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Computers

When selecting a PC for an imaging application there are many factors that need to be considered in order to ensure that the solution chosen delivers the performance needed, combined with both long-term reliability and stability of supply.

In this section we will cover some of the system features that are important when specifying a PC and a supplier for a vision system.

Only a few years ago compact and embedded PCs just did not have the performance needed for a machine vision system. This meant that PCs for machine vision often standardised on the 19" rack mount approach with server grade high-performance components installed.

In recent years we have seen significant reductions in the power to performance ratio. Very capable fanless and compact industrial PCs without internal cables or internal moving parts can deliver per formance with high environmental specifications. They are suitable for both the harsh environments of the factory floor and the processing power required for imaging. As in most markets there is a wide variety of options and invariably you get what you pay for. Time and time again it proves to be a false economy specifying office grade PCs in an industrial machine vision system.

Recently, there has been a significant growth of non-Intel/Windows platforms in embedded applications such as networking, automotive and mobile phones. These ARM processors are now migrating into the machine vision market in high volume, low power applications. We are seeing machine vision cameras supporting the embedded MIPI interface and machine vision software vendors porting to these platforms. STEMMER IMAGING is embracing this change and providing support services and software modules to significantly reduce the time to market

Requirements

Selecting the right components can make a huge difference to the performance of a vision system and its long-term reliability, especially as a vision system is expected to handle very large amounts of data (images) in quick succession. Not all PC systems are well suited for these tasks and most off-the-shelf domestic computers often have never been stress tested with continuous high throughput of data. Leaving the interface architecture to one side, as this is covered in the acquisition section in detail, some of the key considerations when specifying vision computing hardware are listed below.

  • What is the maximum data rate that the system needs to handle?
    • Number of cameras / image size / frame rate?
    • Memory bandwidth required?
  • How many simultaneous images need to be held in memory for immediate access?
    • Memory required?
  • Does the system have to process this data at the same rate? *Combination of speed / number of processors / memory bandwidth?
  • Does the system have to record all this data to disk?
    • RAID: disk configuration, data rate?
  • What level of hardware redundancy is required to ensure data integrity?
    • RAID: disk mirroring, redundant power supplies?
  • Does the software support multi-processor or multi-core systems?
    • Number of processors and different configurations?
  • What level of reliability MTBF (Mean Time Before Failure) has to be achieved?
    • Consider the PC design including cables used or solid state disks.
  • What is the environment of the target location in terms of temperature, vibration?
  • Expected production start / life cycle?
    • Component obsolescence and supply security?
  • Mechanical considerations?
    • Housing size and design?
  • Environmental aspects?
    • Lead-free, PC fans/filters, electrical noise, EMC, etc.