Cognex camera InSight 1400 output conversion into 4-20mA

[PX200]

Hi guys,


As a topic title says.. If someone would be so kind to point me in a direction..

ATM I am mostly concerned about camera value output continuosity..

Which means - those vision cameras ( in this case some Cognex 1400 b&w model) outputs values only when triggered.

This particular application is to measure some height which is afterword processed at industrial PC as in/OUT of tolerance.

Since is rather complex to change PC SW also - what I would like to do is to swap laser distance sensor (4-20mA output) with a Computer Vision Camera.


I think that camera can be placed in continous mode so the measurement will be constantly "feeded" to the output - but question is - how to easiest convert it into a 4-20mA for PLC


I know that question I ask is very "in general" but if someone could point me towards somewhere - it would be of great help also..



Kind regards.

 

[dmargineau]

Welcome to the Forum!

This should be a pretty simple Digital to Analog conversion.

Empirically determine the Min. and Max. values returned by the vision system when Min. and Max. height parts are being measured.

Once the Digital 'limits' are established 'transpose' (Scale) them to any Analog Output circuitry setup as Min. Height Value = 4mA and Max. Height Value = 20mA.

No matter the chosen automation platform, Analog Outputs follow ordinary linear (first degree) functions with user defined Min. and Max. values (axii intercepts); the function 'slope' is determined by the chosen Analog Output type- 4-20mA, 0-10VDC, -10 +10 VDC, etc.

 

[PX200]

Kind thanks for your welcome & answer.


I had issues about nomenclature of a such device (which soppouse to perform convesion to mA) thus isssue to search for it on the net.

I think I am going with this one "serial to analog" converter

https://www.laurels.com/transmitter-serial2analog.php

But if you have any suggestions - you're welcome..

By looking in the user manual it looks that it'll fit to my neeeds.

Kind regards

 

[dmargineau]

Your choice of Analog Output will generate the 4-20 mA signal proportional to the Serial RS232 or RS485 module input data.

Unfortunately, the chosen vision system (Cognex InSight 1400) does not provide any Serial output signal provisions; there are available Cognex interface modules ENet to IO and Serial Output(CIO-MICRO, CIO-MICRO-CC), however, this addresses only the electrical circuitry of your intended functionality.

The most important matter, the data transmission protocol, is still missing; either the vision system or the Analog Output module do not have protocol implementation and 'data handling' features.. You could run several different protocols on a RS232 or RS485 electrical circuitry of which the chosen Analog Output module supports Modbus RTU, Modbus ASCII and Laurel ASCII, however, you will still need a 'protocol processor'.

Within the Automation World, the dedicated data processors are the PLCs (CPUs); you will need one in order to process the vision generated data and 'transform' in into an analog signal.

 

[Mispeld]

It's not clear the motivation to change technologies (laser displacement to machine vision), though the implication is that vision technology will be only used for a height measurement. If true, my advice is to reconsider the decision to use a vision camera in this application.

While it is possible to use a camera such as the Micro 1400 to measure the size of objects in an acquired image, it will likely have much more complexity and cost than a laser displacement device. For example, lighting, calibration, optical distortion, plus the camera programming to acquire and process the image.

There could be some aspects of the application not clear in the original post (e.g., microscopic inspection) where the complexity of machine vision may be appropriate. With just about everything I can imagine, this sounds like the "worst of both worlds:" using more complex technology than necessary for the task, and then trying to force the machine vision interface to an analog signal.

Please take this as constructive advice. As noted, I do not know the details nor other motivations to change measurement technologies.

 

[PX200]

@Mispeld

Kind thanks for your reply & suggestion.

Reason is because I need to measure insertion depth in glass object (carpule)

Laser distance sensor is not suitable for that.

Carpule glass heavily dissipate laserspot light and measurements are very intermittent.

For various Carpule displacement - stopper( aka plunger) is inserted on various depths (within tolerances - off course)

Currently my colleague is testing an confocal sensor from micro epsilon - but we have difficulties for placement of it. It's too big.

What we masure is this:

@dmargineau


Yes - you're on spot for what you're been saying.


I need CIO Module to get RS232 out of 1400 camera. Sorry if I misslead you which Camera I can obtain - I am not familliar with Cognex products and their naming and product groups are human unreadable.

Cognex camera labeled ISM1403-01 is actually a Series 8000 camera

http://www.cognex.com/products/machine-vision/in-sight-micro-vision-systems/models/

and Cognex camera labeled ISM1400-01 is a Micro series camera.

Nevermind. I am new at this



So - I have IS-5600 also on my disposition (can be "borrowed" from currently inoperational machine) - I thik that serial output can be enabled on that one.


Plan is to, make backup of .job(s) - take it off and try to enable Serial in continuous mode with some fully simple .job to see if I can get the useful data on RS232 on a laptop hyperterminal.

 

[Mispeld]

Yes, the details make the difference, and machine vision is a completely reasonable approach.

From an interface standpoint I understand the desire for a "drop in" replacement for the existing device with a 4 - 20 ma output. But...these Cognex cameras are very well suited for a networked interface, and it might be overall easier if your Industrial PC software vendor/developer can add OPC support to the application in order to leverage the Cognex OPC server to get information out of the camera.

If the answer is "no" to touching the PC software, I would go so far as to recommend adding a CompactLogix PLC to interface with Cognex camera by Ethernet/IP, and then provide the analog output. It seems like a "sledgehammer" approach, but you will have a lot of flexibility, especially if you already have Rockwell infrastructure (i.e.., RS-Logix 5000 license). There are likely alternative PLCs to accomplish this; my experience base is only A-B.

Lighting and triggering could be challenging since it is implied the bottles are moving while being inspected. You may need some synchronization and strobing to get good images. With a good image, you may be able to use content for self-calibration, such as measuring a known bottle height.

 

[PX200]

@Mispeld - measured object will be (actually is) still at inspection point.

..so no strobe triggering or other complexity addon. Just need to get constant output from camera & easiest way to convert it to 4-20mA afterwards.

as for "no" to touching the PC software - you're right on that one.

It's not due to reprogramming or eventual technical issues, it's because machine SW is qualified by demanding SW qualification process and it would be required lot of paperwork to re-qualify it again.



Kind regards