Fragile module handling and placement
For one of our customers we developed a service and installation tool that allows accurate placement of a very fragile module. The challenge lies not only in the 400kg mass of the module and the challenges for ergonomics. It is also the very limited space, various configurations, the required accuracy and the fragility of the module that needs to be handled.
Being in the heart of the customers machine this approximately 400kg module is very hard to reach. There are obstacles everywhere. Floor space is limited due to cables and ducts. And depending on the configuration of the factory the access point is either from the left or the right side. Also depending on the access point the obstacles in the floor are in different locations. What is left for the tool is a very irregular and limited space. So the layout of the wheels needed to be carefully chosen to accommodate both situations and the top table can rotate 180degrees to allow access from either side.
To the sides and the back there is only limited space but people are needed to release the bolts securing the module to the main machine. So these people need to gain access to the module while our tool is there I nan already tight space. That puts an even bigger restriction on the footprint and on the overall size of the tool. Unfortunately the support and access points are already frozen in the module design.
Being involved early in the module design would allow us to prevent the biggest issues and improve the handling of such a module, resulting in a more simple and less expensive solution.
But we like a challenge, so a maximum amount of (crawl) space needs to be achieved and the access to the interface bolts cannot be blocked by the tool. This lead to various discussions and concessions to get the most out of the tool without getting unacceptable ergonomic and safety issues.
All the challenges lead us to the part we value most. People near and partially under a 400kg module in a confined space is not something we take lightly. This needs to be safe in under all circumstances. So after an extensive risk assessment all factors of safety, failsafe’s and reliability checks are performed and meticulously implemented in the design.
All this is not yet challenging enough for us. So we get to the whole point of developing a tool. It’s primary function, so we continue with adding the functions but also more restrictions. That is to say. Our clients do. We are always having healthy discussions to challenge our clients to improve their machine and module design to make handling and access easier. However, concurrent engineering only takes you so far. Some things are just frozen in conceptual design and cannot be changed anymore.
So next challenge is the available height. The combined height of the tool and module may not exceed the available height under the machine. We were limited to 840mm of total height. This to avoid stripping more parts from the machine than absolutely needed. So that makes 700mm stoke for a 400kg and 500mm high module fitted in just 340mm of space.
The available is not just to get the lifting stoke in. The 340mm also should include ground clearance and other functions, such as leveling, force regulation, alignment and our 180 degrees rotation of the top table.
The floor is not absolutely flat, so we added a leveling function. Because clearance in the final approach is just a few millimeters and the 500mm height of the module gives a significant offset with even the slightest tilt. So adding an inclinometer with a digital display together with the mechanism to adjust the tilt in Rx and Ry allows the operator to adjust the levelness within the 5mrad specification. In addition and to avoid unnecessary damage to our module, the software of the lift registers the angle provided by the inclinometer and does not allow lifting and lowering unless the tilt is set within the 5mrad.
Nex feature is a load limitation implemented with the use of sets of preloaded springs. These springs are strategically placed w.r.t. the center of gravity of the module and are preloaded to only compress when the nominal mass of the module is exceeded. So when arriving at the top when the module needs ‘to be married with’ the main machine the sensors detecting the compression of the springs give the signal the final position has been reached. And because of the strategic spring positioning mentioned, 3 sensors ensure that all interface positions are touching and the lift automatically stops and signals the user ‘all is well’ to secure the module to the machine. And since we have these 3 sensors our lift has an additional trick up its sleeve. If a single sensor detects a certain offset that is too large w.r.t. the other 2, this is perceived by the software as a collision and the lift also stops indicating a warning for the operator.
This spring functionality also has the function to ensure the safe removal of the module. Our springs and sensors allow us to detect we have the module fully supported with the right amount of force.
Again the lift automatically stops when this position is reached and signals the user it is safe to remove the bolts securing the module. The user can do this without the risk of the module dropping or even lowering the slightest bit because we are pressing against it enough, but not too much (remember it is a delicate module) to support the full weight of the module with a calculated certainty.
Now that we covered all the other functions we need to get the job done without damage or danger we still need to fit the lifting itself in the space that’s left. A 2 stage spindle driven scissor lift is equipped is added. It is sunk between the wheels as close to the floor as we could get it. We added all the necessary failsafe’s such as a safety nut that only kicks in when the primary fails. Which should never happen given the factors of safety but with people so near and even under the module and no space to escape, there is no way we would take that risk. Using a high quality gearbox and servo motor with absolute encoder allows to have full control of the speed and position throughout the stroke of the lift. The lift slows down in critical parts of its vertical stroke. For example when it is about to reach the final position and clearances get smaller and smaller the lift slows down.
Visibility is poor and we want to at least keep people out of the way as much as we can. They could but we make sure they just don’t need to and also make sure they are not tempted to do so. There are guiding pins to ensure the module cannot deviate from its path. It cannot collide with its surroundings and it arrives within the catching range of its interfaces towards the main machine. Tilt is being monitored, collision detection is in place and the reduced speed is low enough to come to a complete stop before creating serious damage.