Vibratory Feeding Technology Gets Sophisticated

In this article, Urs Helfenstein, R&D mechanical engineer at Coperion K-Tron, explains what makes the K3 vibratory feeders different from other feeding technologies.

Q. What factors affect the selection?

A. With vibratory devices, there are very different technologies available. For example, there are electric drives, which create a lot of noise. Then there are pneumatic devices, but pressurized air is an expensive power source. There are rotating masses to create vibration or oscillation, but in this case, you have moving parts, which means maintenance issues.

We went down a new road and examined how masses are balanced. Shock absorbers are essential when it comes to vibratory technology because you need to separate the vibration of the device from the environment or the structure where it is fixed. Without it, everything would vibrate and make a lot of noise, it would be very inefficient, and the weight measurement is badly impaired.

Most vibratory drives use shock-absorbing elements that are springs or rubber. We found that if it is on springs or on the rubber element, the vibratory drive can move in all directions. This has disadvantages. The oscillation can be very unpredictable. For example, if you have one material you have a certain center of gravity, but with another material that has a different density, the center of gravity may change and it causes trouble because it starts to oscillate differently. This is why some people think vibratory technology is not as reliable or predictable.

Q. How does K3 technology address that?

A. We use pendulums. They move only in one direction, that being the direction where we want to absorb these vibrations. But all other degrees of freedom are restricted. We achieve shock absorption, but we restrict all the other effects at the same time.

Q. What are other advantages?

A. One big advantage of the K3 technology is improved accuracy because we eliminated the pitch movement. We have the same motion for every section of the vibratory tray and the same speed of material, which with the other technologies, you have different speeds on the tray and material height changes over the length of the tray. With our technology, the material moves straight so you have a constant height. This means the material flow is much more controllable and responds to change much faster.

We did tests with different materials and with different feed rates and achieved 35% better accuracy on average when we replaced conventional shock absorbers with pendulums.

You find another important advantage in weighing. If less vibration acts on the scale, we have fewer disruptions during weighing. And together with this adaptive digital filter technology that’s integrated into the scale and adapts on its own to conditions, we don’t see any effect of vibration on the accuracy results.

Our K3 vibratory feeders have just a few moving parts. They have very low maintenance requirements and they’re much easier to clean than screw feeders.

Q. Are there any underappreciated aspects?

A. One thing that is not very obvious is the balance. We have a top part where the tray is mounted and there is a counter motion. So, if one moves up the other moves down and vice versa. And the centers of gravity of these two masses are oscillating in counter directions. If they are in line with the motion, you can reduce the vibration to the environment and scale a lot.

Q. What mistakes are made when selecting vibratory feeders?

A. It’s not an all-purpose device. It is only for free-flowing material. We do not have an enforced material motion like in a screw feeder. In some facilities, there’s a temptation to use vibratory feeders for non-free-flowing materials because of the advantages they offer.

Q. Are there special design considerations?

A. One point to be considered is we don’t have agitators inside, so it is more sensitive to blocking.

To remedy this, we have a technology called ActiFlow™, which uses vibration to break bridges in the hopper. It’s a smart device that ensures vibration is always just enough. If the vibration is not strong enough, it won’t break the bridges. If it’s too strong, it will compact the material and then it bridges even more than before. The device monitors the mass flow and compares it to the setpoint. It automatically calculates how much vibration is needed to keep the material moving. Many people prefer this over a mechanical agitator since it’s mounted outside of the hopper.

Q. How does the K3 differ from other alternatives?

A. We’ve talked about the pendulum shock absorber technology. There is nothing like this on the market.

What we haven’t talked about is the feeder’s hygienic design. We have a device that needs to vibrate. Usually, to allow these vibrations, you have gaps, but for hygienic environments you try to avoid gaps. We designed a silicone boot, which covers the entire drive. There are no gaps. It is completely enclosed.

Another difference is the controller itself. It is a closed-loop control. We measure the motion 1,500 times per second, and by measuring the motion, we can adapt the excitation signal of the coil in real time. Others do not measure any vibration, they only increase the signal or lower it. We measure the motion and compare it to the excitation and then we see if we are in resonance, and we drive our vibratory in resonance frequency. Most of the devices on the market avoid resonance frequency. For example, if you are on a swing and you are moving in the right frequency, with a little motion you get a big oscillation. This means you’re in resonance. But if you move in a much faster frequency, you get almost no oscillation.

We measure the current 25,000 times per second and make adjustments to ensure a clean sine curve and very smooth motion. This reduces noise and vibration. Most devices on the market are pretty simple; they control the drive with an impulse or choppy signal. With our technology, we avoid inducing unwanted frequencies as these disrupt the material flow, they create noise, and they reduce efficiency.

To give you an example, we measured power consumption at a feed rate of 12,566 pounds (5,700 kilograms) an hour. We used only 20 watts of power to feed that amount. That’s a third of a light bulb. Because we drive it in resonance, we only need a little bit of energy to keep it moving. Compared to a screw feeder, we need about 40 times less energy for the K3 vibratory feeder.

Q. Anything you’d like to add?

A. We should talk about the weighing technology, which is a core competence of our company. We build our own scales and controls. Our scales are based on the vibrating string principle. If you apply more force to the scale, the vibrating wire is more loaded, and the resonance frequency increases.

By measuring this resonance frequency, we know how much weight is on the scale. We measure over 400 times per second with very high resolution. This high-speed measurement allows us to process the signal in a filter modified for the operating conditions, which achieves high accuracy.

Something else we haven’t discussed is pressure in the system. Pressure fluctuations exert force on the scale and can seriously impact the weighing accuracy of a feeding system. This leads to incorrect weight signals, causing erroneous mass flow and poor feeding accuracy. We’ve developed EPC electronic pressure compensation. We measure the pressure on the outlet and in the hopper. And if the pressure changes, we compensate this error on the scale electronically.

Coperion K-Tron holds numerous patents on mechanical components and control technologies for our feeding and weighing solutions. This experience allows us to tailor our products and services to the needs of various industries.

Published with permission from Chemical Processing. All rights reserved.