So after some testing moving the platform, we concluded that the wheels are too big for our platform. We weren’t able to move the platform quite easily and turning was a nightmare, so we went searching for a new set of wheels and that resulted in these wheels( see picture below).
These so called ‘ Breaking and locking casters’ are ideal for our platform, because of numerous points. First they are much smaller in size, hence the platform is much easier to guide. Second these wheels can be locked, not only the backward and forward movement but also the rotational movement. At last these wheels look much cooler on the platform :).
For the platform design, we first take stable into consideration. The platform include two parts, the shell frame and wheels. With the help of omnidirectional wheel with lifting device, we can at first put the platform into the ground in order to make sure the stable of device when robotic arm is painting. Meanwhile, if we want to move the platform, we just need to rotate the lifting device and the platform will rise up and can easily moved.
We started designing the spray mechanism by dividing the problem into smaller problems. These problems were holding the can, fixing the spray direction, pressing the cap and fixing the mechanism on the robotic arm. We decided to fix the nozzle and push the can to get the paint out, this way the distance to the nozzle is always a fixed distance. The first concept also involves a bench vice mechanism to hold the can and a pin to hold the cap. Furthermore an air piston is used to actuate the can.
First sketch of spray mchanism
After reviewing the first design we’ve made a few simplifications to make the mechanism easier to manufacture and more convenient to use. First of all we decided that using air pressure solely for the spray mechanism would be unnecessary. So we’ve decided to change this to an electronic system. We’ve also decided to fix the can by fitting it into a slit and leave the pin. Instead of a (complicated) bench vice system we have decided to create a cup. By making the top part of the mechanism removable the can will be able to slit in, thus fixing it in all directions.
After reviewing and redesigning we started on manufacturing the spray mechanism from aluminium.
Representation of the first spray mechanism design. Note that the empty space below the can is reserved for the piston.
This week we started to assemble the platform.the idea behind the design of the platform was to place everything on the platform, so the robot arm and the control box of the robot arm. We designed the platform with the height adjustable wheels. Because when the robot began to draw, the platform would be lowered to the ground to minimize the vibrations caused from the robot arm and to maximize the stability. After some handwork we finally managed to assemble the platform, the next step was to test if the platform would turn 180 degrees, and there was our first problem. The problem was while turning the platform, there was not enough space between the platform and the wheels, so that resulted in, that the wheels collided with the platform, so the wheels couldn’t make a 360 degrees turn.
We wanted to keep it simple, so our solution was to add two horizontal beams to the front of the platform and assemble the two front wheels on the ’new beams’, in this way we were able to extend the distance between the platform and the wheels to avoid a collision.
After a lot of research we narrowed our positioning technique down to a technology called SLAM (simultaneous location and mapping). Criteria for choosing were mainly cost and accuracy. Cheap systems that use magnetic fields or triangulation over sound/electronic waves are as of yet relatively inaccurate (10-20 cm on a 10×10 m field). The SLAM method uses only a stereo camera yet can achieve an accuracy of approximately 3 cm regardless of the area. This is done by tracking high contrast points in the image. By tracking their translation the camera knows how (relative to a high number of points) it is moving through space.
Currently we are working on using this opens source technology on a KINECT Camera and translating the coordinates that we get from the software to the system driving the robotic arm. We hope that by correctly implementing this we can know the position and orientation of the Robots base at all times with an accuracy below a 10 cm error margin.
For some (quite advanced) demo’s check out these video’s:
car driving while tracking its position
mapping your garden
Hey guys so here is a quick summary of the meeting of 29-09 including target points for the next meeting.
For those who are not yet familiar with the project, the goal is to paint on a large scale with a robotic arm.
The main challenge lies in the accuracy and determining the position of the robot to properly continue the painting after being moved.
In the meeting we made a list of all the involved problems and then subdivided them into three categories
- Accuracy and precision of the painted line. Possibly solvable by implementing a new nozzle or using painting masks.
Also an optimum for painting distance and speed has to be formulated for the best result.
- Position tracking. The challenge here is to find a way to accurately determine the position of the robot in relation to the drawing.
Mechanical motion and local visual confirmation might result in cumulative error, we will therefore focus on “global” visual confirmation and wireless position triangulation.
- Construction and interaction. We are aiming for a construction operate able by two people.
Also it has to be able to stabilize itself (or be highly stable from itself) in order to accurately operate the arm
During the upcoming week we will be researching these categories and discuss possible solutions as well as possible test setups.
Next week Thursday we will have another meeting and also update on the progress of the project