Electric Valves
By John Grant
Hi Robbie,
Thanks for your detailed response to my previous message. I have interspersed some comments below:
On Sat, 30 Dec 95 14:11:27 PST Robbie Rhodes wrote:
> to: ir004161@pop3.interramp.com (John R. Grant)
> cc: rolls@foxtail.com (Automatic Music Instrument digest)
> de: rrhodes@foxtail.com (Robbie Rhodes)
> date: 30 December 1995
>
> Subject: Electric valves
>
> John, I'm glad you enjoyed the translation of the article:
>
> Juergen Hocker, Horst Mohr, Walter Tenten: "Computer Control and
> Synchronization of two Ampico Self-playing Grand-pianos", in
> "The Mechanical Music-instrument", Nr. 63 (August 1995) p. 42-48,
> published by the Society for Self-playing Music Instruments (GSM),
> Germany.
>
> The writers say that many valve designs were studied, including yours,
> but none met all their requirements. I think that they rejected your
> solenoid valve design because of concerns about power consumption,
> repetition rate, consistent response from valve to valve, and
> adjustment stability.
++++++++++++++++++++++++++
Well, they didn't exactly "reject" my design, they (Herr Hocker, et als) simply did not participate in my initial valve subscription offer last year. I also had some concern about the power consumption which, at three watts, is close to the limit that the Devtronix and SC Engineering MIDI circuitry can handle without going to intermediate driver stages. This is the main reason that I was planning to go to a 24 VDC solenoid instead of 12 VDC. This reduces the current draw through the driver devices by a factor of 2 and the power dissipated by a factor of 4 (I squared R loss). Interestingly, no one who obtained sets of the valves from the first subscription has mentioned any problems with them. I did not receive from Herr Hocker any test results he may have run on the one sample unit I sent him. This is one reason I'm interested in the independent test program you have proposed.
++++++++++++++++++++++++++
>
> Consider the difference in armature masses between (1) a solenoid,
> (2) an ordinary relay, and (3) an organ "magnet" valve, such as the
> Reisner design. ("Armature" is the moving piece in any magnetic
> device like these.)
>
> In order to realize similar transit acceleration, the force of the
> return spring must be proportional to the armature mass. Recall the
> familiar equation, "force = mass x acceleration".
>
> The return-spring of a solenoid valve does not have very good
> stability because of high force and large compression percentage --
> after many cycles of operation, and heating and cooling, the spring
> force is likely to change. This will degrade the consistency of the
> valve-to-valve response times. Also, the sliding armature of a
> solenoid is very susceptible to contamination, hence varying friction.
> I can't recall solenoid valves being used in any industrial application
> which requires long-term stability like in a reproducing piano.
+++++++++++++++++++++++++
I don't see that there is any fundamental difference between a "solenoid operated valve" (such as mine) and solenoids (successfully) used in a striking mode such as the PianoDisc/Pianomation/Pianocorder designs. While each of these have differing problems and limitations, I believe the toughest thing to "get right" is consistency from unit to unit considering that you are asking them to produce a RANGE of forces which may be affected by heat build-up/duty cycle. In an application where the same voltage is being applied to each unit, force per se is relatively unimportant as long as you have the minimum necessary to crack the valve. Here the parameter most likely to be affected is response time. My "gut feel" is that this variation, on a percentage basis, is probably no worse (and may be a good deal better) than the "normal" variation found among pneumatic valve response times, which as we all know, can vary TREMENDOUSLY. Even response time per se is relatively unimportant PROVIDING the "time to open" and the "time to close" are essentially equal so that no "smearing" of the applied signal takes place.
++++++++++++++++++++++++++
>
> The basic requirement of an electric valve for a reproducing piano is
> only to open a tiny aperture to a hose, from 4 up to 40 (Ampico) or 70
> (DuoArt) inches-of-water vacuum. There is no need for the long stroke
> and "brute force" of a solenoid, nor for the large port area which a
> relay armature can cover. Therefore, the organ-style "magnet valve"
> (such as supplied for many decades by the Reisner company) is adequate.
> It has other deficiencies, though.
+++++++++++++++++++++++++
I didn't know they made a "vacuum style" valve. Is it similar in design to a standard organ chest magnet valve (which, of course, operates on pressure.)?
+++++++++++++++++++++++++
>
> The organ valve design sacrifices speed and magnetic path efficiency in
> favor of simplicity. The valve assembly is bulky, but the armature is
> tiny, and the return-force is gravity. The low efficiency results in
> high power dissipation, but this is not a problem due to the great area
> of the exposed coils, and in an organ there is plenty of space for
> convection cooling. (And _inside_ the wind chest there's plenty of
> moving air!).
>
> The valve for a reproducing piano, as you correctly point out, must be
> both low-power and small. It must also be quiet! Author Walter Tenten
> told me that their valve assembly had to be contained in a solid, felt-
> lined box, in order to reduce the noise. Most of the air vents ultimately
> were covered, too, because of the noise. Fortunately, he said, the
> temperature of the relay valves didn't rise so high that a fan was
> necessary.
++++++++++++++++++++++++
Will your proposed test program address noise levels of the valves? Mine SEEMS to be very quiet, but I have no empirical data (nor any instrumentation to produce any).
++++++++++++++++++++++++
>
> The magnet valve designed by Wayne Stahnke for the IMI Cassette Converter
> improves the Reisner valve in these ways: (1) it's considerably smaller,
> (2) power dissipation is reduced, because a strap-steel frame forms a
> complete magnetic path with the armature disk, (2) the mass of the
> armature is minimal, and (3) a rather "long" return spring is used, which
> experiences only about 15% active compression.
>
> The extremely rare DuoArt Concertola has a magnet valve with even
> better efficiency, due to the steel cup enclosing the coil, but
> without a return spring it is slow compared to the Stahnke design.
> Also, all 98 valve components are assembled into single wooden
> board, much like a primary valve set from an Ampico, and this
> assembly is difficult to adjust.
>
> Mike Ames inquired about the cost of duplicating the Concertola
> valve, and was told it would be about $10 each in a small quantity
> (1000 units, I believe). A few years ago Ampico technician Randy
> Cox and I got a similar quote for a short run of Cassette Converter
> valves.
>
> All I know about the "new" Reisner valve is that the company is
> talking about modifying their old vacuum valve design to make it
> smaller (and less expensive, we hope). The "old" design costs only
> about $4.00 in 100 quantity, which is appealing, but otherwise it
> fails to meet other important requirements.
>
> All of the potential designs for a cheap reproducing piano valve
> seem to cost the same, and $10 per valve is still too much for me.
> The only apparent way to reduce the cost is through production in
> large quantities, like 10,000 units. We (that's Mike Ames, Randy
> Cox and, with advice from Wayne Stahnke) are studying all the
> possibilities.
> I agree with you, John, that a market is developing right now for
> good quality valves. You and I and many subscribers in this group
> are definitely planning to someday connect the computer to the
> piano, just as described in the German Society article.
+++++++++++++++++++++++++
As I previously mentioned to you privately, do we need to "inform" Reisner of the potential demand for a cheap, reliable vacuum valve? Would this possibly help speed up design and production? Whom should we call?
+++++++++++++++++++++++++
>
>
> I want to see all the options before I commit my meager funds!
>
> -- Robbie Rhodes
> +++++++++++++
AMEN!
++++++++++++++
--------------------------------------------
"Every creative act results from a sudden cessation of stupidity."
-Edwin H. Land, inventor of the Polaroid Land Camera
"Help stamp out and eliminate superfluous redundancy." -Genius
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(Message sent Sun 31 Dec 1995, 09:28:38 GMT, from time zone GMT-0800.) |
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