Pascal van der Krogt, Hugo Vader, Peter Verweij, Victor Reinders (Spring 2016)
3M is a worldwide technology concern that works in many areas. The company delivers adhesives, foils, sanding paper, power tools etc.
Project outline
A new type of sanding paper has been developed within 3M. This sanding paper has a seven times longer lifespan than the commonly used sanding paper. Users of this sanding paper are still throwing the paper away after a single normal lifespan. This problem should be solved by eliminating the human factor, the use of a robot. These robots will be rented to the customers of 3M.
The fixture, designed as a mount for the power tool, has several components that have to be redesigned. This has to be done in such a way that the fixture looks professional and is ready for demonstration at the clients so it’s able to sell.
Problem definition
A proper fixture is needed to absorb the pressure of the sanding machines on the workpiece. This fixture also acts as a connection to the robot. The fixture should be a plug and play solution.
Goal
A custom fixture should be developed to fit the sanding machines to the robot arm. This fixture should be able to use the right pressure needed for sanding.
Scope
- There should be a proof of concept of the fixture;
- The fixture needs to bend in both directions, up and down;
- The hinge should be more robust;
- The spring system needs at least two pressure stages;
- The pressure must be applied mechanically or with air pressure;
- The pressure required is between 50-300 gram;
- There must be an indicator to detect touching of the workpiece;
- The air intake must be integrated into the fixture;
- The fixture needs an adapter as a plug and play solution;
- The tool needs to be able to work in a dirty and dusty environment;
The solution
In order to get to a plug and play solution several parts had to be designed or redesigned. In the following part the solution to successfully complete this project will be given.
The robot used is a Universal robot, the UR5. This robot has a maximum payload of five kilogram. The fixture has a load of 1,5 kilogram and the pressure will differ from approximately 50 to 400 gram, this results in a maximum load of approximately 2 kilogram. So the strength of the robot should be sufficient.
Detection
There had to be a solution for detecting touching and measuring pressure on/of the workpiece, there is a feasible solutions that could be implemented into the system. There is chosen for a load cell that works with a strain gauge.
Due to assembly time and with the requirement to make the fixture robust there is chosen for type 2. The load cell has a range of 0 to 5 kilograms. Because the load will approximatly be 2 kilograms this range should be sufficient.
The loadcells will be programmed in the arduino board, this board sends a signal to the robot. The signal is an indicator on the amount of pressure applied on the workpiece.
Hinge & springs
The first design of the hinge is only able to bend in one direction, up. The requirements tell the hinge need to bend in two directions, up and down. In order to do this the hinge is redesigned. The hinge is used to absorb inequalities on the edge of the workpiece.
It is important to apply pressure on the workpiece with the power tool. In order to do so a counter pressure should be applied when the hinge starts to bend. This can be done by usage of springs. To keep the hinge robust a big axis and the use of torsion springs is used. The design is shown in the figure below. The axis is modular this is important to realize a plug and play solution. The hinge is printed so it can be tested quickly on the system.
Housing & electronics
The housing of the motor is designed in a way so the electronics fit on the power tool. The electronics that need to fit in the housing are the Arduino Uno board, the LCD screen, the load cells and the wiring. The design is shown in the figures below.
The electronics used to measure the pressure on the workpiece and to send signals depended on the pressure is all integrated in an Arduino Uno board. To show when the power tool is touching the workpiece a LCD screen is used. This screen simply shows the amount of pressure applied, so when the pressure is starting to change the power tool is touching the workpiece.
The housing is 3D-printed to be able to test after a short time span. The 3D printed housing filled with all components is shown in the figure below.
Integration on the robot
The complete system will be controlled by the robot, the Arduino sends signals to the robot that tells information about the amount of pressure applied. According to the signal the robot knows what kind of movement it needs to make. There are two options:
- Movement up/down: depending on the amount of pressure and the orientation of the sanding process. With this movement the robot is able to control the amount of pressure applied on the workpiece.
- Start sub processes: When the robots detects pressure it will send a signal to the air valve to open and to the vacuum cleaner to start.
- Emergency stop: The robot stops all movements because the pressure is too high or a collision is detected.
Conclusion
The conclusion is that the proof of concept is feasible. The pressure is applicable in every desired amount. The robot moves up or down depended on the pressure applied in this way the pressure is regulated. The only problem is the air pressure on the sanding machine, this seems not to be sufficient. The LCD gives the exact amount of pressure applied on the workpiece, the hinge works well on adapting to inequalities.