26
Mar 2015

Here, we review the main features and aspects of 3D scanners to consider before purchasing.

 

Firstly, the scanner technical specifications will probably be the most relevant information to look at. This is resolution, accuracy and precision of the scanner.

 

Resolution – the higher the number is the smaller the distance between points. Manufacturers will provide the scanner resolution in megapixels, but we need to check the minimum point distance that we will get in the point cloud (take into account that a multi-area scanner will offer different point distances for different working volumes with one single camera resolution). Now, we only need to know the size of the smallest feature we need to capture in the parts to be scanned. As a rule of thumb, we will look for a point distance 3 or 4 times smaller than the size of this feature.

 

Accuracy and precision are well described in this article, so I will not cover them here. Just recall you that the values the supplier gives must be calculated according to a standard or norm. The VDI 2634 recommendation can be seen as a de facto standard in the industry.

 

Precision is far more important than accuracy because, if a scanner is repeatable, accuracy errors can be compensated or corrected. And accuracy and precision are not always directly related to resolution. This is, a 5Mpx scanner could be more accurate and/or precise than a 16Mpx one.

 

The tolerance requested in our measurement will drive the need for higher or lower accuracy. Smaller tolerance will require more accurate scanner. It is difficult to give an exact number here, there are a number of norms that explain this relationship with more or less complicated formulas. For the sake of simplicity, as a rule of thumb, the NPL (National Physical Laboratory of London) in his paper “A National Measurement Good Practice Guide” states that accuracy needs to be 10 times better than the tolerance one is manufacturing to.

 

Is the 3D scanner based on a single or multiple camera system? The geometry of the scanned results can be better with single camera systems, because possible errors due to overlapping scans are reduced.

 

Physical design and construction is a key factor – the more robust, the better. Durable materials such as carbon fibre are typically used in scanner manufacture, to offer strength regardless environment conditions combined with light weight for portability (if required).

 

Portability is an aspect which may be significant, depending on intended use. Will the scanner be a permanent fixture based in an office, or will it be used at remote sites? Many systems come with a carrying case for convenience and safety when transporting the device and accessories. Vibration control features are valuable – if vibration is detected by the scanner system while a scan is being carried out, the measurement is repeated, to avoid errors.

 

Automatic calibration is another positive feature. Proper calibration is essential to maintain reliability and quality of the scan results. The device may have a ‘single click’ option in the software or a push button, to carry out an automatic calibration when powered up and particularly after dismantling and reassembling.

 

Expandability and compatibility with existing systems is important. Consider whether the scanner model will integrate with operating systems such as Windows 7 or 8, Linux etc. Additionally, if any existing proprietary 3D scanning software is already used for ‘point cloud management’, check the compatibility of the proposed new hardware with this. The scanner’s detailed specifications may list compatibility with leading software such as Polyworks®, or Geomagic®.

 

Moving from software considerations to hardware, it can be advantageous (depending on the type of work envisaged) to have an adjustability option for the light source. Some scanning systems offer a scanner light source which is variable between white and blue, for instance.

 

Other points to note include advanced software features such as faster scanning, along with recognition of differing light conditions and reflection (the differences between black, white and shiny surfaces), avoiding the need for consumables such as matting spray – and helping to prevent reflection errors. Hardware monitoring functions to count lamp hours are also useful to help plan maintenance.

 

To conclude, every 3D scanner has its own specifications but not all of them can fit your expectations. Be sure the one you select answers your needs and allows you to handle your application.



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