Development

This is the robotic arm with a modified 'forearm'. This allows the arm to cover a greater workspace, it is now possible for a straight line to be drawn between each point.

Development

This is a modified workspace for an arm with a shorter second link. A diagram of the pentagtram is superimposed to demonstrate that it can be followed by the arm.

Testing

Here is a trial run of our initial LabVIEW program with the motors at 15% of their maximum power. As can be seen, an acceleration profile will be required at a higher motor percentage because the inertia of the arm would become too great. This would result in the motors over- or under-counting. Especially when carrying a 1kg mass.

Testing

This is our initial run with a simple version of the LabVIEW program installed in the cRio. So far the program is designed just so that the end point of the arm reaches all five points on a pentagon, when it is finished it will follow the shape of a pentagram. At this stage we still need to write an acceleration profile so that the motors can be powered up to a higher speed.

Flowchart

This is a simple flow chart which was used to aid building of the LabVIEW program.

Programming

Working hard on the LabVIEW program.

Calculations

These are the angles we calculated for both joints of the arm to enable the end point to achieve all five positions on the pentagram. The expressions for beta and alpha determine the total angle which must be completed by each link for each step.

2D Kinematics

We have created a 2D plot showing the area which can be covered by the point at the end of the arm. This needs to be taken into consideration when writing the program. It would not be possible for the LED to pass through the white area of the plot.

Building Process

Here are a few pictures showing the building process and finished product.

Accurate marking out to ensure parts assemble properly.

This picture shows the assembly stage of the building process.

Here is the completed assembly excluding the cRio.

 

Elbow detail.

Detail of the shoulder joint and motor arrangement.

Final assembly compared to the solid works drawing.

CompactRIO

For the programming aspect of the project, we are using the CompactRIO (cRIO) from National Instruments (NI). It's an embedded control system which can be easily configured by the user. It is programmed using NI 'LabVIEW' software which allows programming to be intuitive and easily adaptable. For more information on the CompactRio follow this link http://www.ni.com/compactrio/whatis/. We will upload screen prints of our program (when we have developed it further) and images of the cRIO controlling our arm. In the meantime here is an example of how the cRIO can be used http://www.youtube.com/watch?v=_x5IziyOcAg.

Shoulder Detail

This image shows in detail the ‘shoulder’ joint i.e. The attachment of the arm to stationary base. The sections of box section are sufficiently far apart in the vertical direction to spread the load of the 1kg mass on the axle. A total of six flange bearings are fitted to the axle to minimise the torque which has to be overcome by the motor which is connected to the axle with a flexible coupling. Flange discs allow the rotation of the axle to result in movement of the arm.

Elbow Detail

Above is a SolidWorks drawing of the elbow joint. The timing pulley (top) is connected by a belt from the motor. The thin blue lines which can be seen are circular discs which attach to the axle and 'forearm' of the robot allowing it to rotate with respect to the timing pulley. An optical encoder (bottom) is connected to the axle with a 'flexible coupling' (for practical purposes). This feeds information back to the program via a cable enabling it to correct any discrepancies effecting the angle through which the 'forearm' turns e.g. slippage between timing belt and pulley.

Design Developement

As can be seen from the solidworks drawing we have decided to make alterations to our chosen design.

We changed the structure of the arm so it is now constructed from four sections of box section instead of two. This is because the arm must carry a minimum of a 1kg load and it needs to be able to withstand the forces applied.

Initially we placed the motor for the elbow joint on the opposite side of the shoulder pivot to act as a counter-weight. We decided that the 0.1kg mass of the motor was negligible compared to the 1kg applied load. It is also important that the moment of inertia is as close to the shoulder pivot as possible to maximise it's speed and agility. Taking this into consideration we moved the motor on the other side of the pivot and closer to the elbow joint. This simplified the design and reduced the size of the belt, minimising the chance of it inducing errors into the system.

3D Modelling

Here is an image of the completed design made on SolidWorks, our next job is 2D drafting to produce drawings which can be taken into the lab.

Detailed Drawings

These show detailed diagrams of ideas for the motor configuration and elbow joint.

Initial Design

This is the final design we developed from our initial ideas.

Initial Ideas

These are our initial ideas for the design of the arm. Each design incorporates a combination of rotating and sliding joints. We chose to develop the sketch at the bottom centre. It is simple and this reduces the chance of potential errors being induced into the system.

What are we doing?

We are designing and building a programmable mechatronic arm with two degrees of freedom. It is required to pass as quickly and accurately as possible through six points in a two dimensional plane. This will be detected with light sensitive diodes from an LED mounted on the arm. The arm must carry a 1kg load and a wii remote to measure acceleration and deceleration, at a point on the end of the arm.

Why are we doing it?

We are investigating an idea for a competition which will be taken by second year students on the Medical Engineering course. The project will link the second year design and manufacture module to current university research in physiotherapeutic robotics. Our robot, if successful, will be used as a teaching aid for students.