with an easily controllable, smooth-­running dynamic DC-Drive. The special sine wave commutation reduces the motor torque ripple to a minimum and further increases the overall ­running smoothness.

DC-Servomotor

The sine-commutated DC-Servomotor has an output of up to 90 W under constant operation, bringing up to 160 mNm torque to the drive shaft. Pre-loaded ball bearings eliminate vibrations from the rotor, and the special design of the ­magnetic circuit provides the optimal magnetic flux path in the motor. In ­conjunction with the sine commutation, this results in very low torque ripple and exceptionally smooth-running. The motor is available in two versions: with serial or CAN-bus ­controllers. The integrated Motion Controller handles the following drive tasks if required, without resorting to external computer power: speed control, speed profiles, positioning operation, stepper motor operation and electronic gearing. Motor configuration parameters can be altered and saved on the OnBoard ­memory of the drive. What is more, the Motion Controller is responsible for ­monitoring the operating temperature and overvoltage. It also takes the appropriate "protective measures" in case of undervoltage in the power supply. Thanks to its integrated technology and bus ­connection, the drive is suitable for a wide range of challenging applications – without the need for bulky cable harnesses. The sine-commutated DC drive with integrated intelligence is particularly ­suited for areas of application in which dynamic performance and high resolution speed control are paramount. ­Whether in decentralised automation technology ­systems or handling and tool machines, equipping the systems with their own intelligence and a bus ­connection for external communication is the perfect solution for tailor-made ­applications.

The XS1 (Mettler-Toledo Garvens GmbH) is a state-of-the-art checkweigher for small, high-throughput products