An Introduction to Machine Vision Systems
Machine vision systems are a set of integrated components that are designed to use information extracted from digital
images to automatically guide manufacturing and production operations such as go/no testing and quality control processes.
These systems can also play a role in automated assembly verification and inspection operations through their ability to
guide material handling equipment to position products or materials as needed in a given process. They have wide applications
across different industries and can be used to automate any mundane, repetitive tasks that would become tiring to a human
inspector or operator. The use of
automatic vision measuring
machine allows for 100% inspection of products or parts in a process, resulting in improved yields, reductions in
defect rates, increased quality, lower costs, and greater consistency of process results.
How Machine Vision Systems Work
To understand how a
manual vision measuring machine
works, it may be helpful to envision it performing a typical function, such as product inspection. First, the sensor detects
if a product is present. If there is indeed a product passing by the sensor, the sensor will trigger a camera to capture the
image, and a light source to highlight key features. Next, a digitizing device called a frame-grabber takes the camera’s
image and translates it into digital output, which is then stored in computer memory so it can be manipulated and processed
by software.
In order to process an image, computer software must perform several tasks. First, the image is reduced in gradation to a
simple black and white format. Next, the image is analyzed by system software to identify defects and proper components based
on predetermined criteria. After the image has been analyzed, the product will either pass or fail inspection based on the
machine vision system’s findings.
Measurement functions of the
large-stroke
coordinate measuring instrument are done through the comparison of a recorded dimension from a digital image against a
standard valve to establish a tolerance or to determine if the observed value of the dimension is within acceptable levels of
tolerance as called for in the design specification for that part.
Video Motion Quality (VMQ) evaluates the relative motion quality of the distorted video generated from the reference
video based on all the frames from the two videos. VMQ uses any frame-based metric to compare frames from original video and
distorted video. It uses the timestamp of each frame to measure the intersection value.
VMQ measuring machine combines the comparison value with the intersection value in the aggregate
function to produce the final result. To explore the efficiency of VMQ, we used a set of uncompressed original videos to
generate a new set of encoded videos. These encoded videos are then used to generate a new set of distorted videos that have
the same video bit rate and frame size, but the frame rate is reduced.
In modern machines, the
gantry type vision measuring
machine superstructure has two legs and is often called a bridge. This moves freely along the granite table with one
leg (often referred to as the inside leg) following a guide rail attached to one side of the granite table. The opposite leg
(often outside leg) simply rests on the granite table following the vertical surface contour. Air bearings are the chosen
method for ensuring friction free travel. In these, compressed air is forced through a series of very small holes in a flat
bearing surface to provide a smooth but controlled air cushion on which the CMM can move in a near frictionless manner which
can be compensated for through software. The movement of the bridge or gantry along the granite table forms one axis of the
XY plane. The bridge of the gantry contains a carriage which traverses between the inside and outside legs and forms the
other X or Y horizontal axis. The third axis of movement (Z axis) is provided by the addition of a vertical quill or spindle
which moves up and down through the center of the carriage. The touch probe forms the sensing device on the end of the quill.
The movement of the X, Y and Z axes fully describes the measuring envelope. Optional rotary tables can be used to enhance the
approachability of the measuring probe to complicated workpieces. The rotary table as a fourth drive axis does not enhance
the measuring dimensions, which remain 3D, but it does provide a degree of flexibility. Some touch probes are themselves
powered rotary devices with the probe tip able to swivel vertically through more than 180 degrees and through a full 360
degree rotation.
Height gauges can be used to determine an object or workpiece’s height with
extremely high accuracy and precision. These precision measuring instruments also provide marked locations on an item
relative to one reference plane for subsequent use.
Center-line distances, internal/external diameters, and step heights are some of the different measuring tasks that can
be carried out by high-specification digital height gauges.
They claim consistency of ±0.0001 inch and can be extremely precise up to 0.001 inches. Of course, the consistency and
precision of such instruments still depend on their overall quality, so it’s essential only to source one from websites of
reliable manufacturers.