Concept Selection
CONCEPT SELECTION:
Four different designs were sketched based on the combination tables created. Design I is labeled as the “Double Chuck Slide Concept.” Design I utilizes four motion devices to perform the required function. A rotary motion device would be used to drive the gripping mechanism of the container base. A second rotary motion device would drive the gripping mechanism for the closure. A rotary motor powered linear actuator is utilized in the design to move the top mechanism to the closure. A rotary motor would be employed to spin the closure off the container. The advantage of this design is that it applies a motion device for every action required. For development purposes, the team believed that it would be advantageous to incorporate a modular design. The advantage of a modular design would be that it applies a motion device for every action; this allows independent development and optimization of subsystems. A disadvantage is that modular designs are more expensive and prone to failure to the higher amount of components.
Design II is labeled as the “Single Chuck Cam Concept” and is similar to Design I since it uses four motion devices, three of which perform the same function as in Design I. The difference between Design I and II is that Design II utilizes a spring to provide the downward force onto the closure. The downward force is controlled by a cam that is driven by a rotary motor. When the cam is rotated downward, it allows the spring to push down the top mechanism to the closure of the container. When the cam rotates upward, the top mechanism is brought back to the home position. The advantage of this design is similar to that of Design I; it is a modular design. An advantage of this design over Design I is the rotary motor that would drive the cams are more cost efficient than the rotary motor powered linear actuator. However, the modular design is more expensive and prone to failure. Furthermore, the required force and distance to travel by the top mechanism would be difficult to fulfill with a spring.
Design III is identified as the “Sponge Grip Concept.” The design uses three motion devices. A rotary motor would drive the gripping mechanism to grasp the container base. A rotary motor powered linear actuator would lower the top mechanism to the closure. The final motion device would be a rotary motor, which would spin the closure off the container. The closure would be gripped by a friction type pad, which would eliminate the need for a mechanical gripper and a motion device to drive the gripper. The advantage of this design is the reduction in amount of motion devices. Keeping the amount of motion devices to a minimum reduces cost. Since only three types of motion are required as opposed to four, the design becomes less complex. A downside is the friction pad can wear out over time and require replacement.
Design IV is titled the “Rotating Wheel Concept.” The design uses two motion devices. A rotary motor drives conical wheels (which be made of a rubber type material to provide friction) that are used to spin the closure off the container. The container and closure is brought to the friction conical wheels by a linear motor. Springs are used to provide the force for the grippers that hold the container base. This would require the end-user to move the grippers out to place the container in the machine. This is a disadvantage because the team would like the grippers driven and move automatically into place. Another disadvantage is that the rubber type material of the conical wheels would wear over time and require replacement. However, the machine does have the advantage of the least number of motion devices. As a result, Design IV is the simplest design and theoretically costs the least.
Using the customer needs and a survey that was distributed to people within in the selected demographic; the most important needs were determined. A concept-screening table was generated to narrow the designs to a preliminary concept that would be pursued. The most important needs were determined to be ease of operation, versatility, safety, ergonomics, durability, and low cost. The team also felt that ease of development was important since a complex design would pose the danger of a failure to complete the project. Based on these selection criterions, the designs were rated with Design I being the baseline. The designs were rated as being either par, better or worse than the baseline. The ranking helped determine that Design I should be continued, Design IV should be eliminated, and Designs II and III should be combined since they were very close in net score.
Designs II and III were combined to create Design V, the “Single Chuck Sponge Grip Concept.” A concept-scoring table was generated to rate Design I and the combined design. Furthermore, in the concept-scoring table, weight was given the selection criteria based on which criteria the group felt was more important. The designs were ranked and according to the results, the team chose to purse the combined design.
