P08023: Air Muscle Artificial Limb I

Establish Target Specifications

Table of Contents

Step 1. Prepare the List of Metrics

The table below presents the metrics, or engineering specifications, that will be used by the team to design against.

QFD Chart

List of Metrics
Metric No. Metric Importance Units
1 DOF - Finger 1 m
2 DOF - Thumb 1 NA
3 DOF - Pinky 1 Newtons
4 Number Joints 1 Newtons
5 Number Tendons 1 NA
6 Number Muscles 5 NA
7 FS 3 NA
8 Life Cycle
9 Force Supplied
10 Displacement
11 Working Pressure
12 Feedback Loop
13 Assembly
14 Manufacturing
15 Engineering
16 Materials
17 Equipment
18 Muscle Length
19 Length/Force Ratio

The metrics, or engineering specifications, that you created in the preceding list should be directly related to the customer needs. In other words, if you have created an engineering specification, it should have some relationship to a need imposed by the customer or the marketplace. Use the table below to map your customer needs against the metrics (or engineering specifications). In many design and product development circles, the rows along the left is often referred to as the voice of the customer, while the columns across the top are often referred to as the voice of the engineer.

Customer Needs as Related to Engineering Metrics Matrix
Needs and Metrics Engineering Metric 1 Engineering Metric 2 Engineering Metric 3 Metric 4 Metric 5 Metric 6 Metric 7
Development and Implementation of Air Muscles x x x x
Implement Control Mechanisms and Algorithms for Muscle Control x
Designing a new Robotic Hand x x x
Low Cost Hand x x x
Scalable Product x x x
Interfacing Issues

Step 2. Collect Competitive Benchmarking Information

Relatively few Sr. design projects start from a clean sheet of paper. In most cases, there are some baseline solutions or products that could meet the vast majority of the customer's needs.

Write one or two paragraphs about each benchmark solution from the market place. Include a picture of the product, preferably illustrating the product in use or operation.

Air Muscles
Click on Air Muscle.

Click on Air Muscle.

The proposed work will utilize low cost air muscles (also known as McKibben Air Muscles) to generate forces in a robotic hand. Traditionally, more costly, methods for generating forces in a robotic hand are gears and levers, motors and servo controls, or hydraulic controls. Air muscles are simple to use, pneumatic actuators that have a high power to weight ratio of 400:1.

Air Muscle Link: http://www.imagesco.com/articles/airmuscle/AirMuscleDescription01.html

Solenoid Valves
Solenoid Valve Schematic.

Solenoid Valve Schematic.

The proposed work will utilize solenoid valves to control the fluid flow to the air muscles causing them to shorten and elongate in the same manner as natural muscles. A solenoid valve is an electromechanical valve for use with liquid or gas controlled by running or stopping an electrical current through a solenoid, which is a coil of wire, thus changing the state of the valve. The operation of a solenoid valve is similar to that of a light switch, but typically controls the flow of air or water, whereas a light switch typically controls the flow of electricity. Solenoid valves may have two or more ports: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports. Multiple solenoid valves can be placed together on a manifold. (Wikipedia Reference)

Solenoid Valve Links: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html http://en.wikipedia.org/wiki/Solenoid_valve

Benchmark 3
Describe the third benchmark solution here.

Use this table below to compare how pre-existing solutions should compare against the design team's efforts. See the example Table 5-6 on Page 80 of the text by Ulrich and Eppinger.

Competitive Benchmarking Matrix
Metric No. Need Nos. Metric Importance Units Benchmark 1 Value Benchmark 2 Value Benchmark 3 Value
1 Need 1 Optimal Muscle Length Extremely m or ft Air Muscle Design
2 Need 2 Control Mechanism and Algorithm for Muscle Control Extremely NA Solenoid Valve Configuration
3 Need 3 Design of New Robotic Hand Increasingly Important NA New Air Muscle Design Needed Solenoid Valve Configuration has to Be established
4 Need 4 Interfacing Issues Not a main Concern NA How Air Muscle Works, is it Sealed?
5 Need 5 Reason for Constructing Arm NA Air Muscle Provide Cheaper Methods
6 Need 6

Step 3. Set Ideal and Marginally Acceptable Target Values

Given the customer needs, awareness of the marketplace, and resource limitations of the current project, assign preliminary engineering specifications on each of the metrics. In addition to setting the nominal or target value or each specification, provide guidance to the team on the ideal value or direction that the team should strive for, once the nominal target values have been realized.


This will take place during the first week of SDI when the team is assembled and can agree on these target values.

List of Metrics
Metric No. Need Nos. Metric Importance Units Marginal value Ideal Value
1 Need 1,2
2 Need 2,4
3 Need 5
4 Need 6
5 Need 5,1
6 Need 6,2

Step 4. Reflect on the Results and the Process

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