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BACKGROUND OF THE INVENTION
The present invention relates, in general, to pipe organs, and more
particularly to a system for electronically positioning the
volume-controlling shutters for a pipe organ swell chamber.
In pipe organs the various tones are derived from wind blown pipes. Each
pipe is capable of sounding at only a single intensity (volume) level; and
if an attempt is made to control the loudness, as for example by changing
the air pressure, an unacceptable variation in tuning will result. In
order to surmount this limitation, it is customary in a pipe organ to
place the pipes of at least some of the divisions of the organ in a box or
room called a (swell box or swell chamber) separated from the main
listening room by a set of moveable shutters (sometimes called shades).
When closed, these shutters effectively close off the chamber from the
listening room and substantially attenuate the sound that is heard. A
swell pedal (or swell shoe) is provided at the console and can be adjusted
to several positions for controlling the extent that the shutters are
opened. Patents that relate to swell shutters and swell boxes include U.S.
Pat. Nos. 500,040 issued to E. M. Skinner in 1893, and 2,005,643 issued to
H. Willis et al. in 1935.
In early swell devices the shutters were mechanically linked to the swell
pedal by means of operating rods or cables. With the development of
electrically controlled key actions it became common to place the console
at a remote location from the chambers, and it became difficult to arrange
the necessary mechanical linkage to the swell chamber shutters. The next
step was the development of electrically controlled pneumatic swell
shutter operators, an example of which is shown in U.S. Pat. No.
2,072,844. Such pneumatic devices have been employed for decades and have
been reasonably successful; however they have many limitations, the most
important of which is their large size. Pipe organs operate on low wind
pressures, and in order to achieve sufficient force to move the relatively
heavy shutters with promptness, operating pneumatics of great bulk are
necessary. In past decades wind pressures of up to 15 inches water gauge
were commonly used. This is in fact a relatively low pressure (about
one-half pound per square inch), and created problems in driving prior
swell shade operators. However, the problem of rapidly and accurately
moving swell shade operators is now greatly exacerbated by the current
trend back to the very low pressures used in early organs, where the pipes
speak on pressures in the order of one and one-half (11/2) or two (2)
inches water gauge.
Attempts have been made to make electric motor-driven swell shutter
operators, but none have been very successful because of one or more of
the limitations of cost, size or lack of precision in operation. An
example of such an operation is found in U.S. Pat. No. 3,701,833. A
successful swell operator must move the shutters promptly, but precisely,
without hunting, and without slamming as the shutters close. In addition
it must be easily adaptable to a wide range of shutter sizes and weights,
and must be easily adjustable to produce a smooth swell, whereby the
loudness of sound heard varies uniformly from soft to loud as the swell
shoe is moved from closed to open.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a swell
shutter operator which does not require air pressure for operation, which
is quiet, reliable, and accurate, and which can be operated from a
remotely located organ console.
Briefly, in accordance with the present invention, the swell shutters of an
organ are driven by an electric motor connected to a speed reducer
mechanism. Alternatively, the connections to the shutters can be made by a
cable together with a spring or weight return, or by other suitable
connectors. A conventional swell pedal having either stepped contacts or a
continuously variable resistive element is adapted to be operated by the
organist's foot in the usual fashion. A first variable potentiometer,
either in the form of a continuously variable potentiometer or in the form
of a resistor network, forms a voltage divider which delivers an output
voltage of a first given polarity, for example positive, the magnitude of
which is a function of the position of the swell shoe. Associated with the
output shaft of the speed reducer is a cam operated second potentiometer
which in its preferred form is a photoelectric potentiometer comprising a
moveable light emitting diode and a photo resistor mounted in a light
tight tube. As the output shaft moves, the resistance of the photocell
changes as the light emitting diode is moved closer or farther away from
the photo resistor by means of a cam attached to the output shaft. This
second potentiometer is connected to a source of potential of a second
polarity, for example negative, so that its output is a negative voltage
the magnitude of which represents the position that the shutters are in at
any given moment.
An electronic system of integrated circuit comparators is connected to the
outputs of the two potentiometers. The comparators compare the positive
voltage from the swell shoe potentiometer, which indicates the position
that the organist wishes the shutters to be in, to the negative voltage
from the second potentiometer, which represents the actual position of the
output shaft, and thus the shutter. These positive and negative voltages
must be accurately regulated to insure proper control of the shutters, and
thus they are obtained from an inverter circuit, followed by solid state
voltage regulators which stabilize the voltage to a high degree of
accuracy. The electronic logic circuitry responds to the two input
voltages and decides what action to take. In the event of an imbalance
between the voltages it will pull in an "enable" relay which enables the
motor to start and to move the shutters so that balance can be achieved. A
second relay controlled by the logic system simultaneously tells the motor
whether a forward or a reverse motor direction is required to correct the
imbalance. A third relay adjusts the speed of the motor so that when only
a small imbalance is sensed, the motor will run at a relatively slow
speed, while if the imbalance is great the motor will run at a faster
speed. Whenever the motor is not running, the enable relay drops out, and
additional, normally shorted contacts on the relay cause the motor to be
short circuited to provide dynamic braking, which stops the motor in only
a few revolutions.
In spite of the fact that the motor brakes quickly once balance has been
achieved, because of inertia in the mechanical system, it obviously is not
possible for the motor to stop in "zero" time, and some degree of
overshoot, therefore, is inevitable. To prevent this overshoot from
causing "hunting" in the motor, and thus causing the shutters to oscillate
about the desired position, dead bands are provided in the comparator
circuits to prevent operation of the balancing circuit. Thus, balance need
not be absolutely perfect, but need only be "close enough" as determined
by the dead band adjustments.
Since the amount of overshoot is partly a function of how fast the motor is
running, automatic means are provided for widening the dead bands whenever
the system is in high speed operation, and for causing the dead bands to
be narrower when the system is running slowly. There are several reasons
for this action to be designed into the system. One is that the need for
precise balance is only important when the shutters are near their closed
positions. In this range even slight differences in shutter position make
a noticeable difference in the sound level heard by the listener, and
hence it is important that the shutters assume substantially the same
positioning every time the swell shoe is moved into one of the near closed
positions. Further, when the shutters are near the closed position, it is
important that the motor run at its slow speed to prevent slamming of the
shutters as they approach their fully closed position, or to avoid
unnatural abruptness as they move toward a slightly opened position from
the fully closed position.
In order to accomplish these objectives the logic system senses the
magnitude of the error between the two potentiometer voltages, the
position of the shutters, and the direction in which they are moving, and
then operates the three relays in such a manner as to control the system
to produce all of the desired objectives.
The electric motor that drives the system is preferably a DC motor, and it
is an important advantage that it operates on the low voltage organ power
supply that is a part of all electrically operated pipe organs. Such power
supplies are commonly known in the trade as "rectifiers" and usually range
in voltage between about 12 volts and 15 volts. The use of the organ power
supply for this purpose avoids the need for extra power line wiring, and
results in substantial savings in the installation costs of the swell
shutter operator.
As previously mentioned, the sizes and weights of swell shutters vary
markedly in different organs as does the friction involved in such
systems. Thus, the exact nature of the linkage used to drive the shutters
(shades) may vary with different installations. In some cases a direct
linkage from the speed reducer output shaft is appropriate, while in other
cases operation by means of a cable and pulley arrangement is more
practical. In the latter case, the swell shade operator of the invention
can be arranged to pull the shutters open or to pull them closed, with the
force required to return the shades to the opposite positions being
supplied by a spring or weight system. When these latter systems are used,
it is clear that the load seen by the motor will be different depending
upon whether the spring or weight is pulling against the direction of the
motor, or is helping to accelerate the motor. Because of this, various
adjustments are provided to control the speed of the motor independently
when it is moving in the opening or in the closing directions. In
addition, other adjustments permit the overall motor speed to be adjusted
according to the load imposed upon it, and according to the voltage of the
organ rectifier to which the system is connected.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and additional objects, features and advantages of the
present invention will become apparent to those of skill in the art from
the following detailed description of a preferred embodiment, taken in
conjunction with the accompanying drawings, in which:
FIG. 1 is a perspective view of a swell shutter operator according to the
invention;
FIG. 2 is a schematic circuit diagram of the swell shoe potentiometer
circuit board assembly;
FIG. 3 is a schematic circuit diagram of the swell shade operator of FIG.
1; and
FIG. 4 is a schematic diagram of an inverter circuit for use in the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, FIG. 1 is a perspective view of a preferred form
of the swell shutter operator 10 of the invention. As illustrated, the
operator incorporates a DC electric motor 11 having an output shaft 12
connected to a speed reducer 13. The speed reducer has an output shaft 14
to which is connected a crank arm 15, the outer end of which carries a
connector 16 for use in connecting the output of the swell shutter
operator to the shutters, or shades, of a swell chamber (not shown). The
speed reducer is a conventional gear mechanism which reduces the speed of
rotation of motor shaft 12 by about 50 to 1 and causes the output crank
arm 15 to rotate either in a clockwise or a counterclockwise direction, as
viewed in FIG. 1, depending upon the polarity of the voltage supplied to
the motor.
Also connected to the output shaft 14 of the speed reducer is a position
indicator cam 18 which is connected to the shaft by a suitable set screw
and which is shaped to produce from a potentiometer to be described a
voltage which corresponds to the rotational position of shaft 14. A cam
follower 19 is secured to and supported by a wall 20 which forms a part of
a housing for motor 11, the cam follower being held in position by
suitable brackets 21 and 22. A coil spring 23 surrounds cam follower 19
and is mounted between bracket and a flange 24 on a first, contact end of
the cam follower so that the spring presses the cam follower into contact
with the camming surface of cam 18. A suitable bearing 25 is mounted
within bracket 22 to hold the cam follower so that as the cam 18 rotates,
the cam follower 19 slides laterally through the bearing 25.
The second end of the cam follower opposite to the contact end and spaced
from cam 18, passes through bracket 21 and rides in a tube 26 secured to
the bracket. The cam follower fits snugly in the near end of tube 26 so
that ambient light does not enter, the distal end of the tube being closed
by a photocell housing 28 mounted on the tube. The photocell is exposed to
the interior of tube 26, and the end of the cam follower carries a light
emitting diode (not shown) which is connected by leads 29 to a terminal
block 30. The light emitting diode rides in tube 26 with the cam follower
19, sliding back and forth in a horizontal direction as viewed in FIG. 1
as the output shaft 14 rotates, and moving toward and away from the
photocell.
The photocell 28 is a photoresistor whose resistance varies as a function
of the light intensity impinging on its surface. Because the photocell is
exposed only to the interior of tube 26, the intensity of the received
light is a function of the distance between the light emitting diode
carried on the end of the cam follower and the surface of the
photoresistor 28. Thus, the cam follower arrangement provides a varying
light intensity at the photocell and produces a varying output voltage
from the photocell which corresponds to the rotation of shaft 14, and thus
to the position of crank arm 15 and the corresponding position of the
swell chamber shutters connected thereto.
The motor 11 and speed reducer 13 are mounted on a base plate 32, with
upstanding end plates 33 and 34 and a suitable cover (not shown)
completing the swell shutter operator housing.
Mounted within the swell shutter operator housing is an inverter
transformer 35, resistors 36 and 37, and terminal strips 38 and 39 which
facilitate connecting the unit into an organ system, and also facilitate
adjustment of the unit for proper operation under various conditions of
service. A main electronic circuit board assembly 40 is mounted on base 32
and contains the logic and control systems for the motor 11. A series of
potentiometers generally indicated at 42 are mounted on the circuit board
so as to permit adjustment of individual electronic logic circuits to be
described hereinafter. A fuse 43 protects the system from damage due to
the failure of any components, and mounting gromets 44 in the base plate
32 are for the purpose of mounting the complete unit to a wall or floor
location which permits mechanical connection of the unit to the shutter
assembly and electrical connection to the organ console.
A relay housing 45 encloses the various relays to be described in
connection with the circuit diagram of FIG. 3, and provides acoustic
isolation so that the operation of the relays is not heard.
A more detailed description of the system which has been outlined in the
foregoing discussion of FIG. 1 will now be given in connection with the
description of the schematic diagrams of FIGS. 2 and 3. FIG. 2 is a
schematic circuit diagram of a position adjust board generally indicated
at 48. This is a separate sub-assembly which is customarily mounted at the
organ console, and is connected to the conventional organ swell pedal 50
to function essentially as an adjustable potentiometer for producing an
output signal at line 51, the magnitude of which represents the position
of the swell pedal 50. The conventional pipe organ swell pedal consists of
a number of contacts, 52, 52a, 52b . . . 52g which usually are in the form
of silver wires that are sequentially contacted by a rotor shown
schematically at 53. The rotor and contacts comprise a rotary switch
which, in the position shown, correspond to a swell pedal location which
requires the swell chamber shutters to be closed. As the pedal 50 is
depressed by the organist's foot, the switch rotor 53 sequentially engages
the contacts until it reaches contact 52 g, which corresponds to the full
open condition for the swell shutters. Each of these switch positions is
connected to a lamp circuit which includes a resistor 54 and a light
emitting diode 55. The purpose of these lamp circuits is to indicate in
what position the swell shoe is located, so that the adjustment procedures
for the shutter operator system can be carried out in an orderly fashion.
Also connected to each switch position in parallel with the foregoing lamp
circuits is a potentiometer 58 for establishing at its output terminal 59
a potential which is determined by the potentiometer adjustment. Each of
the output terminals 59 is connected by means of a corresponding diode 60
to an output buss 62, upon which will appear a voltage corresponding to
the setting of the potentiometer 58 which is contained in the circuit
connected to the contact selected by switch arm 53. If a shorting type
switch is used, the voltage on buss 62 will be the highest voltage to
which any of the simultaneously activated potentiometers 58 is adjusted.
Buss 62 is connected through load resistor 63 to ground, and through
resistor 64 to the input of an operational amplifier 66, which is
conventional, and which may be a National Semiconductor type LM741. This
operational amplifier and its related circuitry acts as a level translator
and produces at its output 51 a negative voltage, the magnitude of which
will indicate the position of the swell pedal 50. The operational
amplifier is connected in an inverting configuration, and accordingly the
positive voltage connected to the rotor arm 53 is converted to a negative
voltage. Bias to the non-inverting input terminal 68 of the amplifier 66
is supplied by an adjustable potentiometer 69 which is adjusted to
reference the output voltage from the operational amplifier on line 51
with respect to common ground. Resistor 71 and capacitor 72 provide
negative feedback around the operational amplifier for stable operation.
In setting up the swell shutter operator for use with a pipe organ, the
potentiometers 58 through 58g are individually adjusted to determine the
exact extent of the swell shutter opening desired for each position of the
swell pedal 50. The proper adjustment of these potentiometers would be
such as to produce at the output terminals 59 through 59g progressively
higher output voltages at each step as the pedal is moved from its closed
position to its open position. The output signal on line 51 thus will be a
voltage the magnitude of which represents the position that the swell
shutters are to be in at any given setting of the pedal 50. This signal
provides one input to the comparator system to be described, while the
second input signal is produced by the cam position sensor described with
respect to FIG. 1; i.e., the output from photocell 28.
Referring now to FIG. 3, which is a schematic diagram of the logic circuit
for operating the swell shutter operator of FIG. 1, there is illustrated a
first input line 51 which receives the output from the position adjust
board 48 just described. A second input is provided by a cam position
sensor 73 which includes a light emitting diode 74 and the photoresistor
28, the light emitting diode being mounted on the cam follower 19 as
described above with respect to FIG. 1. As previously described, as the
lamp 74 is moved closer to or further away from the photoresistor 18, its
resistance changes. Photoresistor 18 is connected to a resistor 75 to form
a voltage divider, the junction of resistors 18 and 75 being connected to
the base of an emitter follower transistor 76. Substantially the same
voltage appears across the load resistor 77 of transistor 76 which
provides a low impedance source for driving the various comparator
circuits to be described. The purpose of the comparators and logic system
of this figure is to compare the voltage from the position adjust board 48
that appears on line 51 with the output from the cam position sensor which
appears across load resistor 77 on line 78, and to control the shutter
drive motor 11.
It is important that the DC bias voltage (plus or minus 12 volts) supplied
as DC input voltages to the swell pedal switch 53 (FIG. 2) and to the
photoresistor 18 be very stable and well regulated. In a preferred system,
these voltages are obtained from the organ rectifier by means of an
inverter circuit generally indicated at 80 and illustrated in FIG. 4.
Referring now to this figure, the inverter circuit includes a
multivibrator comprised of transistors 81 and 82, resistors 83 and 84, and
capacitors 85 and 86. Power to this circuit is provided by the organ
rectifier (not shown), the positive terminal of which is connected through
diode 88 and resistor 89 to the center tap of the primary winding of the
inverter transformer 35. The outer ends of the transformer primary winding
are connected to the collectors of transistors 81 and 82 so that as the
multivibrator circuit oscillates at a frequency determined by the value of
capacitors 92 and 93, the transistors 81 and 82 alternately switch the
ends of the transformer winding to the minus terminal of the organ
rectifier through the emitter connections of the respective transistors.
This switching of the transformer primary connections produces an AC
current in the primary winding which is transformed to the secondary
winding. The secondary winding is also center tapped, and is connected at
its outer ends to a rectifier circuit comprised of diodes 96, 97, 98 and
99 which produce positive and negative DC voltages across capacitors 100
and 101, respectively. These voltages are applied to the integrated
circuit regulators 102 and 103, respectively, which regulate and stabilize
these voltages which then appear at the plus 12 and minus 12 volt
terminals. The positive voltage regulator may be an LM340+12 and the
negative regulator may be an LM320-12 both manufactured by the National
Semiconductor Corporation.
Referring again to FIG. 3, 106 is a comparator, which may be made from an
integrated circuit operational amplifier such as the LM741 previously
mentioned. All of the comparators to be described hereinafter are made
from this same type integrated circuit. The comparator 106 receives two
input voltages, one of which is from the swell shoe potentiometer, whose
voltage output appears on line 51, and which is connected through diode
107 and resistor 108. The second input signal is from the cam position
sensor 48, which appears on line 78, and is connected to the input of the
comparator through diode 109 and resistor 110. These input voltages are
compared, and if the negative voltage from the cam position sensor 73 is
of greater magnitude than the positive voltage from the swell (or
expression) shoe potentiometer 48, the comparator 106 will produce a
positive voltage at its output terminal 111. Accordingly, this comparator
is called the "negative imbalance sensor".
Resistor 113 and potentiometer 114 are a bias network that biases the
non-inverting input terminal 115 of the comparator to a slight negative
voltage as adjusted by potentiometer 114. The purpose of this circuit is
to produce a dead band, for the purpose previously described, wherein the
amount of negative imbalance must be above a minimum threshold as set by
potentiometer 114 in order for the negative imbalance to be recognized as
significant enough to cause the circuitry to correct the imbalance by
moving the swell shutters. Capacitor 117 is used to prevent parasitic
oscillation of the comparator circuit.
Comparator circuit 118 is similar to that just described, except that the
inverting and non-inverting inputs are reversed. The input signal from
line 51 is through diode 119 and resistor 120, and the input signal from
line 78 is through diode 121 and resistor 122. This comparator produces a
positive voltage on line 124 whenever a positive imbalance occurs,
provided that the positive imbalance is greater than the off-set voltage
applied to terminal 125 as determined by the resistor 126 and the
potentiometer 127, which provide positive dead-band adjustment. This might
also be called the "closing dead-band adjustment", because whenever the
imbalance at the input of this comparator is positive, it means that the
shutters are to be moved in the closing direction in order to correct the
imbalance. In like manner, the potentiometer 114 previously described can
be properly characterized as the "opening dead-band adjustment" control.
Thus we see that if there is either a positive or a negative imbalance
between the cam position sensor voltage and the swell shoe potentiometer
voltage, and if the imbalance is greater than the off-set dead-band
adjustment voltage, then one or the other of the comparators 106 or 118
will produce a positive voltage at its output.
A positive output on line 124 from comparator 118 is applied through diode
128 and resistor 129 to the base of a motor enable transistor 130. The
collector of transistor 130 is connected to the operating coil of a motor
enable relay 131. A positive voltage at the output of comparator 106 is
also applied to the same transistor 130 input via diode 132 and resistor
129. However, whenever there is a positive voltage at the output 111 of
comparator 106, this voltage is also applied through resistor 133 to the
base of reverse circuit transistor 134, the collector of which is
connected to the operating coil of a reverse relay 135. When the motor
enable transistor 130 is switched on, the coil terminal 136 of relay 131
is connected through the transistor to the organ rectifier (-), and since
terminal 137 of this coil is connected to organ rectifier (+), this relay
will pull in and start the motor 11. Whenever the output of comparator 106
is positive, the reverse circuit transistor 134 conducts and connects the
terminal 138 of the reversing relay 135 to organ rectifier (-). Since the
opposite terminal 139 is permanently connected to organ rectifier (+), the
reversing relay 135 will also pull in, reversing direction of the current
through the motor and causing it to run in the reverse direction. The
diodes 140 across the relay coils are protective diodes to prevent strong
transient voltages, that would otherwise arise due to the collapsing
magnetic fields around the coils, from causing damage to the various
switching transistors.
Whenever the motor enable relay 131 is in its unenergized condition, there
is a short circuit placed across the motor 11 by means of the contacts 141
and 142 of this relay. This is for the purpose of providing dynamic
braking, for with the motor short-circuited, it will stop rotating very
quickly. This is important to minimize hunting, and to enable precision
operation of the system.
Unlike the other comparators in this system, comparator 144 has only a
single input, which is from line 78 through diode 145 and resistor 146. A
potentiometer 147 establishes an off-set voltage which is applied through
resistor 148 to the non-inverting input of the comparator. It should be
remembered that the voltage at point 78 is always a negative voltage and
that the magnitude of the voltage is a function of the position of the cam
position sensor, which is in turn a function of the position of the swell
shutters. Whenever this negative voltage exceeds the threshold set by
potentiometer 147, comparator 144 produces an output at line 150, and this
positive voltage is applied through diode 151 and resistor 152 to the base
of a slow speed transistor 153, the collector of which is connected to a
terminal 154 of a slow speed relay 155. Conduction of transistor 153
connects terminal 154 to organ rectifier minus, and since terminal 156 of
the relay is always connected to organ rectifier (+), the relay will pull
in and cause the motor to slow down whenever the swell shutters are in a
nearly closed position.
Slowing of the motor is accomplished as follows: diodes 157 and 158 are
connected to relay 155 and form a nonpolar diode network which reduces the
applied voltage according to the number of diodes through which the
current must pass, since each diode causes a fixed voltage drop of about
0.7 volts. Jumper connectors 160, shown in dotted line form, can
optionally be connected to short out various diodes to make this voltage
reducing diode network more or less effective, as required. Whenever the
slow speed relay is in its unenergized position, the relay contacts 161
and 162 cause the complete diode network to be shorted out, and therefore
ineffective, but when the slow speed relay is energized, these contacts
are open and the diode network is made effective to slow the speed of the
motor. This then, causes the motor to always run at slower speed when the
shutters are in their nearly closed position, the exact point at which the
slow down occurs being determined by the setting of potentiometer 147 at
comparator 144.
There is a condition, however, when the shutters are near their closed
position but it is not desireable to have the speed slowed. This is the
condition where the imbalance is such that the swell shutters must move
toward their open position, and when there is a large imbalance, meaning
that the swell shoe is calling for the shutters to go to, for example, the
fully opened condition. Under these conditions the shutters should not
move slowly, but rather should proceed at high speed. To accomplish this,
a circuit including the comparator 164 is provided. This comparator is a
duplicate of comparator 106, except that the offset voltage a | | |
