The question is when was the first system using servo-control motors
developed to regulate electric motors? A description of servo control
technologies can be found at http://www.a-m-c.com/what_is_a_servo.htm.
This definately happened before 1919, as in this year they were used
in maintaining constant relative speed of several motors in paper
machines (which I believe were built by G.E.), but I don't know the
exact application and date. A satisfactory answer would list the date
(at least year), the technical application and perhaps the inventor or
inventor's company. The answer *must* include a source for a citation.

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Request for Question Clarification by pafalafa-ga on 13 Sep 2004 17:39 PDT

Hi Brent.

It's a bit hard to tell, sometimes, which emerging technologiew would
actually be called a servo these days (the term itself seems to come
into being around the 1920's as "servomechanism") but here's one early
candidate anyway:

==========

Application filed March 20, 1880. (No model.) 

To all whom tt may concern:

Be it known that I, THOMAS A. EDISON, Of Menlo Park, in the county of
Middlesex and State of New Jersey, have invented new and useful
Improvement in Electro-Motors, (Case No. 2075) and I do hereby declare
that the following is a full and exact description of the same,
reference being had to the accompanying drawings, and to the letters
of reference...marked thereon.

In using clectro-motors, especially for actuating light machinery, it
is very desirable that the rate of speed of the actuated machine be
under control of the Operator, and that the means of control be
simple, effectual, and easy of application. Hitherto this has been
attempted only through controlling the electric circuit to the motor,
breaking or closing it in whole or in part. This breaking of the
circuit is destructive of the contact-points, and ordinarily effects
only starting and stopping of the machine, and does not regulate the
speed of the machine while running. I propose to control the speed of
the driven maachine without affecting the motor by the means more
fully hereinafter described and claimed...

[what follows is text linked to the drawings submitted with the patent
giving the details of the electro-mechanical control of the motor
speed, and then further text-only descriptions of the patent claims]


What I claim is- 

1. The combination, with an electro-motor, of a mechanical brake,
adapted to control the speed of the actuated machine, connected to the
motor through a pulley fastened to the...shaft of the motor by
friction, substantially as set forth.

2. The combination, with an electro-motor, of a brake applied to the
main driven wheel and controlling the speed of such wheel, but not
that of the motor, substantially as set forth.

3. The combination, with an electro-motor, of a friction-pulley on the
rotating shaft of the motor and a brake applied to the main driven
wheel and adapted to control its speed, substantially as set forth.

This specification signed and witnessed this 10th day of March, 1880. 

THOMAS A. EDISON.

==========



What do you think?  Does it sound like a servo?  

Looking forward to hearing back from you.

pafalafa-ga


P.S.  The original patent can be viewed online in its entirety at the
Patent Office website.

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Clarification of Question by brentdg-ga on 13 Sep 2004 18:10 PDT

Hi,

Thanks for your response. I do appreciate that it may not have been
called servo at the time. The patent you identified is intriguing, but
not a servo control system, rather it appears to describe a mechanical
control system. In the servo system, a small generator would be
attached to the load-bearing motor, the voltage of which would
fluctuate with the speed of the motor, which would in turn fluctuate
with the load on the motor. This information was then used to
manipulate the motor's controls to increase its speed. The entire
system was self-regulating.

-Brent

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Request for Question Clarification by pafalafa-ga on 13 Sep 2004 19:11 PDT

Thanks...that feedback helps a lot.  But it's still pretty hard to
pinpoint the very first servo mechanism.

A lot of effort was put into automatically regulating the output of
generators powering electric light systems.  For instance, here's a
description from on patent dated 1880:


Automatic regulator for electric light circuits

Having thus described my invention, what I claim as new...is

1. In an automatic electric-light regulator and distributing system, a
regulator in which the electric current is automatically increased and
decreased, according to the resistance of the lights, by the action of
one or more motors in a local circuit, said motors actuating a
rotating switch, substantially as described.

2. ...a series of contact plates, each in connection with a coil of an
electro- magnetic generator, said coils being adapted to be rendered
active and thrown into the main-line circuit by the movement; of a
rotating switch actuated by an electro-motor...



I know it's just a snippet, but does that sound any closer to what
you're looking for...?

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Clarification of Question by brentdg-ga on 14 Sep 2004 07:20 PDT

No, that sounds like a rheostat. The technology I am refering to is of
a generator that is used to regulate the speed of *motors*. I suspect
that you are looking too early - I would be surprised if this was
developed before 1890, and perhaps later - but again, I am not really
sure.

I am infering this because I know that a paper machine was installed
in 1909 without servo-control, but in 1919 with. It seems to me that
if it was available, it would have been used in 1909.

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Request for Question Clarification by pafalafa-ga on 15 Sep 2004 04:43 PDT

Hello,

I had understood the generator patent to be controlling the speed of
the generator itself, and it seemed to provide a servo function in
that capacity, but I confess to a large measure of uncertainty about
my interpretation, so....on we go.

This patent below, from 1912, is titled "A System For Controlling
Electromotors" and directly references paper-making machinery:


=====

This invention relates to improvements in a system for controlling
electromotors by means of the Leonard connection. And it consists in
the matters described hereinafter and particularly pointed out in the
appended claims.

For the purpose of explaining the invention several examples embodying
the same have been shown in the accompanying drawings...Figure 1 is a
diagram illustrating the effect of a compound winding in a "Leonard
connection, whereby an electromotive force is produced which balances
the electromotive force consumed in the resistances of the system...

As is, well known in the art, by means of the Leonard connection the
speed of electroMotors can-be regulated within large limits, and the
said regulation is almost independent of the load of the motor,
because the electromotive force of the starting dynamo is increased at
a rate which is proportional to its excitation. This regulation which
is sufficient in most cases is affected merely by the residual
magnetism of the starting machine and by the loss in the voltage which
takes place in the starting machine, in the circuit, and in the
armature of the driving motor.

In most cases the effect of these influences is very small. But in
some cases in which the [illegible] must be very accurate, for example
in motors for driving paper making machines, motors for driving
armored turrets, and the like, the said influences are
objectionable...

The object of the present improvements is to provide a system in which
the aforesaid injurious influences are avoided. For this purpose a
controlling device is provided which independently of the main current
tends to hold the speed of the driving motor exactly equal to the
value which it must have [illegible] reason of the excitation of the
shunt field, and which in case of a divergence automatically regulates
the shunt field...

=====

The "Leonard connection?....?  Not sure what that's all about.  Are we
getting closer...?

Let me know.

pafalafa-ga



P.S.  The illegible sections are due to poor OCR recognition, but I'll
be able to fill them in when I view the actual images of the patent.

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Clarification of Question by brentdg-ga on 15 Sep 2004 08:59 PDT

That sounds closer, It is difficult to tell from this description how
that technology works. I would imagine that one could tell from a
diagram without any trouble (as the sevo motor would appear on the
circuit.). I have no idea what Leonard connection is, but the text
clearly states that this technology is inadequate for paper, so it is
not what we are looking for.

It is the last paragraph that is intriguing, as it claims that there
is a solution, but it doesn't say what it is. I guess is would depend
what comes after that.

I note that the timing seems realistic. A system to regulate paper
machines appeared on the market in 1919, considering that the time in
the middle was WWI, it is plausible that the solution appeared in 1913
and it took 6 years to commercialize it.

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Request for Question Clarification by pafalafa-ga on 15 Sep 2004 14:52 PDT

Well heck, then.  Take a look at the actual patent and let me know what you think:


http://snipurl.com/93ju


Click on the "Images" button to see the actual patent -- you might
have to download the site's TIFF viewer in order to open up the file.


By the way, you wrote that "...but the text clearly states that this
technology is inadequate for paper, so it is not what we are looking
for...."  But the patent is actually FOR paper machinery, so I'm not
sure what you're referring to.  Take a look at the full patent and let
me know what you think.

Thanks.

pafalafa-ga

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Clarification of Question by brentdg-ga on 17 Sep 2004 07:24 PDT

That looks like a servo mechanism indeed. Is there any way to know if
this was the first variation? I noticed that there were not patent
citations on the patent as they do today. I would appreciate your
opinion.

That said, I believe that this satisfies my request.

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Request for Question Clarification by pafalafa-ga on 17 Sep 2004 07:37 PDT

brentdg-ga,

Great!  I'm glad we got the "servo-ness" of that patent established.  

One more question for you, if I may.  It sounded from several of your
comments that you're really looking for the first servo patented for
paper machines (rather than for just any type of electric motor).

Am I correct in this?  If so, I believe the 1912 patent is probably
the first in this regard.  But if you're not restricting the search to
paper machines, then there might be some earlier precedents
(including, perhaps, some of the earlier devices used to regulate the
speed of electic generators that I've already mentioned).

Let me know, and I'll be happy to see if there's a bit more history I
can uncover on this topic.

pafalafa-ga

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Clarification of Question by brentdg-ga on 17 Sep 2004 09:32 PDT

That would be great. I am particularly interested in paper machines,
but more general information on servo-generators would be most
helpful. The goal is to determine when it was technologically feasible
to electrify paper machines. It would be perhaps more interesting to
see if there were similar patents in the next few years as well,
perhaps assigned to Westinghouse or GE.

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Request for Question Clarification by pafalafa-ga on 17 Sep 2004 09:40 PDT

Hello again Brent,

I hope you won't think me overly persnickety, but you now have, by my
count, three requests on the table:

1.  Earlier paper-machine servos

2.  Earlier servos, any sort of machinery

3.  Later patents for paper machine servos, especially to GE/Westinghouse.


Please let me know which one of these I should pursue in order to
close this question.

If you're genuinely interested in having all three researched, I would
suggest posting a follow up question, after your current question is
answered.

Looking forward to hearing back from you.

paf

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Clarification of Question by brentdg-ga on 17 Sep 2004 11:37 PDT

You are not persnickety, I believe I was being unreasonable.
If we could just confirm that there were no other general servo
applications with a reasonable level of certainty, that would close
out the question.

I agree that a second (or third) posting is in order for the others.

-Brent

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Request for Question Clarification by pafalafa-ga on 17 Sep 2004 13:08 PDT

Brent,

I think we're getting close.

I cannot find any patents for paper machinery with an earlier date
than 1912 that reasonably looked like a servo to me.

Some of more general patents *MAY* be relevant although they don't
involve paper machines.  Two that came to my attention are these, both
from 1909:


http://snipurl.com/957t

http://snipurl.com/9586


The second one makes mention of the Leonard connection, again!



Have a look and see what you think.  If those are non-servo
technology, then I think the 1912 patent I mentioned earlier is
probably the one you're looking for.


Let me know your thoughts.


persnickety paf

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Clarification of Question by brentdg-ga on 22 Sep 2004 07:30 PDT

Pafalafa,

Sorry for the delayed response. These patents appears to be
predecessors but do not appear to be a standard servo circuit, as the
later patent does.

In the meantime, one of your competitors may have identified a servo
from 1904. Let me investigate whether that is a false alarm, otherwise
I am satisfied with your answer.

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Request for Question Clarification by pafalafa-ga on 22 Sep 2004 07:33 PDT

OK, Brent.  I must admit, I'm curious to learn what you come up with
up, so please report back after you've checked the 1904 reference, and
let me know if I should post my information as an answer to your
original question.

Thanks.

pafalafa-ga

This may not be exactly what you require but it does indicate that
servo systems go back way before 1919.

I have a set of 5 volumes ?Electrical Installations? by Rankin Kennedy
dated 1903. Lovely line drawings and remarkably readable. Fascinating
books which illustrate that a lot of the clever stuff was done a long
time before generally appreciated. They are apparently still available
at reasonable price, perhaps £50 or £60 for a set. Real bargain. I?d
lend you mine but I?m in Scotland.

Anyway, volume 2, page 120, describes methods of speed regulation in
response to varying load and voltage............

?This can be done automatically by several devices, one of which is
here shown (Fig.146), designed for maintaining a constant voltage;
they balance fluctuations due to variations of load, or of the speed
of the driving engine. These variations should not exceed about 10 per
cent. above or below the normal rates. The regulator consists of a
powerful solenoid and an iron core. The iron core is suspended from a
pivoted arm and balanced by a counterweight, and carries an ebonite
trough containing mercury. The resistance helices terminate in
straight ends, which are arranged in a formation of steps projecting
downwards into the ebonite trough. When the voltage rises or falls the
iron core is sucked down by the solenoid or raised, carrying with it
the trough of mercury. As the level of the mercury rises or falls, a
greater or smaller number of wire ends are immersed, whereby more or
less resistance is short-circuited or inserted until the normal
voltage is restored.
An adjustable glycerine dashpot at bottom of the solenoid prevents
violent movements of the core? etc.

Also described (in vol IV) is automatic solenoid regulation of arc
lamps. There may be direct refs to your exact requirement but I?d have
to trawl through all the vols ?cos indexes aren?t too wonderful. But
given that regulator technology goes way back to steam regulator days,
including the maths for loop response speed, I would expect that such
systems were around in late nineteenth century.

I can post cryptic email address if you want more info from books.

Best

Thanks,

It appears that this is not precisely what I was looking for as the
system uses a solenoid as opposed to a servo-generator. My guess is
this was an attempt to solve the same problem that was less
successful.

Although I don't know, I would bet that the servo-generator system
appeared later, and that there were many solutions suggested, this
being one of them.

The books sound intriguing. I would be interested if any of the
control systems described a little generator attached to the main
motor for speed regulation.

-Brent

Re the books, I shall do my library reading (the toilet) on them. If I
find anything relevant I'll let you know.
I presume you are aware of the system which synchronises the rotation
of a motor with a generator -- the generator being hand cranked. Like
coupling stepping motors. Seem to recall it being used very early on
remote gun aiming systems in ships. But again, that?s not exactly what
you seem to seek. Interesting nevertheless.

Best

Hi again. I think perhaps I have found one of the things you were
looking for (1902) Vol III, page 193.

?The method employed for overcoming the instability in the speed of
the rotary when driven as a direct-current motor is to excite the
rotary by means of a small generator, which is driven from the rotary
itself. Tappings are taken from the three-phase side of the rotary to
a small induction motor, which is directly connected to a small
continuous-current generator. This generator works low down on the
characteristic curve, and is unsaturated at the normal electromotive
force. Any change in the speed of the rotary, therefore, causes a much
greater change in the electromotive force of the exciter, and this
varies the field of the rotary, and keeps the alternations constant
independent of the nature or amount of the load. The small exciter set
is shown in Fig. 185. The exciter generator has a normal 220 volts
with a current of 5 amperes. Arrangements had to be made for putting
the rotating field coils in two parallel sets when excited in this
manner.?

There?s a page or so more on the system, then it goes on to optical
synchronisation! If you want the rest of it I?ll do an OCR. As I said,
books are not too expensive and I think there are 5 in the series.
Just to sicken you, I got the books and three sets of other ancient
lovely techy books for £5 at an auction.

Best

I agree that what you described on Sep. 17th appears to be a servo. If
you could OCR or even send me an image of these pages that would be
fantastic. Please, if you can, include the full citation.

(BTW, I tried to see if they were available on amazon, and they were
around $35/volume plus shipping. Getting the whole set for $5 was
certainly a steal. Lucky you!

I did order one of the volumes through interlibrary loan here at my
university, so I hope to be able to take a look.)