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----- Original Message -----From: Truman Prevatt, PhDTo: Greg Roskies ; RideCampSent: Friday, April 13, 2001 8:18 AMSubject: RC: The Impression PadGreg,I've seen the impression pad and it does what it is designed to well - as I said before. However, I've spent the last 25 years developing systems (space and ground based) using sensors of all types and every sensor while good at the things is is designed for is not optimal for every possible application. I've been around the block several times with sensors, I don't really think I need to own one to understand how and why it works.
NASA has on orbit both the an optical and an X-ray telescope soon to put on orbit another satellite which is in the microwave region. Why, because nither in and of itself will give a complete picture. The radar detector bought in 1990 will not work against all police radar frequencies used today. On a pitch dark night someone can easily sneak up on you. But if you put on nigh vision goggles ( which are nothing more than an infrared camera ) you can see them as plain as if it were noon.
The technical reason is every physical, chemical and/or electrical material and component has something know as "bandwidth." It is a fundamental limitation below and above which the sensor will not respond - or more likely not response sufficiently. The eye's bandwidth is the visible portion of the radiation frequency spectrum. The human ear is about 50 Hz to 16,000 Hz.
I would suspect - having looked at the pad the bandwidth is somewhere around zero to maybe 1/4 of a Hz. From discussion I have had on portable bridges the frequency of a horse at a walk is about 2 to 4 Hz. That is when a horse walks this body is changing positions 2 to 4 times a second. Hence there is movement in his back, loins and shoulder at that rate. At a trot the frequency gets higher and even higher at a canter and gallop.
Materials such used in the Impression Pad tend to average the highs and low -attenuating the amplitude in the process. Hence the reading is averaged and the peak pressure is not recorded. If the frequency is too high, that is the pressure is changing too fast, the material dose not respond at all.
The active pressure pad sensors which I am familiar made by people such as VistaMed, Novel (http://www.diashoe.com/), Tekscan (http://www.tekscan.com) are designed to faithfully record values of pressure at frequencies from zero (static) up to 10 to 100 Hz depending on the amount of money you want to spend by sampling the sensors in the pads at fairly high rates and down loading them to a computer for farther analysis. These can be used while the horse is in motion at any gait. With these sensors you will see a picture of the pressure is changing from 10 100 times a second. These systems are also calibrates so that the reading is the actual pressure in lb/in^2 or mm or mercury.
On the other hand they are very expensive - between 10,000 and 20,000 dollars (US). But this does give a fairly complete picture of the saddle to horse interface. There are several vets in the US that have a computerized saddle pressure sensor and it is very interesting to see the difference between a pressure pattern of static fit a then watch as it changes with the horse in motion. Some saddle companies are now designing their saddles using the aid of these sensors.
Mathematically, these relief impressions are the weighted average over the a period of time - the time defined by the "bandwidth" of the material of the pressure measured by a physical material. It is a one time readout of this average. It is a good start, but it is not the complete story. If a person is interested in getting a good saddle fit, then the Impression Pad is a good first start. But, if there are any questions left and they happen to be at a place where there is a computerized system, I'd recomme that they have their horse/saddle tested in motion to get a more complete picture of both the static and dymanics of the saddle/horse interface.
Off to a ride.
Cheers,
TrumanGreg Roskies wrote:
Dear Truman,
I am the inventor of the Impression Pad. I found your post interesting but with all due respect, not very accurate. Please correct me if I am wrong but according to our records you have never purchased an Impression Pad so I presume you have never had the opportunity to try one.The Impression Pad does do exactly what it is designed to do; it will show a relief pattern based on saddle pressure. It works on exactly the same principle as a dental impression.
One of our Impression Pad customers is the British Society of Master Saddlers in England. In a recent conversation with their veterinary advisor, P Stewart Hastie, MRCVS, he explained to me the problem Cambridge University was having with their computerized saddle fitting system. When they try to take a saddle fit reading while the horse is in motion too much data is generated by the sensing pad making the results difficult to determine. Also, the thickness of the sensing pad on the computerized system artificially jacked up the saddle, changing its fit.
Regards,
Greg Roskies
The Port Lewis Workshop--
Vertex Engineering, Inc.
Innovative Solutions
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