Product category:
Vision and scanning systems
News Release from: Cognex UK | Subject: Digital camera systems
Edited by the Manufacturingtalk Editorial
Team on 28 May 2001
Vision devices speed up robotic assembly
at Volvo
At the Volvo K?ping factory, seven robots assemble 17 components in 30 seconds. They use digital cameras and advanced, patent-applied image processing technology.
At the Volvo Koping factory, seven robots assemble 17 components in 30 seconds This is possible since they use vision technology in the form of digital cameras and sophisticated, patent-applied image processing technology
This article was originally published on Manufacturingtalk on 6 Jun 2001 at 8.00am (UK)
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The functionality of the robots has been considerably enhanced, and they can pick components right off the pallets.
This improves productivity, reduces costs and raises quality of the Volvo S80 model.
The transmission division at Volvo Car Corporation Components AB in Koping delivers finished front wheel assemblies etc.
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to Volvo in Gothenburg.
Each front wheel unit consists of a number of components which are assembled once they have been manufactured or bought in.
Assembly is either done by hand or by means of robots.
Hand assembly is monotonous and heavy.
It is also a very simple task which one preferably wants to avoid giving to people to do.
Ordinary robots can do the same task day after day without tiring, on the other hand.
This assumes that the components which are to be put together are accurately laid out and prepared, however.
But robots are "blind" and can not see if anything goes wrong, or if the quality falls below certain set limits.
Using vision technology, one can literally give the robots eyes, and get them to do more advanced operations with greater precision.
The transmission division at Koping wanted to use this technology when they started to supply front wheel units for the new Volvo S80 model.
Production started a couple of years ago.
The vision technology Volvo, Koping now uses is based on a patented method, Patmax, supplied by the Cognex company in the USA.
The method comprises an image processing technology which recognises the geometric shape of an object.
By this means, the vision system can localise a photographed object even if it has changed position, or if the distance has increased or reduced compared with the reference image.
This is hardly possible with other vision technologies.
In Volvo's case, the robots and automatic handling machinery are to pick up and assemble 17 different components to create a complete front wheel unit for both near-side and offside wheels.
The components come directly from the suppliers' special packaging, and are not fixed in pre-determined positions.
This means that the robots must be able to choose both left and right hand components depending on what needs to be assembled.
They should also be able to get the correct component, even if it lies in a different position compared with the previous component.
This, in its turn, means that the robots may have to twist and turn the component and then place or assemble it correctly.
The system must also be able to give signals and stop handling if deviations exceed limits which the operator has set.
"Each vision system is controlled by a personal computer.
A special computer system makes sure that the different systems can communicate with each other.
Using the same system, the operator can also monitor the seven assembly stations included in the assembly system for front wheel units for the Volvo S80 model" says Anders Boman, who is one of the project managers.
A robot, which is controlled by the vision system, can pick components straight from the pallets containing the components to be assembled and then put them on the robot station.
Each robot is surrounded by a wire fence to prevent people from getting too close to the robots.
The solution to this problem is functional communication between all units included in the production line, and above all, that the robots are given good information about the components to be handled.
For this reason, each component the robots are to handle is photographed.
This information then controls the way that the robots are to pick and turn the components from their original positions.
The unique feature of the Cognex vision system is that it can localise and measure objects with great position, even if they have changed position and height - and size as originally seen by the camera - compared with the reference information.
The vision system recognises an object by dividing it up into geometric shapes and measuring shape, dimension, angles etc.
A square is seen as four lines, for example, which have a particular spatial relationship with each other.
This relationship will be the same even if the object has changed position.
The system thus recognises an object, even if it is in a different position to earlier, or if it is at a lower level and thus looks smaller.
This is practically impossible in other systems; in these, the object must be in the same position as the reference image to be recognised.
The Cognex vision system obviously has to start off with reference information before it can start to be used.
For Volvo, this meant that the operator had to start by putting in images of the objects to be handled by the robots.
Co-ordinates and angles are then added to the images, to form references.
In addition, the operator then has to put in information about the height of the uppermost component in each pallet, for example.
The height information can be updated from two directions, either via the robot after height seeking, or using the height seeking function built into the vision system.
Using these calibrated images and data, the vision system then makes comparisons with the images which are subsequently taken of the components which the robot is to pick from the pallets.
The deviations form the input material for the movements, which the robot needs to do to collect the correct component, and the rotations needed to be done before the components are put on the robot station.
Each robot with a vision system is connected to four digital, black/white cameras.
These are installed above the pallets containing the components to be installed.
Two of the cameras are used to photograph left-hand components and the other two are used for right-hand components.
In Volvo's production line, assembly starts when the first robot station picks a steering knuckle from the pallet.
The pallet has knuckles for both left and right wheels.
If the robot needs a steering knuckle for the right wheel, the two right-hand cameras take a picture each of the steering knuckle.
One of the images is then stored in the memory, for comparison with the reference image and other references.
The comparison gives information about how the desired steering knuckle is oriented in the pallet, and controls how the robot is to grasp and turn the steering knuckle, before it finally puts it in the correct position on the table of an automatic turntable (turret), where some tasks are done automatically.
Using the vision system, the robot can not only pick up the steering knuckles.
When the first layer of components has been picked up, the robot also removes the packaging and continues with the second layer.
When the pallet is empty, the robot puts the packaging back.
The empty pallet is taken away and a new pallet is brought in, which the robot can start to pick from.
"The alternative to using a vision system would be to either re-load the components manually onto a pallet to be fed into the robot.
But since the components are so heavy, it would be just as simple to transfer them directly to an assembly pallet.
This means in practice that you would do the work manually.
Or you could get the supplier to supply the components securely fixed in special packaging, so that they could be picked directly, using co-ordinates.
Both alternatives would be considerably more expensive than the vision technology we chose.
In practice, this is just not an alternative," says Anders Boman, one of the project leaders who works with the vision system in the transmission division at Volvo in Koping.
Once the robot has placed the steering knuckle in the turntable, the turntable continues by installing a ball joint, which is then screwed to the steering knuckle.
After this, the robot takes the steering knuckle with the ball joint assembled - without vision since the position is securely determined - and puts it on a pallet which is then transferred to the next robot cell.
A further two robots use vision technology.
The second one picks up the brake disk and hub, which comes from a supplier in Floby, and charges the component onto a pallet for further processing.
The vision technology is needed here, to orient the hub in a special alignment so that the steering knuckle and shield can be paired together.
The robot in the third vision system works in a similar way, where it has to handle and align a brake calliper, which is used in the wheel unit.
The finished, assembled front wheel units are given a bar code and are then put into empty pallets.
In this way, each unit can be traced, which is important considering the EU quality requirements, and to provide a smoothly functioning logistics system for the assembly factory.
A total of five robots work in an area of only 5 X 50m.
In this area, they assemble the 17 components included in a front wheel assembly.
The entire assembly cycle takes half a minute.
This means that a component is assembled ever two seconds.
To get the system to function as a unit, both the seven robots and the three vision systems can communicate with each other via an integrated network system with PC and PLC functions.
This means that it is quick and easy to re-set the production flow and still have full control of the precision and quality of all operations.
Each robot works in a cell, surrounded by a fence to prevent people from getting too close.
The people responsible for construction and installation of the entire robot system, including the vision systems, is ABB Flexible Automation in Vesteras.
Lennart Thiede, who was the assembly supervisor for the Volvo, Koping installation works there.
For him, it was the first time he worked with Cognex and vision technology.
"But it will probably not be the last time.
We are very pleased with both their technology and their knowledgeable personnel.
Everything has worked very well," he said.
ABB set up a complete installation in their own premises before the plant was installed at Volvo, Koping, where the equipment could be approved by Volvo for delivery. Request a free brochure from Cognex UK ...
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