Prototype 0 - Results
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This prototype was entirely 3D printed with the sole purpose of testing the adaptability of the gripper design. Videos of the gripper operating are shown below.
Goals Achieved
- Successful testing of an adaptive gripper design
- Prototyping methodology productive use of time
- Cost nothing to fabricate and test
The goal of this prototype was to see if the adaptive gripper mechanism would work. In this respect it was able to successfully prove the adaptive gripper design works. This prototype also cost very little in terms of raw materials, time and assembly time. This proved to be an efficient use of time.
Other Successes
- adjustable tip pitch
This was not a design intent, but a welcome result. the pitch of the tip can be controlled by adding shims in the extendable link jammer. This effectively increases the length of the outer link which pitches the tips inwards. This can help reduce the affect of loose pin joints in the links.
Improvements
- Tighter pin joints
- Greater consideration for gripper material
- Extension rod should be supported front and back
- Careful consideration for adaptive gripper spring tension
- Attack angle
One thing that was overlooked was the importance of close fitting pin joints. During assembly several pin joints sheared off due to design overlooks, this lead to an exaggerated running fit in the left side gripper joint. This meant that the rotation points in the link were shorter than intended, resulting in undesirable claw movement. one such movement was jamming in the close configuration, as well as an outwards pitch.
For this prototype it was not as important to include grippy material at the grippers. During testing it was found it was impossible to pick up any items without some sort of compliance. This shows the importance of proper grip material selection and testing in future prototypes.
During testing it was noted that the piston rod driving the assembly experienced quite a bit of side to side movement. This was not a requirement in the prototype, but it does show that these forces are present and should not be neglected during final design. The final design should include mounting and the front and back of the lead screw, should a lead screw be used.
During testing, the rubber bands controlling the adaptive behavior was changed quite often. It was either too loose for the object or too tight. In the final design more calculation should be performed for the selection of the spring, or ensure the design allows for the tension element to be easily swapped out for elements of different stiffness to ensure the ideal configuration is utilized.
The attack angle being described here, is the angle between the ground surface and the plane of the claw. the way in which the tips are designed, it is best to pick up the items at an attack angle of 90° or 0°. 0° is an impossible angle as it would mean the bottom of the claw would have to scrape against the ground during item interaction. If 90° is good enough for the robotic arm, then no further consideration need be made. If this is not the case, it might be worth considering cutting a chamfer on the bottom side of the claw tips to allow for the gripper to gasp items at a 45° angle, which may be more convenient.
Further Questions
- Allen key attachment
- Test different types of gripping material
- Required size
The Allen key attachment is still not figured out and needs to be determined ASAP so that a more concrete prototype can be developed. Several concepts are floating around but none have been decided upon due to various disadvantages.
The gripping material may make or brake this design. This is arguably the most important property of the design. This should be a main focus in future prototypes, it may be worth buying several types of rubbers/polyurethanes from McMaster to test out the different thicknesses and hardness's if budget allows.
The overal size of this gripper seems to be suitable, but of course, smaller means lighter and less torque required at the cost of smaller jaws. The current size seems to work well. Sizing should be reconsidered for future, future prototypes way down the line.
Steps Moving Forwards
- Allen key attachment
- Gripper material
- Next prototype
- Drive mechanism
- Motor selection
- FEA simulation
- Other optimizations
- Rigorous torque/speed calculations
- pressing buttons?
- force sensing?
The drive mechanism currently being considered is a lead screw. This seems to be the best option but others may be considered.
To press button, may want to use the screw driver mechanism - spring back to prevent going through the keyboard.
A metal prototype, with proper actuation seems to be the next obvious step forward in this design cycle for the gripper. Something else to consider is the available budget. This project is relatively small compared to other projects such as drivetrain or arm - these projects will need a much larger budget. It might be considered to dive into a final design to save on costs, with the exception of the motor. The motor can be swapped along with a bracket once motor power requirements are verified. This way if things work only a few parts will need to be swapped out.