Team 17 - 2) Design Process

    The objective of this machine is for a user to place a coffee cup and milk pitcher in the system and then press a button to draw a latte heart. To achieve this goal, we utilized a six-bar rectilinear type mechanism that included two grounded joints and multiple complex link shapes.

    By using the Planar Mechanism Kinematic Simulation (PMKS) website, we were able to experiment with different configurations of this six-bar mechanism which resulted in the following design:

Figure 1. Full assembly of the latte art robot

    The dimensions of this design are a 1:1 ratio to the PMKS simulation due to the lengths being ideal for the size of both the pitcher and coffee cup.

    There were many major design decisions that occurred throughout this project, one being the horizontal mounting of the ground links:

Figure 2. Image of the ground links

    To minimize interference with the focused trajectory in the mechanism, this placement of the links was ideal. This allowed for the pitcher to have more room for movement and also allowed for the coffee cup to be placed on the ground without being obstructed by vertical bars.

    The next major design decision was the placement of the pitcher. We decided on having it in the middle of the system which called for the parallelism of the outermost links (Figure 3). Due to this decision, an adjustable mount was created for the pitcher which worked nicely for pouring milk.

Figure 3. Image of the parallel outermost links

    A challenge we faced with this design was how much weight was being placed on the input link. To solve this problem, we went through multiple iterations of the outermost links:

                                                                                                                                                                      Figure 4. Iterations of the outermost links

    As you can see in Figure 4, with each iteration we gradually removed more and more from this link. The final form continued to have its original functionality which greatly improved the weight issue.

    Along with reducing the weight, more support needed to be placed in the system. We decided to put multiple ground links in parallel or close to each other to counter the load on the ends of them.

Figure 5. Parallel ground links

    Another design point that went through some iterations was the kind of motor we were going to use. At first, we believed that a stepper motor would be able to drive the system. But as we learned more about exactly how much load was being placed on the mechanism, we decided to use a DC motor. A belt and pulley system was used to reach the length of the input link due to the decision to place the motor on the back plate of the system.

Figure 6. Image of the motor

    The final major design decision was the inclusion of springs. These springs were placed on the top hangover bars that were recycled from an earlier iteration of ground links. Again, due to the load being applied to the system, these springs greatly helped the motor lift the pitcher when it is in its vertical trajectory phase.

Figure 7. Hangover bars with springs

    Finally, to reduce the amount of play on the system, we went through multiple iterations of shaft lengths. At first, we chose random lengths that worked with the pitcher dimensions, but as we continued the project, we learned that we needed to shorten these shafts and make the mechanism tighter. By including spacers and shaft collars, we were able to reduce as much play as possible.