REQUIREMENTS
After meeting with the client David Calley, team 4 has come up with eight different needs/ requirements that must be present in the pneumatic stapler. As mentioned by David these eight requirements are a must for the stapler to be a functioning part of Elemental Motors’ manufacturing machine. These requirements are based on several components and are present in similar systems that make up the motor manufacturing machine. Found below are the customer requirements that were given by the client for the pneumatic stapler. While configuring the client requirements the team also decided on seven engineering requirements listed below that will be used as a guide for the development of the stapler.
Customer Requirements (CRs)
The customer requirements are based entirely on what the client needs within the system. They are used as the outline for building the final project design. Using the customer requirements, the team stays within the parameters while designing the stapler. Each one of the requirements is given a weight or ranking to determine the importance of that particular requirement. These weights are from 1 to 5 with 1 being the lowest priority and 5 being the highest priority. The importance of these weights keeps the team on track and focused on the most important topics. Listed below are the customer requirements with the weights and description present for a better understanding.
1.High Speed : This stapler is responsible for placing 160 total pieces into a magnet ring that has a diameter of 115 mm. While the stapler is functioning, it needs to place all 160 pieces within a total time of 3 minutes. This time of 3 minutes is based on similar systems that complete their tasks in the same amount of time
2.High Efficiency : The efficiency of the stapler comes down to how well its functions without experiencing an error in the operation. As stated by the client, this stapler needs to function 100% with no errors experienced.
3.Functioning prototype : Another critical component of the stapler development is producing a functioning prototype. For the prototyping of the stapler, it will need to be fully modeled on CAD by the first week of July. Having it modeled on CAD the prototype can be either 3D printed or machined to test its functionality during the month of July and August.
4.Size : Based on its weight and the client needs, the size constraints of (254mm^2) for the stapler is not critically important. It is helpful to stay withing this size constraints but not absolutely necessary for a functioning stapler.
5.Cost Effective : To design a feasible stapler for Elemental Motors it will need to be relatively cost effective. The total cost to develop this stapler needs to stay within the allowed budget while providing a functioning and reliable machine.
6.Fully Automated : Apart from loading the machine with the 160 total components it needs to function fully automated. After being loaded the stapler needs to place the pieces without any human interaction until the magnet ring is fully assembled.
7.Long-Lasting : The stapler needs to function for months on end without being replaced, taken apart, or maintained. It needs to contain high quality machined components and parts to avoid the stapler failing.
8.High Torque : To support the torques applied on the turn table the motor needs to supply a high torque. The high torque needs to be able to lock the turn table into position and keep it from moving when magnets are placed.
Engineering Requirements (ERs)
From the client meetings the team was able to set up the customer requirements. And then the team used those customers' requirements to decide on the engineering requirements. The engineering requirements are used to showcase how the client's needs will be met. Using both a measurable scale and tolerances the team will be able to satisfy the client. Setting these ER’s, the team can quickly reference what is needed while being able to easily communicate the ERs to David. Listed below are each one of the engineering requirements along with their targets, tolerances and justifications.
Decrease cost: The direct drive motor is produced in-house, costing the company roughly $150 to produce compared to around $300 for high-quality gear boxes. For all designs, 12” of 1” stainless steel round is $379.65 compared to $8.09 for aluminum, so all parts will be made of aluminum outside of those susceptible to fatigue. Ideally decreasing the cost by about $500 with a tolerance of ±$50.
Improve Efficiency: Fewer moving parts leads to increased accuracy and makes the target of 0 misplaced parts much more possible. While using a direct drive system 100,000 steps per revolution can be achieved by switching from a 17-to-21-bit encoder. This resolution will provide precise positioning allowing for 0 errors. Increasing the resolution from 40,000:1 to 100,000:1 with a zero tolerance.
Improve Quality: Fewer moving parts leads to less fatigue wear, regardless of design. Expected stresses on our design maxes out well below 130 MPa and should allow us far greater than 1⋅10^7 cycles of operation for even the aluminum elements. Expected life cycles of 1⋅10^7 with a tolerance of ±1⋅10^2.
Stronger Motor Specs: The direct drive system gives us 50 Nm of torque, while most servo/ stepper motors are around 3-4 Nm without an expensive gear box. Switching to direct drive we can achieve more torque from the in-house G3 114 motor with a much high precision. Achieving a torque of 50 Nm with a tolerance of ±10 Nm.
Improve Programmability: Similar to efficiency, fewer parts lead to fewer lines of code required to control the system. Additionally, the direct drive system enables the use of a 21-bit encoder, allowing for greater control compared to the 17-bit encoder used by the alternative drive systems. Using a 21-bit encoder with zero tolerance within the programming.
Size Constraints: The build space is set by the client based on the total size of the motor manufacturing machine. Each subsystem was given a size constraint of 254mm^2 for all systems to fit. There are no height restrictions given as long as the system functions. Without a belt or gearing system, this design can easily fit in the 254mm^2 space. Required size of 254mm^2with a tolerance of ±2mm^2.
Improve Machining: Currently the estimated machining time is calculated at 80 hours costing $1.50 per minute of machining. With the reduction of parts and part complexity the machining price will decrease from $1.50 to roughly $1.00, along with decreasing the total machining time. The desired machine costs $1.00 with a ±$0.25 tolerance.
House of Quality (aka QFD)
The House of Quality, which is also known as the QFD has been a critical aspect of the stapler design. Setting up this QFD allows the team to build a relationship between both the engineering requirements and the customer needs. This relationship is important when deciding what area to focus on during the design. Along with the design process the QFD is a great tool that the team can use to present the design process with critical information to the client. From there the client can approve the priorities are correct along with helping the team brainstorm additional ideas to achieve each requirement. As the team moves forward with the development of the stapler the QFD plays an important role in keeping the team on track and focused. Since it outlines the needs of both the client and the team it is useful to references when making sure that each task is done to the specifications of the client. These specifications need to be met in order for the client to be pleased with the process and eventually the overall design on the staple.