empty box inside a carton

[Steve Bailey]

When I made the suggestion about striking the box and measuring the frequency of the sound it makes, I was thinking along the lines of the difference in sound when you strike a glass that is empty compared to the sound when the glass has some water in it. The pitch (frequency) of the sound increases with the height of the water in the glass. I think Peter was alluding to the same thing.

If the method works at all, it will work best with an elastic container, a quality not embodied in a cardboard carton. I have no idea if the difference in sound between a carton filled with 49 packages and one filled with 50 packages would be detectable by any available sensor.

 

[curlyandshemp]

thank you curleyandshemp for the website, i will put as plan B, but i still if availables sensors that i can put it inside the machine without redesign it.

Your application is exactly what a checkweigher is meant for, no sense trying to avoid the obvious. If this task was put to you by management, you can tell them you have exhausted all resources and come to the conclusion only a checkweigher can reliably sense one or more packages missing from a box.

Ian

 

[sinanissa]

When I made the suggestion about striking the box and measuring the frequency of the sound it makes, I was thinking along the lines of the difference in sound when you strike a glass that is empty compared to the sound when the glass has some water in it. The pitch (frequency) of the sound increases with the height of the water in the glass. I think Peter was alluding to the same thing.

If the method works at all, it will work best with an elastic container, a quality not embodied in a cardboard carton. I have no idea if the difference in sound between a carton filled with 49 packages and one filled with 50 packages would be detectable by any available sensor.

i do not means to check 49 of 50. i mean that to put two sensors above the carton, one for the left side, and the other for the right side, now the volume becomes 25 for each sensor. as the carton is moving, the sensor will check the first column: every column must contain 5 boxes, thus will take 5 readings. the machine speed is slow, and i think that time of detection is not important.

so every sensor will check if less than 5 boxes is found in each column, for 5 columns, for 2 sides, and total of 50 boxes.

do you know any sensor that will do such a thing?

 

[curlyandshemp]

do you know any sensor that will do such a thing?

If there is such a thing, it must be a weird and wonderful solution that not too many people know about. Look how many posts have occured without a definite solution other than an inline CHECKWEIGHER.

Ian

 

[sinanissa]

I am just searching.

inline CHECKWEIGHER

is a good solution, but all i am doing now is searching for other solution.

thanx for you a lot.

 

[curlyandshemp]

I am just searching.

is a good solution, but all i am doing now is searching for other solution.

thanx for you a lot.

What I was trying to get at, is that the checkweigher is the solution, it is guaranteed to work. I have seen many situations where management don't like the required solution and are always looking for a cheaper,simpler or easier way to do things. In the end, the right way was the only way to do it.

Ian

 

[Steve Bailey]

Curleyandshemp is absolutely right.

Of all the available methods, the best combination of cost and reliability will almost certainly be one based on weighing the carton. That may not be the answer you want to hear, but it is a fact. You will always be able to find people willing to offer an opinion on alternate solutions that might work for your application. Just remember, those opinions are free and worth every penny.

You will be able to find vendors of weight-based systems who will stand behind their products and guarantee their success because they can demonstrate successful implementations in more challenging applications than yours. As for the alternative methods, the best guarantee you may get is "Try it and see if it works".

 

[RDS]

I have used several versions of these with great success: http://www.filtec.com/case&.htm They make X-ray as well as gamma ray full or empty case detectors.

 

[Lancie1]

Cigarettes are not sold or packed by weight (but by count), so weight does vary, and how much variation in weight depends on how well the moisture content of the tobacco is controlled. Cigarettes have a low density, and in this case each box is only one-fiftieth (1/50) of the total, and the normal weight variation may be that large. Detection of missing boxes by using weight might be difficult.

Any method employed will not be so easy in this case.

An ultrasonic sensor has the required range, and sensitivity to detect a void (distance to last box), but it may be difficult to find a spot where the sensors can look only at sound reflections from INSIDE the carton. It would require one sensor be located directly in the center of the carton opening, and calibrated to pass only if all 50 boxes are reflecting sound.

Perhaps 50 ultrasonic sensors, one for each box space, 25 looking left and 25 looking right, mounted on a mobile swing arm that is moved into position, then takes the measurement, then moves out of the way again. Ultrasonic sensors are available with on/off outputs or 4-t0-20 miliamp analog outputs. Depending on space available, you could mount them on the swing arm in an array, 5 rows x 5 columns. I would use a PLC to multiplex (stagger) the readings, activating and reading a sensor on each side every 1/4 second, taking 6.25 seconds to read all 50. This would eliminate stray sound reflections between sensors.

This Keyence High Power Digital Ultrasonic, might work: http://www.keyence.com/topics/sensors/fw/release.php

With 50 sensors it will be good to perform a calibration test in between actual measurements. That can be done by a PLC, if a target can be located in the rest position.

 

[curlyandshemp]

Cigarettes are not sold or packed by weight (but by count), so weight does vary, and how much variation in weight depends on how well the moisture content of the tobacco is controlled. Cigarettes have a low density, and in this case each box is only one-fiftieth (1/50) of the total, and the normal weight variation may be that large. Detection of missing boxes by using weight might be difficult.

Any method employed will not be so easy in this case.

.

That may be true, but in any checkweigh application, it is always adviseable for QC to periodically check the weights of product being sampled by the checkweigher and adjust the limits of the checkweighers zones accordingly, or adjust the process feeding the checkweigher.

I see this all the time in the flour and milling industries. Soft wheat is like a sponge that absorbs moisture, and whose densisty changes based on how long is has been sitting in a holding hopper. Those two factors cause havoc in consistent automatic bag filling.

For s**ts and giggles, any smokers out there should take a carton of cigarettes and, if they have access to a pharmaceutical scale, weigh each individual pack of smokes. Based on the consistency of that test, that would determine the sensitivity of the checkweigher.

Ian

 

[Freak]

Alternative to ultrasonic is lazer which can obviously be used to detect a small area as opposed to an US that may be too wide, use it to measure distance.
Another option is radar, whereby you may be able to use just one sensor and program what it is lookign for.

Lazer - check IFM
Radar - check VEGA