P10010: Motion Tracking Sensor

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.

List of Metrics
Metric No. Metric Units Importance
1 Final Accuracy Degrees
2 Dimensions in
3 Life Between Recharging Hours
4 Strength of Enclosure Forces Sustainable
5 Measurement Capability Degrees of Freedom
6 Locations Sustainable Arm, Leg, Back...
7 Points of Contact 1, 2, 3,..
8 Data Storage Capability GB
9 Efficiency Time to transmit data
10 Wired/Wireless Yes/No
11 Sampling Rate Hz
12 Weight lb

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 Final Accuracy Dimensions Life Between Recharging Strength of Enclosure Measurement Capability Locations Sustainable Points of Contact Data Storage Capability Efficiency Wired/Wireless Sampling Rate Weight
Sanitary x x
Portability x x x x x x
Comfort x x x x x x
Durability x x x x
Accuracy x x x x x
Ease of Use x x x x x x

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.

Polhemus Patriot
Wireless Motion System- allows up to 4 markers with 6 DOF each. Rechargable lithium battery assembly takes 2 hours to charge. 50 Hz per marker, interface via either RS-232 or USB. However- system is magnetic- would not be acceptable for our project. This is the system Sara talked about when she referred us to a local golf pro.
Polhemus Patriot Brochure
Comparison of Polhemus Systems


AccuPath Industrial Lumbar Motion Monitor
Big, bulky backpack-looking contraption that simulates exoskeleton of spine. has a 100 foot range from receiver and 4 MHZ sampling rate. When packaged in a suitcase entire system weighs 44 lbs. Not practical, but one of the only accurate lumbar-focused trackers on the market.
AccuPath Industrial Lumbar Motion Monitor


Vicon Motion Capture System (Sara)
Control- This is the video camera system Sara uses at Nazareth.
X-Sens Inertial Motion Capture Suit
Full body tracking with 14 6 DOF sensors. Completely wireless, up to 500 foot range from reciever. Suit takes 10 minutes to setup and can be worn under regular clothing. Bluetooth communication, USB interface. Weighs 4.2 lbs, operating time approximately 3 hours. Accuracy approximately .5 degrees. Looks very expensive?


X-Sens Suit

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 Polhemus Patriot AccuPath X-Sens Vicon (Control)
1 Need 2,7 Sanitary 4 Time? ~5 min 0 seconds Impractical N/A
2 Need 1,2,3,4,7,12 Portability 1 lb, in 2 ounces per sensor, 2.9x.865x1.25'' ~3 lbs, 5x23x3'' 4.2 lbs, Full Body Suit Not Portable
3 Need 1,2,5,7,12 Comfort 2 1-10 4? 4? 6? 10
4 Need 1,2,3,4, Durability 3 Newtons ? ? ? N/A
5 Need 1,5,8,9,11 Accuracy 2 Degrees, Sampling Rate .003, 50 Hz ?, 4 MHz .5, up to 120 Hz 1, 100 fps
6 Need 2,3,6,7,9,10 Ease of Use 1 Seconds ? ? 10 minutes 30 min setup

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.

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

General Specification Spreadsheet

Sensor Specification Spreadsheet