visual line tracking, studia, przemysłowe systemy wizyjne

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Visual Line Tracking
Application Overview
& Issues
Machine Vision for
Robot Guidance Workshop
May 5, 2004
Donald DeMotte
Senior Staff Engineer
FANUC Robotics America, inc.
Visual Line Tracking
Vision Show East
May 5, 2004
1 Background
Machine vision has been used with robots doing line tracking for several years.
Typical applications include:
• Pick and Place of non-fixtured parts
• Sorting of non-fixtured parts
• Placement of parts onto fixtures on a moving conveyor
The typical system is:
The typical system has the following components:
1. Conveyor system with parts
2. Fixed Camera and Vision system
3. Industrial Robot
The typical application in the manufacturing environment does not have a high throughput or performance
requirement. Typically one robot with one camera can handle the line rates of 10 to 20 parts per minute.
Other markets (such as the distribution and packaging of consumer goods and food products) have
significantly faster rates (100 to 300 parts per minute) and require higher performance. In the past, selected
high speed or specialized robots were the only solutions available. The vision, robot, and computer
hardware performance has been increasing where these applications are now achievable and justifiable with
standard components.
But these applications present some different engineering problems and considerations.
Visual Line Tracking
Vision Show East
May 5, 2004
This paper will present:
• Component requirements for Visual line tracking
• Considerations for the engineering and analysis of the high performance visual line tracking
application.
The performance data that is presented is intended as a trend of what you might see. You must take the
conditions of the any proposed project and solution into consideration when using these guidelines. Other
aspects of vision and robot programming will have an impact on what can be expected from any cell.
The performance topics discussed include:
• Why scan time is Important
• Impact of # parts in Field of View (FOV)
• Impact of display/plot controls
• Impact of number of robots
• Impact of PC speed
• Considerations for FOV and conveyor speed
•
Maximum Throughput discussion
Visual Line Tracking
Vision Show East
May 5, 2004
1 System Components
The typical system has the following components:
• Conveyor system
• Fixed Camera and Vision system
• Queuing System
• Industrial Robot
1.1 Conveyor System
The conveyor system must provide a good background for the vision system. Webbed conveyors (as
shown in the picture) can present vision problem, especially if the conveyor and part colors are similar. In
this example, the part had to be placed on a mouse-pad to achieve acceptable training results.
The conveyor must be reasonably consistent in the actual movement. That is to say, there should not be a
lot of slack in the drive mechanism so that the conveyor jerks forward at times.
It must also provide an encoder input (motor position) so that the conveyor position of the time of the
vision acquire can be recorded. This is critical to the accuracy of the part pickup.
Visual Line Tracking
Vision Show East
May 5, 2004
1.2 Fixed Camera and Vision system
The vision system has the following requirements:
• Progressive scan camera
• High speed communication method to robot
• Calibration software to match the vision frame with the tracking frame of the robot.
• Means to acquire conveyor position at time of vision acquire (1 of two methods)
o
Hardware pulse at the time of the vision acquire (to trigger a robot program)
o
Direct reading of encoder
A progressive scan camera is important to reduce the impact of a moving part. With a regular camera, the
image can appear blurry due to the speed of the part. A higher shutter speed can reduce the impact, but will
not totally eliminate it. Depending on the vision algorithm, the slewing of the part could impact accuracy
and fit scores. It would be like trying to find an object in a blurry image.
See the image below (at high magnification) for the impact of not using a progressive scan camera.
Visual Line Tracking
Vision Show East
May 5, 2004
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