Camera interface standards

It's my impression that the machine vision industry has pretty much standardized on one interface. It’s GigE for area or matrix cameras, leaving USB3 to the scientific/medical community and falling back on CameraLink for linescan applications. (Though I notice Dalsa now has a family of GigE linescan cameras.) However, I know other industries like other formats.

So, when I saw a post on the excellent Adimec blog asking, “Which digital video interface is best for global security systems?” I didn’t expect to learn much. But there were a couple of interesting snippets.

First, regarding GigE, “Processing required to pack and unpack video generates additional heat and uncertain latency…” Now that is news to me. Yes I have noticed a couple of my favorite GigE cameras seem to run very hot, but I hadn’t compared them with USB3 equivalents. Now I think I will.

Second, someone seems to have a bit of a downer on USB3:

“Cons

• Large connector and interface driver
• Maximum throughput unpredictable (chipset, PC motherboard and driver dependent)
• Sustainable speed is much lower than theoretical limit
• Unreliable operation with longer cables (>3 m)”

Interesting points. There’s been so much hype over USB3 that the downsides seem to have been forgotten. Good to see Adimex removing the rose-tinted specs.

This is why it’s important to keep reading the machine vision blogs. You never know quite what you’ll learn. (And kudos to Adimec for providing consistently good content.)

Linescan alternative

I know machine vision companies are all in business to make money, but Stemmer Imaging might be taking that just a little too literally. The video below shows them using the new KD Series Contact Image Sensor (CIS) from Mitsubishi to scan Euro notes.

Ignoring the dubious legality of such practices, I think the CIS is a very interesting product. I’ve always felt linescan cameras to be a poor method of imaging large webs, because the lens forces an angled view. (Yes, going telecentric overcomes that issue, but oh the cost!) Instead, the CIS is effectively the same kind of scanner we use in copiers and, well, scanners. So it looks directly at the surface being imaged, and not from an angle.

I have no information on cost, though I doubt it is in any way cheap, but I expect the good folks at Stemmer Imaging would be pleased to help. Meanwhile, enjoy the video.

It’s smart and it’s linescan

Here’s an interesting product, one that I intend to learn more about. One Box Vision of Clonmel, Ireland, has launched a linescan smart camera.

The Astro Vision System is available with sensors from 2k up to 12k, but what I find especially interesting is the software: the camera comes with Vision Builder AI from National Instruments.

I’m a fan of VBAI, as we NI fanboys call it, because it has a host of tools from the LabVIEW Vision Development Module and it’s simple to use. (Alright, I find the state machine concept hard to get my head around, but I’m a slow learner.)

The only downside I’m aware of is that VBAI tends to be expensive, but perhaps One Box Vision has done a good deal with NI. I suppose there’s only one way to find out …

CMOS and GigE

I’ve been reading about Basler’s racer linescan cameras. They’re pretty interesting. I hadn’t appreciated that they are both CMOS-based and GigeE. That’s a combination that yields some interesting benefits: less heat generated and no high-end framegrabber or expensive CameraLink cable required.

And where did I learn this? From “The Benefits of Modern CMOS Sensors in Industrial Line Scan Cameras”, available as a pdf download from Basler’s Document Downloads page. (Name and email required, but it is worth it.)

Now obviously, Basler’s White Paper isn’t exactly impartial, but it is well-written and filled with technical “meat”, so I suggest you take a look.

Color linescan camera options

Linescan imaging is complicated, color machine vision is tricky too. Putting the two together sounds like something only the bravest (or most foolhardy) vision engineer should attempt. Yet there are times when it has to be done.

Anyone needing to dip a toe in these murky waters would do well to learn more about the camera options. To that end, Dr. Xing-Fei He of Teledyne Dalsa authored “Trilinear Cameras Offer High-Speed Color Imaging Solutions”, published in the May 2013 edition of Photonics Spectra.

This compares and contrasts the three types of color linescan camera, giving the potential user an understanding of what to look for. Of course, price is left out of the article, but rest assured it correlates with performance, though not necessarily in a linear manner.

Happy (color) scanning!

Clever

Machine vision is all about solving problems: that’s why we love it so much. (Well it isn’t the money, that’s for sure!) And looking at how other people solve problems is a good way to generate ideas for those on our own desk. So take a look at “Linescan Camera System Scores a Hole in One” on the Vision Systems Design website (September 1^st, 2012.)

Yes, it’s a golf-related application, but as Andy Wilson notes, don’t let that distract you from what’s going on, vision-wise.

This is a three linescan camera system that locates and inspects print on a spherical object, (a reflective, dimpled one at that,) and then performs a defect inspection. Andy provides a link to a movie of the system in operation and gives considerable detail about how it’s done. There are also some good photos and diagrams.

Overall, this is a great article with enough detail to make it educational rather than it just being a marketing piece. I would however have liked to learn more about the lighting. It strikes me that was a non-trivial part of the challenge. And on a technical note, I was a little surprised by the way in which the cameras are mounted. I would have anticipated some vibration issues, but I have to conclude that wasn’t the case, since the system is in operation. (Click the link above to see what I mean.)

Thanks Andy, for making a positive contribution, and keep up the good work!

Lining up the linescan cameras

I’ve done a few web inspection projects that needed an array of linescan cameras, though I suppose, strictly speaking, it’s a 1D array. In every case, alignment was an absolute PITA . (If you don’t know that acronym, Google it.) So you’ll understand why I read and re-read “Custom Calibration Supports Linescan System Design” on the Vision System design website.

If you use the link I provided, you’ll find a detailed discussion of how two companies worked on a method of simplifying linescan camera alignment. There were two major components of this: a calibration target that produced data for tweaking camera positions, and a five degrees of freedom camera mounting system. If you’re working with multiple linescan cameras, I encourage you to read this very carefully.

You might also notice that the article is dated December 1^st, 2011. I can’t think how I missed it first time around, but I am very pleased Andy Wilson (the Editor of VSD) has taken to providing encore presentations of the most interested articles published. Without that I might have been forever struggling to line up my linescan cameras.

A better linescan light

I had the misfortune recently of watching an engineer set up a light for a linescan inspection system. If you’ve ever had to do this you’ll know that it’s far from easy. The angle of the light is critical to get the required contrast on the target, the working distance has to be right to minimize the line width and maximize the intensity, and the line has to align perfectly with the sensor in the camera. In short, there are just too many degrees of freedom.

This is what first drew me, like a moth, to the Corona II from German light and camera manufacturer, Chromasens. Instead of a rod lens, this uses a mirror to create the narrow focused line. And to make life easier for the integration engineer, the light has flat mounting surfaces with the mirror directing the beam out at a known and fixed angle.

As all you mechanical types will know, it’s much easier to construct mounting brackets and surfaces that are flat, square and parallel than at some complex angle, so this feature of the design seems a simple yet useful advance.

Another point I really like is the ability to control the output of the light automatically. Using what Chromasens call an ““Illumination Setup Tool” it’s possible to have the output altered in response to the image quality. This way the impact of dust on the light cover or reduced LED output (yes, it does happen,) is automatically compensated and the vision engineer gets fewer service calls in the middle of the night.

I doubt these lights are cheap, but this might be one of those cases where you spend more to save more. And that includes saving on installation time.

What can TDI do for you?

The TDI in question refers to the Time Delay Integration linescan cameras that Dalsa launched a few years ago. Intended to overcome linescan’s hunger for light, these have a multirow sensor that in effect tracks a region of a web. This gives the effect of a longer exposure time, so letting you run the surface to be inspected at higher linear speeds.

Now realizing that my opening paragraph may have done more to confuse than educate, let me steer you to an article that explains the benefits of TDI cameras by way of a real-world application. “Automating Solar Cell Inspection,” published February 13^th 2012 on the SolarNovus website, is an article from Teledyne Dalsa describing the use of TDI in PV inspection.

This article is interesting for a second reason too. One of the more successful techniques in PV panel inspection is to use IR backlight. Basically, the light shines through the silicon, highlighting cracks and other defects. Unfortunately though, camera sensors have fairly low sensitivity to the near IR, forcing the use of longer exposure times. So with the TDI camera discussed in the linked article Dalsa have increased the IR sensitivity. I think that’s what people call hitting two birds with one stone.

Now back to my question: what can TDI do for you?

The Basler approach to product naming

Britain’s Jeremy Clarkson recently described the MacLaren MP4-12C supercar as sharing its name with a photocopier, and his audience got the joke immediately. Sexy products like supercars should have sexy names: which would you prefer: Aventador or MP4-12C?

I think this also applies to more mundane products like machine vision cameras. “MQ022MG-CM” is an engineering designation that may do a great job of describing the product, but it’s unlikely to lodge in anyone’s cerebellum.

Basler seems to get this, which is why they name their cameras, using words such as Ace, Pilot, and now “racer”. AVT get it too, basing their naming strategy on fish – Pike, Marlin, Guppy and so on. These are all product names that will stick in the mind: when I’m asked to suggest a camera I may not recall the MQ0-12C or whatever it is but I will remember “Stingray” or “Racer”.

The “racer” is an interesting new product. Described as “cost-effective” (which I imagine means “cheaper”,) this is the start on a new linescan family. It’s built around a CMOS sensor and is available with either Power-over-CameraLink or GigE interfaces. The latter of course saves a few hundred bucks on a framegrabber, though whether that’s negated by a price premium over the PoCL version I couldn’t say.

What I will say though is that I’m likely to remember the Racer next time I’m asked to suggest a camera while I doubt the DLC-2048-48-CL (yes, I made that up,) will spring as readily to mind.

Learning from others

There’s always something to be learnt by looking at how someone else solved a problem, and a great example of that comes from the October edition of Vision Systems Design. Under the delightfully alliterative heading of “Detecting Defects in Dinnerware” (October 1^st, 2011,) comes a highly detailed description of a sophisticated inspection system.

I don’t want to steal author Dan Milkie’s thunder, (or VSD’s advertising revenue,) by repeating the story here, but let me explain why you should take a look.

The article describes an inspection system developed by Coleman Technologies of Newton Square, Pennsylvania, that performs both 3D and linescan imaging. There’s lots of detail on how both are done, including an excellent description of the image processing performed. If you have any interest at all in surface flaw detection algorithms, this should be a must-read. If you visit Coleman’s website you’ll also be able to view a movie of the system running in the development shop.

Learn from what other people have done.

Keyence goes linescan

As far as I know, the last machine vision company that attempted to make linescan imaging accessible to the regular user was DVT, and that wasn’t hugely successful, so I think it’s pretty big news that with their new XG-8000 product, Keyence is moving into linescan imaging.

The XG-8000 is actually the vision processor unit, but it will take a linescan camera, two if you also buy the expansion module. As with all Keyence vision products, the cameras are proprietary, meaning that you can’t plug in your Dalsa or Basler cameras. But there are some interesting features.

In terms of resolution, they’re offering 2k, 4k and 8k sensors, all of which are CMOS. The smaller sensors take a C-mount lens while the 8k takes a special M40 lens. Going to a C-mount format makes the cameras smaller than most linescans, and also permits a shorter working distance, both of which might be useful when space is tight.

No word on pricing - in fact at the time of writing the XG-8000 isn’t even on their website – but my guess would be around $15 to $18k. But I am guessing! That makes it expensive for a single camera configuration, but if you need two cameras the economics become more attractive. I imagine that the Keyence linescan cameras would be pretty much plug-and-play, which could be quite a time saver, and it also saves you from having to buy a framegrabber.

In terms of software and vision tools, the last Keyence system I played with was quite impressive, so I have no reason to think this will be any different. One other benefit I see is that while most linescan systems need some programming expertise, Keyence doesn’t.

In short, if you want to implement a linescan system quickly, and you’re not a skilled C++ or VB programmer, this might be a good product to consider.

The best way to skin the cat?

Sure, we know there are many ways to solve a given vision problem (“skin the cat”,) but is there ever a ‘best’ way? Well when it comes to web inspection I think Thor of Scorpion Vision has certainly hit on a smart idea.

Under the heading of “Scorpion 3D Surface Defect App” Thor describes a triangulation-based 3D approach to web inspection. There’s also a nice little animation to make his approach clear. What I like about this is how it eliminates the effects of varying surface reflectivity and inconsequential marking.

Of course, if it’s surface marking you’re after you might want to go with a more conventional web approach. A short post on the Vision Systems Design website alerted me to one company offering just such. This is Slovenia-based Wise Technology, who has a system called “Wise Scan.”

Technical details are rather sparse, but as best I can tell it’s a fairly conventional web system. That doesn’t mean it’s no good; it’s probably perfectly good for many applications (and perhaps quite price-competitive too,) but I feel that Thor is adding something extra.

Now, how about combining the 3D with regular web inspection? That would yield a mass of data about the surface, perhaps increasing robustness too. Any venture capital folks interested in backing me?

How to get the salesman to call

Do you ever find it difficult to get the attention of a salesman (or woman)? I know I do, but now I know why. The May 2011 issue of Vision Systems Design has the answer.

If you read “Flat-Panel Color Filter Inspection” you’ll learn about a web inspection system that uses 25 Piranha 3 12k linescan cameras, each connected to its own framegrabber, each in turn sitting in its own PC. That’s one heck of a lot of cameras, and a very nice order for Dalsa. I’m pretty sure that when Taiwanese integrator Utechzone gets on the phone to Waterloo, Ontario, those friendly Canadians pay very close attention.

The system sounds fascinating, but I’d love to see a movie of it in operation. If anyone from Utechzone happens to reading this, any chance you could post something on YouTube?

Meanwhile, I now know how to get salespeople to fawn all over me: just tell them I have a quarter of a million dollars to spend.

Line scan screamer

A note came across my desk the other day informing me that Dalsa have introduced a pair of Piranha 3 line scan cameras. (For all I know they’ve been on sale for a while, but I’ve only just learnt about them.) There are three features of these cameras that I find interesting: the resolution, the speed and the pixel size.

Resolutions are 8k and 12k, which for the user means either higher resolution or fewer cameras for a web. Of course, a wider field of view can also mean more optical distortion, and more pixels means more bits to process, so speed can become an issue.

And talking of speed, these babies are fast! The 8k has a line rate of 33.7kHz while the 12k manages 23.5kHz. That’s a whole bunch of pixels to process every second. (The 8k Basler Sprint delivers a line rate of 70kHz, but they don’t offer a 12k line scan camera, to the best of my knowledge anyway.)

Now what about pixel size? Well if you download the Piranha 3 datasheet, (registration is required,) you’ll see that the 8k sensor features 7µm pixels while the 12k has pixels 5µm in size. This keeps the two sensors approximately the same length, but what does it mean for imaging?

To answer this, in part anyway, Dalsa have provided a graph on the datasheet showing the responsivity of each sensor. This tells us that the 8k sensor with the larger pixels is about 30% more sensitive to light than the 2k with the smaller pixels.

Surprising? Well it shouldn’t be. A 7µm pixel has almost twice the area of one measuring 5µm, so naturally, it catches more photons. And that should raise a flag for those of you drawn to a 12k line scan sensor: it’s going to need an awful lot of light if you want to run it at its max speed.

Machine vision in the mailroom

OK, it’s not the mail room but this press release about vision in a DHL parcel distribution center is pretty interesting.

Making a long story short, DHL have thrown out bar code readers in favor of “auto-focus line-scan cameras” from German web inspection specialist, Vitronic. I was intrigued by the idea of an “auto-focus line-scan camera” so I spent a little time on the Vitronic web site trying to learn more.

The cameras referenced in the press release are VICAM-ssi2 models. These are interesting because they’re actually built by Vitronic; I had expected a Basler base at least. Unfortunately though, I could find no reference to an “auto-focus” capability, so I’m left wondering, how do they do that?

A 4-sensor line scan camera

I hear through the grapevine that JAI are launching a new color line scan camera. Unlike existing models of color line scan, which use either a bayer filter over the CCD or 3 sensors with individual color filters, this uses JAI’s prism technology. The major benefit is the superior color registration that results from a common optical path. This eliminates the alignment problems that make color line scan cameras such a pain to use.

Incidentally, the camera is available in only a 2k format, but the CCD sensors cover Red, Blue, Green and Near IR. This should make it useful for inspecting organic materials where IR can help uncover more data than is evident to the human eye. For an example of where this can be useful, take a look at this page on the JAI site about the similar multi-spectral AD-080 camera.

As for the LQ-200CL, which is what they’re calling this new camera, at the time of writing there are no details on the JAI site, but I’m sure that will change soon. Also absent is any pricing information. It won’t be cheap, but judging by the pricing of the AD-080 range I would expect this to be around $3,500.

And this is a 100 level class?

For my non-US readers, let me start with an explanation: Universities in the US rank their academic classes by three digit number where the leading digit signifies the difficulty of the class. Thus a 100 level class is generally taken by freshmen (first year students,) while a 500 level class is typically only encountered while studying for a Master’s degree. One consequence is that any introductory level is generally described as being “one-oh-one” as in Economics 101, or perhaps Machine Vision 101.

I start with this preamble because those of you who receive the print version of Quality Magazine, with the Vision & Sensors supplement will find, under the heading of “Machine Vision 101” in the May 2010 edition, an article titled, “Color Goes Mainstream.” (If you just use the web link you’ll notice the “101” subheading is absent.)

The article, penned by Henning Tiarks of Basler, provides a detailed discussion of the various flavors of color line scan, and in particular, addresses the challenges of aligning tri-linear color line scan cameras.

It’s a good article, and if you really need to acquire color line scan images, it should be required reading, but it is most definitely not 101 level. Line scan machine vision is complicated, and color line scan imaging is really complicated. Do not attempt this for your first machine vision project.

Linescan camera basics

Linescan camera are a very different animal to area or matrix cameras. For instance, how do you quantify the frame rate of a linescan camera? And what’s with all the dual tap/quad tap output stuff?

The spec sheets will answer these questions poorly, if at all, so you need a source of clear, yet detailed information. I recommend reading “PC-Based Line-Scan Imaging Systems” published on the Adlink web site. This paper, illustrated with lots of helpful figures, explains the details in a clear and simple way, so clear in fact that I could understand it.

In fact there’s only one question I didn’t get answered: should I be writing “line hypen scan,” “line space scan,” or one word – “linescan”?

A linescan camera for only $50

Yes it’s true, you can buy a new linescan camera for just fifty bucks. There is of course a catch, or perhaps it would be better described as a limitation: the sensor has just 128 pixels.

That will probably exclude it from the more challenging web inspection applications, but I can imagine more than a few situations where I need to monitor a narrow strip that moves beneath my camera – boot lace inspection, for example!

Interestingly enough, the target market for this budget cam is robotics enthusiasts – those technogeeks who spend their spare time building autonomous vehicles. I’ve read no end of blog postings where such folks attempt to give their creation stereo vision, but this is the first time I’ve seen line scan for amateurs.

If you’re interested in learning more, you should visit www.parallax.com. You might also like to browse the “Bot Thoughts” blog, which is where I first came across the TSL1401 Linescan Imaging Sensor.