14.2 Project Analysis & Prototype

Kinematic Analysis:

• plots/description of ideal motion/force profiles for problem statement

  • Here are the following problem statement constraints:

    • The movement simulation of a real articulated finger.- The initial movement was achieved in “Figure 1” and has been improving until getting our final desired movement showed in “Video 2”

    • Optimum trajectory path that will determine the dimensions of the moving linkages.- After selecting the path, all the links dimensions were taken from MotionGen and modeled in Solidworks as showed in Figure 4 and 5

    • Constant velocity output to generate a continuous natural movement.- The constant velocity motion was achieved since the second iteration of the mechanism presented in 'Figure 2' where two actuators were added

    • The three fingers will have to be actuated only using 1 DOF (The action of one motor).- The prof of concept of one DOF is presented in 'Video 5' where our mechanism only required the movement of one actuator of the upper gear

    • The tip of the fingers will need enough friction to archive moment in a normal flat surface.- Will be implemented with high friction material (Like rubber) at the end of the finger in next prototype

    • Weight distribution and space management of the mechanical and electrical component will be key factor to consider.- Showed in “Video 5” space optimization has being considering since prototype three

For designing the finger mechanism, our first drawings were focused on accomplishing a descending movement trajectory with 1 DOF.

1. The main problem with achieving 1DOF in this iteration was the velocity profile at the tip of the finger. There was a long pause just in the middle of the movement. (See Figure 1)

2. For the next iteration, a second actuator was implemented, achieving a smoother motion. The system maintains 1 DOF if the two actuators have the same angular velocity and radius. (Figure 2)

Open Figure 1- First Iteration

Open Figure 2 -Second Iteration

The next iterations were focused on achieving the same path movement with a more humanoid finger shape of the mechanism, utilizing typical hand bone structure as a reference for size proportions. (Figure 3)

3. Explored a more horizontal motion, conserving an equal ratio of the angular actuators moving in opposite directions.

4. Conserved equal ratio of the angular actuators and direction.

5. Did not conserve equal ratio of the angular actuators but conserved direction. This gives more room for dimensional errors before hitting an undetermined position.

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Figure3 - Iteration testing different inputs movements

Finally, we chose the configuration where the two inputs links rotate in opposite direction which will help us implement 2 gears in its construction. The part section is presented in Figure 4:

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Figure 4 - Chosen Configuration from MotionGen

Solidworks model:

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Figure 5 - First 3D model using Solidworks - Model of finger mechanism

• Mobility calculation of all systems/subsystems

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• Kinematic analysis

For the desired model we made the analysis in Solidworks having the velocity magnitude at the tip of the finger. (Video 1)

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Video 1 - Chosen alignment of the gears

In our model, we noted the position of the gear configuration and how it showed different end paths.

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Video 2 - Misalignment of the gear by one tooth counterclockwise

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Video 3 - Misalignment of the gears two teeth clockwise

For this, we implement the following gear design:

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Figure 6 - Gear design with teeth alignment indicator

• We wrote a MATLAB code that allows us to calculate the torque. This part will allow us to easily recalculate and select the motor if any variable, such as the weight of the center of mass, changes in future iterations.

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In addition, we conducted positional analysis of the two five bars represented in our hand-finger system.

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Hand Mechanism - Measured Link and Angle Values

The two five-bar mechanism positions and paths were modeled with the first geared five-bar system consisting of links 1 through 5 and the second five-bar system representing links 5-9.

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First Geared Five-bar Mechanism

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Second Five-bar Mechanism

Physical Prototype:

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Figure 7 - 3D model and physical prototype

Iteration Documentation:

Iteration 0:

• Iteration 0 consisted of our MotionGen models and designs. These helped us determine the most optimal orientation and dimensions of our parts. From this we were able to choose the most optimal model for us to make in the next iteration.

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Figure 8 - Iteration '0'

Iteration 1.0 (6mm wooden linkages)

• Next, we cut, printed and assembled our first physical iteration of our hand design. The links on the tip of the finger were loose due to a manufacturing issue, causing out-of-plane movement outside of an acceptable range. Additionally, in this design we used 6mm wooden linkages but these proved to be too thick for the prototype to move and be assembled efficiently. These issues we desired to fix in our next iteration. Iteration 1.0 was beneficial to us in proving that the design of our finger mechanism movements worked outside of our CAD designs.

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Figure 9 - Iteration 1.0

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Video 4 - Motion of prototype 1.0

Iteration 2.0 (Gears)

• From previous research, we designed gears that were connected with a shaft. While this design seemed promising, our gears broke due to the tension of the hold.

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Figure 10 - Gear model Inspiration

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Figure 11 - First gear iteration broken

• Then we prepared two improved versions with space between the gear and the base. However, this required us to print it vertically. We also tested a design separating the gear into two pieces.

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Figure 12 - Second Iteration of gears

• Finally, the best design after the prototyping was the 2-pieces gear as it printed best and was most effective at providing the necessary space between the gear and base.

Iteration 3.0 (Acrylic with three finger mechanism)

• Learning from our design issues in iteration 1.0, we decide to get rid of the the final loop on the finger tip and extended the length of the ternary link in the middle. This reduced our number of linkages making our design more streamlined and effective.

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Figure 13 - Left.- MotionGen of Iteration 1.0 path; Right.- MotionGen of improved Iteration 3.0 path

• Then, we engineered a new design of the fingers while improving the design of the knuckles mechanism.

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Figure 14 - Finger link design

• Next, we put them together in a V3 prototype:

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Video 5 - Mechanism movement and prof of concepts

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Figure 15 - Iteration 3.0 Prototype

Iteration 4.0 (laser cut based with optimized holes)

• For the next iteration, we improved our system by laser cutting test holes in acrylic in order to design our acrylic hand bases with holes for optimized fit. Additionally, we designed the pinkie and thumb bases that once printed will serve as stabilization for the hand system. Currently designed to be just PLA but we are considering the addition of a roller ball in the pinkie and thumb finger tips to allow smooth system movement.

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Figure 16 - Iteration 4.0 Prototype

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Video 6 - Iteration 4.0 3D Modeling

Draft BOM:

Next Steps:

• Deep motion analysis of the mechanism in MATLAB 

• Detailed design of the finger

  • 3D links 

  • Double link

• Dimension the motor

• Defining and purchase commercial elements ; Motor, pins, belt, electronics

• Redesign the palm using surface tools

• weight balance analysis

• Fin

• Design for the static fingers with balls and able to move with step motor

Links

• Previous ----- Project Proposal

• Next ---------- Implementation