Blowing up Fingers! Take 2

After all the simulations and drawings it was time to print and test. This is the design which we have previously tested in CATIA. The bending motion is even better than expected, thus the model can be considered a success. Nonetheless we discovered that the material is very weak and the finger already broke apart. The next model will be reinforced at, what we discovered to be, critical points.

finger working under air pressure

Video take of an applied pressure test to the first finger model


Exploration With Different Valve Connections

An important part of a pneumatic system are valves. These were examined to test which is the most air-tight. Depending on the manner of connection (tapping or screwing) a softer or harder material should be chosen. Further, printing circular forms perpendicular to the printing direction, will cause oval-like shapes in soft and flexible materials due to the weight on top of the print. This phenomenon could be observed in a prototype of a John-Guest connection.

Below you can see the cross-sections of the different connections, from top to bottom post threaded connection (used in the one-way valves and gripper), pre threaded connection and a John Guest connection.

Post-Tapped Thread Connection

Pre-Tapped Thread Connection

John Guest Connection


Printing One-Way Valves

We explored if it is possible to print one-way valves. Two prototypes were printed and both works surprisingly well. Although some air is still leaking out (because of the cleaning process to remove support material as it damaged the enclosed parts), it demonstrates that functional parts can be printed quite easily.

Below you can see the cross-section of both valve designs. The blue parts are the enclosed and can move around. The reds parts are seals made from softer material so the moving part can fully close one direction if pressure is applied from one side.

Ball One-Way Val

One-way valve based on a free-moving ball in an enclosed space. The ball is not able to close the upper output due to the form of the enclosed space, however it is possible for the ball to close the bottom output because of the sealer.


Plug One-Way Valve

One-way valve based on a plug-like object. The plug can make an up an down movement to change the state of the valve. The top part is completely solid (and can therefore close the valve), while the bottom one has air inlets.



Initial Model Gripper-Finger

Today, the first model of a gripper-finger was made in Rhinoceros and sent to the Objet500 Connex printer (1). The model is visible in the figure below. This printed model is used to test the initial behavior of the material and air chambers.

The model of the gripper-finger was printed later that day. However, while removing the support material one bellow broke immediately, making it already unable to function. Thereby we had issues to completely remove the support material on the inside of the finger in the air-chambers.

Therefore the following was concluded from this first prototype:

  • The thickness of the finger is to small. It broke too quickly. So for the next model a thickness of 2 mm will be applied (instead of 1mm).
  • Also the finger was to flexible. It could not stand straight on its own. For a next prototype we will have to make the material less flexible. That means the material for the next prototype will be a combination of 70% ridged and 30% soft material, instead of 60%/40%.
  • Lastly, we need to think of a way to successfully remove the support material inside the finger. First ideas are to add a ridged cylinder in the whole length of the finger which can be pulled out after printing. This will ensure that there is space to erode support material. Secondly, a one way valve at the top of the finger could be added, so water can flow through the whole finger and clean all the air chambers, but prevent the air from leaking when in use.

For the next prototype these findings will be used to improve the gripper-finger.


Rhino model of the printed finger.

IMG_20151012_111017IMG_20151012_111035 IMG_20151012_111025IMG_20151012_111041

The print from the Rhino model. Although it looked good on first sight, there it is more difficult to make a working finger than we thought. For example one bellow broke immediately when it was cleaned (broken bellow is shown in the last two pictures).

(1) Stratasys,

Connex 3D Printing

Today we did a test with the Objet500 Connex 3D printer to see how the printing process works and what the effect is of using rigid and flexible materials.

We printed three specimen (rigid, flexible and a composite) to use it for a tensile strength test next week. The pictures below show the results.
The most interesting print was the composite as with the structure inside it you can easily twist the specimen, but its inside structure prevents bending. This is done by making rigid cylinders (cores) over the length of the print and bind them together with more flexible material. The cylinders gives the composite the property to resist bending (as it is rigid over the length) while the flexible material can make the cylinders move dependent from each other and therefore twist.

IMG_20151001_123346Our specimen prints are processed by the connex printer

IMG_20151001_170518The printing result. The pink material is support material which needs to be cleaned with a water jet ot by scratching it off. The total printing time was 30 minutes.


This picture shows how the composite specimen can easily be twisted due to the combinations of rigid and flexible materials. Bending it is quite impossible though.