Introduction
For healthcare packaging, recent technology advancements have made in-motion weighing operations more precise and profitable.
Checkweighers used in healthcare packaging operations prevent the underfilling and overfilling of product, resulting in brand protection and cost reduction due to less product giveaway. Reducing product giveaway is simplified by utilizing the checkweigher’s filler feedback capability; the cost reductions achieved with a checkweigher implementation usually result in machine return on investment (ROI) times of well under a year.
Like many crucial machinery items, technology has evolved in recent years. The latest and greatest checkweighers incorporate weigh cells featuring Electro-Magnetic Force Restoration, or EMFR. Let’s discuss what this entails, and how it compares to conventional weighing methods.
What is EMFR Technology and How Does it Work?
EMFR systems can be compared to a simple beam balance – though the intricacies are anything but. Incoming weight on the load plate causes the lever arm (1) in Figure 1 to leave its nominal resting position. The position detector (2) recognizes this slight position change and forces the coil (4) on the other side of the lever arm to move out of the magnet’s field (3).
When this occurs, a photoelectrical beam recognizes any minute deviations in lever arm position and immediately sends its findings through a measurement resistor, transforming this data into a digital signal via an analog-to-digital (A/D) converter. The resulting digital weight value is determined by an advanced digital signal processor at exceptionally fast speeds with an internal sampling rate of 1mS, or 1,000 weight values per second. The weigh cell’s digital signal processor output is sent to the interface connection of the checkweigher or other third-party OEM device or machine.
With their lightning-quick sampling rates, EMFR-based weigh cells enable extremely accurate weighing results that provide space and cost savings when integrated into existing systems. They also possess high throughput rates, as high-speed checkweighers can capture product weights at rates up to 600 units per minute. Small and mid-range checkweighers offer fantastic price-top performance ratios, and all EMFR scales deliver increased plant efficiency thanks to precise and reliable weighing results. It’s no wonder EMFR-based solutions are used by prominent healthcare companies to help ensure mission-critical quality control.
The Benefits of EMFR Technology
Dead Load Compensation and Resolution
Compared to conventional strain gauge scales, EMFR weighing offers a number of benefits. When compensating for a dead load, traditional strain gauge-based checkweighers require a stiffer load cell to process the weight. With strain gauge checkweighers, the resolution of the weighing range declines. Since many load cells like the one illustrated in Figure 2 rely on a relatively large amount of metal bending, they all exhibit a spring-like operational behavior, called “ringing.” These type of cells cannot tolerate fast weight changes because this ringing action needs to be compensated within the load cell. Dead load weight also needs to be compensated, and it is more cumbersome to accomplish in strain gauge-based load cells.
Since EMFR weigh cells do not rely on large degrees of metal deflection, ringing is not a major concern. EMFR scales also can balance dead load with far less cumbersome software commands, keeping the weighing range available and the resolution intact.
Settling Time
When measuring dynamic performance, EMFR checkweighers have a short settling time and active attenuation by the electronic controller, while preventing sensitivity and resolution from changing - eliminating the need for constant calibration checks. As seen in Figure 3, strain gauge checkweighers generally possess less effective dampening oscillatory systems and a higher resonance frequency while settling, while the stiff load cell reduces sensitivity and resolution, requiring consistent calibration and maintenance.
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By contrast, EMFR scales are faster, more efficient, more precise, and require less maintenance than conventional weigh cells. Since EMFR modules accurately acquire product information faster than a load cell, this enables more weight samples per unit of time. This is one of the major reasons EMFR based checkweighers provide more precise product weigh information at much faster throughput speeds.
Application Example
Some of the EMFR weigh cell-based checkweighers used in pharmaceutical, healthcare and medical device packaging are similar to those used in food packaging applications – but with niche-specific enhancements.
For example, the model HC-A-Pharma shown in Figure 4 is very similar to a food-grade HC-A checkweigher, but also offers the ability to easily integrate into serialization applications as mandated for many prescription products. The model HC-A-IS checkweigher uses an indexing wheel rather than a belt conveyor to bring products to the checkweigher, making the module well-suited to round, cylindrical product packages such as inhalers, glass bottles and amber vials. The EMFR weigh cell in this checkweigher design is located in the 12-o’clock position, underneath the indexing star wheel. Depending on the star wheel design, up to four EMFR weigh cells may be incorporated into the machine design, allowing up to four product weights to be checked simultaneously.
EMFR Weigh Cell Application Example – Multitrack Checkweigher
Multiple EMFR weigh cells are also incorporated into belted checkweigher designs such as the one illustrated in Figure 5. The compact size that is possible with an EMFR weigh cell design makes it the ideal technology choice for this type of checkweigher design.
In the custom checkweigher shown in Figure 5, notice the five belts (i.e. lanes). Each lane has an EMFR weigh cell under the individual weigh bed conveyors, and they operate somewhat independent of each other. However, should the operator prefer, if one package is over or underweight, all five packages in that batch can be rejected.
What is AVC and How Does it Work?
Introduction
Active Vibration Compensation, or AVC, is based on fast sampling (FS) EMFR technology, and is an electronic method of removing the key portion of the ambient noise spectrum from a product weight signal using internal software tools. These noise sources are commonly found in factory and warehouse environments, and include conveyor sorters and fork lift trucks.
Why is AVC important? In just about every distribution warehouse, all available space is used. This means that there are multi-level sorting conveyors placed on mezzanines, and oftentimes the dynamic industrial scale or catchweigher is mounted off the ground in one of these vertical mezzanine levels. Rather than build super rigid mounting platforms for the dynamic scale to reduce vibrations, an AVC-equipped scale can be mounted using less expensive options because the weigh cell will compensate for the vibrations electronically.
Similar mounting advantages come into play with checkweighers equipped with EMFR weigh cells with built-in AVC used in pharmaceutical packaging quality control. Combining EMFR Weigh Cell technology with AVC sensors enables accurate product weight measurements.
How AVC Works
As illustrated in Figure 7, two weigh cells are mounted inside one EMFR housing, one weigh cell measures vibrations including the load to be weighed (1), while the other measures vibrations only (2). Vibration-based interfering variables are calculated by comparing the two measurement curves in the signal processing section of the EMFR weigh cell (3), where the major vibration components of the load signal are removed. Due to the FS technology, we are able to deduct the disturbing signal from the load weight signal and come up with a “compensated weight value.” The resultant measurement signal is very close to a load signal that would be achieved without any influence through vibration (4). This final weight measurement signal shows a major reduction, if not complete removal of the negative effects caused by interfering vibrations present in the in-motion checkweigher installation environment. Unlike filtering technology common in strain gauge based weigh cells, the AVC approach used in Wipotec’s EMFR weigh cells is unaffected when the disturbing signal (i.e vibration component) occurs within the same frequency range as the information signal or load weight signal. AVC is a patented technology only available in Wipotec EMFR weigh cells.
The Benefits of AVC Technology for Pharma
Serialization and Completeness Checks
In pharmaceutical packaging applications, it is necessary for manufacturers to put tracking codes on each individual package. The code content and code type is governed by several international regulations. Modules such as this TQS-HC-A machine interfaces with upper-level host software to acquire the tracking codes and print them on the individual cartons. The serialization codes are used to track and trace the packaged product throughout the supply chain in order to prevent counterfeiting. The code data makes it possible to find specific product(s) and recall them if necessary. Oftentimes a final completeness check by weight is done after the serialization code is applied. The EMFR weigh cell used in the TQS-HC-A machine offers an available AVC option. This option proves most useful for machine installations in high-vibration environments.
Summary and Conclusions
Electro-Magnetic Force Restoration (EMFR) is a technology proven effective in some of the toughest in-motion weighing applications around the globe.
EMFR eliminates the reliance on bending metal as a primary means of gathering weight data. The optical and electronic methodology approach employed in EMFR weigh cells result in faster settling times, and allow for the capture of more weigh samples as products move over the weigh cell. These checkweighers deliver more accurate, repeatable weighing results at faster production line speeds compared to conventional strain gauge-based checkweighers.
Active Vibration Compensation (AVC) is incorporated into some EMFR weigh cells to electronically reduce or eliminate the affect that low-frequency vibrations may have on the weighing results obtained by checkweighers. These environmental vibrations are common in production facilities and warehouse distribution centers. The source of the vibrations are typically conveyors, mechanical sorters, forklift trucks, and other machinery.
A typical AVC implementation involves two weigh cells located inside the EMFR housing, where one of the cells senses ambient vibrations of a certain frequency range. Signal conditioning is employed to reduce or eliminate these vibration signals from the weighing signal, resulting in accurate product weights in envionments where that may not have been possible with conventional strain gauge or load cell technology.
Author Biography
Jim Renehan is Senior Marketing Manager for WIPOTEC-OCS, a leading manufacturer and supplier of precision in-motion weighing and X-Ray scanning equipment