Cameras

Understanding Back Illuminated Technology in machine vision

Until Hideo Yamanaka published his 2009  “Method and apparatus for producing ultra-thin semiconductor chip and method and apparatus for producing ultra-thin back-illuminated solid state image pick up device”.  The technology of back illuminating sensors was costly, complex and required further refinement to become a widely used sensor.  Yamanaka found that by rearrangement of the imaging elements, increased light could be captured and thereby improve low-light performance.  However, back thinning lead to a host of other problems such as cross-talk which causes noise, dark current and color missing between adjacent pixels.  Thinning also made the silicon wafer more fragile.

A traditional front illuminated camera is constructed to mimic the human eye; a lens at the front and photodetectors at the back, a back illuminated sensor arranges the wiring behind the photodiode substrate layer by flipping the silicon wafer and then thinning its reverse side so that light can strike the photodiode layer without passing through the wiring layer.

Front vs Back Illuminated CMOS

Front illuminated CMOS sensors vs. Back Illuminated CMOS.

Today back illumination technology has made some significant progress and BI chips are now available from several manufactures of Silicon Chip technology.  With higher sensitivity over a broader spectral region (deep UV to near IR) several industrial camera manufacturers are introducing back illuminated cameras.

These cameras are ideal for ultra-low light applications like Astronomy, Spectroscopy and biological imaging.  With back illumination, low light applications get increased Quantum Efficiency up to 95% and lower read noise at <2 e-rms.  When every photon counts a camera with a back illuminated sensor should be your one and only choice.

If interested in incorporating a back illuminated camera into your project check out the new .pco Panda 4.2 BI :  PCO. Panda 4.2 BI

 

 

 

 

Cameras

5 Reasons You Should Choose a 10 GigE Camera for your Machine Vision Application.

There are many types of Ethernet cameras available for machine vision applications. This is a brief introduction to Ethernet and why 10GigE cameras are attractive. Continue reading “5 Reasons You Should Choose a 10 GigE Camera for your Machine Vision Application.”

Cameras

What is the Best Machine Vision Camera for my Application?

How to select the right camera for your machine vision application?  I would like to present a brief description of the basic procedures that my company, Pyramid Imaging, uses when asked by our customers to determine the best camera for their application.  We’ve been doing this type of work for decades and have developed a simplified but reliable way to narrow down the broad array of possible cameras to a small group of possible candidates.

But, let’s talk about some basics.  We consider a machine vision camera as a camera that will be used to obtain images for an automated process.  We need a camera that has the right number of features that will allow us to control it properly and obtain the images that we require.

First and foremost is to understand the application’s goals.  Are we looking at an Inspection process looking at labels and barcodes, are we requiring Metrology to be done; that is, making accurate measurements on an item?  Maybe we are examining high speed events or do we just need “pretty pictures” for presentation purposes?

Application Goals

Once we truly understand the goal for using a machine vision camera we need to now list all of the application constraints.   We are now looking for the sweet spot in the constraint analysis in which the best camera will satisfy all the requirements.

Application constraints

There are literally thousands of cameras to down select to the one that will be best for your machine vision application.  The broad categories for these cameras include cameras that are:

  • Line Scan – 16K Linear array
  • Area Array – 80 MP and higher
  • High Speed – hundreds of thousands of frames per second
  • Analog (RS-170), FireWire, USB 3, GigE, Camera Link (CL) , Camera Link HS, CoaXpress

These cameras area all about bandwidth and cable length.  Remember that high resolution and high speed cameras need high bandwidth requirements!

You also need to know what lens mount the camera should possess.  These include:

M12, CS, C, F, M42, M75 Lens Mounts.

These are listed in order of increasing aperture. Remember that the bigger the sensor the larger the camera opening needs to be for a lens with a larger aperture.  Also, note that for a line scan camera using a linear array sensor the sensor’s length would be used to determine the largest image circle needed from a lens.  For an area array camera you would use the diagonal length of the imager.

There are also various features that might be required in a camera.  Features such as:

  • Selectable Regions of interest(ROI)
  • FPGAs
  • On camera memory
  • Many others

Here is a type of decision tree that can be considered when trying to select the best machine vision camera:

decision tree for camera

There are many factors to consider when trying to select the appropriate and best machine vision camera for your application.  First and foremost you need to analyze and reanalyze the goals for the machine vision application.  The next vital consideration is to use the best lighting and illumination to highlight the objects of interest.  You want to create as much contrast as possible between what you  want to see and try to make everything else disappear.

So, a quick set of steps for selecting the right camera would be to:

  1. Calculate Resolution- smallest detail in the field of view.
  2. Calculate the object or camera speed- determine best exposure time and frame rate to “freeze” the image.
  3. Encoder or speed sensor ?  If yes prefer line scan !
  4. Distance from computer or display ?  Resolution, Frame rate, Distance dictates data bandwidth , video protocol and cables.
  5. Time to record ?  Dictates amount of RAM and/or RAID storage.
  6. SWAP and other constraints ?  Prioritize
  7. Narrow down and sort camera list on priorities- features, cost, lead time, technical support, viability of manufacturer, etc.

Pyramid Imaging has been providing assistance to customers for decades on selecting the right cameras and other machine vision components.  Go here to see a small example of some of the projects in which we’ve been involved.

Pyramid Imaging  provides this very convenient tool that you can use to  down select cameras based upon certain specifications.  Just go to the camera selector and click on the specifications desired.

We’d be happy to provide you with our free assistance should you like to discuss your application with our experts.  Just Contact Us.