Telescope dome rotation system

The invention is a system for controlling the operation of a dome in connection with a telescope in order to maintain the slot of the dome in alignment with the telescope at all times so that stars may be viewed continuously. The system eliminates of minimizes the need for the user having to manually control the operation, usually rotation, of the dome. Preferably four infrared sensors and transmitters are mounted along the circumference of the telescope in order to send signals to a controller when the edge of the dome is detected which occurs when the signal is reflected back to the sensor. Each of the sensors should be 90.degree. in relation to each other. Each of the sensors is in connection with a controller. The controller is in connection with the movement system of the dome and sends signals to the movement system that rotate the dome until the sensors determine that the dome slot is aligned with the telescope.

BACKGROUND AND FIELD OF THE INVENTION 
The dome control system described herein relates to the field of 
astronomical domes associated with telescopes and, especially, to those 
domes that must be rotated in order to keep the vertical dome slot, or 
aperture, in alignment with the telescope. Such dome control systems may 
be operated manually by the user in order to keep the telescope in 
alignment with the aperture of the dome. Many telescopes nowadays can be 
moved themselves, either manually or by automatic control. Because the sky 
is always moving to an observer on earth, such controls are necessary if 
the telescope is to follow the movements of a celestial body throughout 
the evening. 
An astronomical telescope is usually installed in a rotatable dome having a 
slot (may be referred to as an aperture). Such telescope is aimed through 
the slot in order to follow, for example, a star. As the earth turns, the 
telescope turns to follow the star. As the telescope turns, the edge of 
the dome slot will eventually interfere with the view, thus requiring the 
dome to be turned. The turning may be done manually, or by electric motors 
activated by manually operated switches or under computer control. It is 
contemplated that the system described herein will find its greatest 
utility in connection with smaller domes and associated control systems 
that are directed toward small scale research applications but the system 
is not limited to such uses. 
Providing a dome that can be automatically operated would eliminate the 
time and trouble needed to manually control the dome rotation and also 
allow for continuous viewing of the heavens on a long term basis, say an 
entire evening, without the viewer having to go out to the dome at 
intervals throughout the night in order to keep the dome aperture in 
constant alignment with the telescope. 
The electronic dome rotation system described herein permits the automatic 
operation of the telescope observatory dome as the telescope is directed 
to different objects, or while it tracks one object as the earth rotates. 
The invention does not use complex computer control, but instead, relies 
on infrared sensors in connection with the telescope field and as the 
sensors detect the appearance of an edge (of the dome) in front of the 
telescope they, in turn, operate relays in connection with the operation 
of the dome in order to recenter the dome slot in front of the telescope. 
SUMMARY OF THE INVENTION 
The invention is a system for controlling the operation of a dome in 
connection with a telescope in order to maintain the slot of the dome in 
alignment with the telescope at all times so that stars may be viewed 
continuously. The system eliminates or minimizes the need for the user 
having to manually control the operation, usually rotation, of the dome. 
Preferably four infrared sensors and transmitters are mounted along the 
circumference of the telescope in order to send signals to a controller 
when the edge of the dome is detected which occurs when the signal is 
reflected back to the sensor. Each of the sensors should be 90.degree. in 
relation to each other. Each of the detectors is in connection with a 
controller. The controller is in connection with the movement system of 
the dome and sends signals to the movement system that rotate the dome 
until the sensors determine that the dome slot is aligned with the 
telescope. 
If the telescope is on an altazimuth mounting the telescope most move in 
both the altitude (up/down) and azimuth (horizontal/circle) to follow the 
star. If the telescope is on an equatorial mounting, the telescope need 
only be rotated around a single polar axis to follow the star. A telescope 
on an equatorial mounting will rotate relative to the earth and to the 
dome slot as it follows the star. The controller has a means for 
determining the down direction as the equatorial telescope rotates on its 
axis while following the stars, thus enabling the controller to determine 
which sensors correspond to the left and right slot edges. There are also 
verification systems in the sensors and the controller that provide that 
the reflected signal must be detected for a certain time period and that 
the clear signal must be detected for a certain time period before a 
signal is sent to the controller. 
It is an object of the invention to control the operation of a dome having 
a slot that is in connection with a telescope in order to maintain the 
slot in constant alignment with the telescope throughout the viewing 
period. 
It is an objective of the invention to provide the advantages of automated 
dome operation in connection with a telescope in a self-contained system. 
It is another objective to provide a telescopic dome rotation system that 
can be installed on any dome having electric rotation in order to automate 
the dome rotation process. 
Another objective is to use infra-red sensors in a dome control system in 
order to eliminate or minimize interference with the astronomical 
instruments as may arise from alternative dome control systems. 
Another objective is to provide an automatic dome movement system in order 
to maintain the slot of such dome in alignment with the telescope even if 
the telescope slews. 
Other objectives will be seen by those skilled in the art once the 
invention is shown and described.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows the overall setup of the typical installation. The controller 
is mounted on the telescope tube so that a built-in artificial horizon 
device within the controller can sense the orientation of the telescope 
relative to the earth. Sensor pods are mounted at the outward end of the 
telescope tube at 90 degree intervals around the telescope tube and are 
connected in pairs to the controller. The output of the controller drives 
a relay box or other device that controls the movement of the dome's 
electric drive motors. It is preferred that the controller and sensor pods 
receive their operating power from the relay box and dome drive power 
supply. 
The dome rotation system is shown in FIG. 1. There are four sensor pods on 
the telescope each having an infrared (IR) transmitter and a receiver in 
connection therewith. The sensor pods should be mounted around the outside 
circumference or the outer surface of the housing the telescope as shown. 
Thus, when the telescope is seen from the front one sensor pod will be at 
the top of the housing (i.e. 12 O'Clock to the viewer), one at the bottom 
(6 O'Clock), one on the left and one on the right (3 O'Clock and 9 
O'Clock). The sensor pods are connected to one another in pairs so that 
those on the top and bottom should operate as one pair and those on the 
left and right should be connected to one another in order to operate as a 
second pair. 
It is helpful to think of the telescope as having a housing that is of a 
tubular construction and having a viewing line or axis that defines the 
line along which the light from the heavens comes into the telescope. The 
construction of the housing of the telescope defines a tube that runs 
parallel to this line, and the sensor pods should be mounted on the outer 
surface of the tubular shaped housing of the telescope. 
FIG. 2 shows a block diagram of the controller-related components. The 
controller contains an artificial horizon, and an oscillator and a 
pre-programmed microcomputer that processes signals sent by the sensors 
indicating that the interior wall of the dome is in front of that 
particular sensor pod. The controller sends output signals to the dome 
motor control relays to control the movement of the dome. The controller 
also contains small indicator lights to show the operation. 
The controller section of the system is preferably mounted at or near the 
top of the telescope and controls the operation of the working parts of 
the dome by sending signals to the relay box shown in FIG. 1 in order to 
rotate the dome in response to signals (indicating the presence or absence 
of IR) sent to the controller by the sensor pods. The controller has a 
built in artificial horizon that determines which of the sensor pods is on 
the top of the scope and therefore which of the sensor pods is at the left 
and which is at the right. The controller will then use a logic system in 
connection therewith to select which of the pods corresponds to the left 
and right sides of the shutter opening and can then determine which 
direction to rotate the dome in order to maintain the slot in alignment. 
The system herein described can be used on telescopes equipped with either 
altazimuth mounts (e.g. Dobsonians) or on equatorial mounts. In an 
altazimuth installation, only two infra-red sensor pods are needed to 
detect the left and right edges of the dome slit using a sensor pod on 
opposite sides of the telescope (each sensor pod combines both a 
transmitter and receiver). However, a telescope on an equatorial mount 
will rotate once each day, relative to the earth surface, as it follows 
the sky. Thus, after tracking an object for six hours (or moving to an 
object six hour angles away) the telescope will have rotated 90 degrees. A 
sensor pod on the telescope that was properly aimed at the right side of 
the slit, will now sense the top or bottom of the slit, thus giving 
incorrect guidance to the observatory drive motors. To correct for this 
effect, the astronomer can manually change the sensor pod orientation on 
the scope (e.g., move them to the correct left/right position on the scope 
tube). Of course, this requirement for manual adjustment reduces the 
degree of automation available. 
However, using the four infrared sensor pods located at 90 degrees around 
the telescope and the information from the artificial horizon, the 
controller uses an internal logic table to detect the sensor pod 
corresponding to the left and right directions and the proper direction to 
turn the dome when a particular sensor pod is activated. 
The artificial horizon may be for example, a four pole mercury switch. 
Because the switch is attached to the controller and telescope, it will 
rotate as the telescope is rotated. The mercury switch will output voltage 
onto the lowest one or two of the four switch poles, thus indicating the 
orientation of the sensor pods i.e. which pod is on the bottom and hence 
which is on the top, which is the left, which is the right. 
The controller preferably has an internal memory which will keep track of 
that direction (clockwise or counterclockwise) the dome was previously 
moving in the event that the telescope moves all the way out of the slot. 
In that event, both left and right sensor pods will presumably send a 
signal to the controller, the controller in turn will send signals to the 
control system to continue turning the dome until the slit is aligned with 
the telescope. At that time, the sensor pods will send signals to the 
controller to indicate that this condition has occurred, we refer to this 
as a "clear" signal for purposes of convenience. The controller may 
include an automatic timer that will limit its operation of the dome to a 
nominal 100 seconds to prevent unnecessary wear in the dome drive if the 
telescope should be stuck in a continuous slewing operation. 
Each telescope-mounted sensor pod has its own built-in transmitter and 
receiver for infrared radiation. Both the transmitter and the receiver 
should have a lens. That lens on the transmitter can focus the IR beam and 
that on the receiver can increase the sensitivity of the receiver to the 
reflected IR beam. IR may be transmitted into a small spot, preferably 
about 1 inch at four feet, to minimize scattered infrared. When the dome 
slot is in front of the telescope, infrared is projected out the slot. No 
infrared is reflected back except when the slot edge moves into the 
infrared sensor field of view. The sensor pods will detect the slot edges 
of most domes at a distance of about 7-10 feet. Because the sensor pods 
should be located on the end of the telescope, domes of most any size can 
be controlled with this system. No special treatment of the dome edges is 
needed. As noted, the sensor pods respond to most materials in the 7-10 
foot range, and adjustment is normally not needed. Sensor sensitivity may 
be adjusted by the user by changing the power level for the IR 
transmitter. Sensor pods may be focused in order that lower power levels 
of radiation may be used. 
Although constructed together as a unit, each pod component is optically 
isolated from the other. The transmitter is an infrared emitting diode 
with a lens to focus the IR beam. The receiver component of the pod 
consists of a lens which focuses the reflected IR onto a modular IR 
detector. It is preferred that the detector respond to IR that is primary 
modulated at approximately 32 kHz, with a second low frequency modulation 
of about 700 Hz superimposed. Because of the detector characteristics, the 
controller includes a special oscillator and amplifier that produces 32 
kHz, and which is in turn shut off and on at about 700 Hz by the 
microcomputer. The result is that 32 kHz IR is emitted in bursts lasting 
about 700 us. 
It may be important to reduce the power levels of IR used in order to 
minimize the chances of reflected IR interfering with the telescope 
observation due to the fact that some IR may be reflected by the dome in 
the direction of the telescope objective area. Focusing, increasing 
sensitivity levels and using doubly modulated IR radiation may all 
contribute to decreasing power levels of IR. Doubly modulated IR (using 
frequency and/or amplitude modulation of the IR signal) allows the sensor 
pod to receive lower levels of IR. 
It is preferred that the IR beam used be a relatively small focused beam. 
If the beam is too small local reflection variations on the inner dome 
surface may cause the reflected IR not to reach the detector. Commonly, a 
too large beam reduces sensitivity in detecting the slot edge. The same 
would be preferred when other types of electromagnetic radiation sensors 
are used. The use of doubly modulated infrared light allows a high 
sensitivity without using high power levels. 
The relay box uses the signals from the system controller to control the 
dome drive motors to turn the dome clockwise or counterclockwise. 
The system automatically turns the observatory dome to keep the dome 
opening (slot) in front of the telescope while the user moves the 
telescope (by hand or automatic control). This avoids the need for manual 
operation of the dome, and is useful for long time exposures, for remote 
control of the telescope, or for quick viewing different parts of the sky. 
As the telescope moves so that the slot edge interrupts and reflects a 
portion of the transmitted IR, the modular detector begins to send a 
signal to the signal input of the microcomputer. As shown in FIG. 3, the 
microcomputer applies discrimination logic to determine whether the signal 
is to be considered a valid slot edge detection. For example, in the 
present embodiment, the logic requires that the signal be present for at 
least two seconds before being considered a valid slot edge detection 
(this discriminates against birds outside the slot). 
The controller then determines what the location of the sensor pod was that 
sent the signal i.e. whether this was the left, right, top or bottom 
sensor. The controller can do this by means of an artificial horizon 
previously described. With this information, the preprogrammed 
microcomputer then determines which way to move the dome in order to move 
the slot edge away from the IR beam. 
Once the logic decides on the proper direction to turn the dome, i.e., 
clockwise or counterclockwise, the microcomputer activates the proper 
output, sending a control signal to the relay control device that controls 
the operation of the dome. 
As the dome turns, the slot edge will move away from the IR beam, thus 
decreasing the reflected IR and reducing the detected signal. The 
discriminator applies logic tests to determine when there is a valid "slot 
edge gone" detection, for example, by requiring the signal to drop to zero 
for at least one second (to guard against short signal dropouts from any 
source, including variations in the reflectivity of the internal dome 
materials). Once a valid detection is made that the slot edge is no longer 
in the IR beam, the logic then continues to operate the dome for a 
"coasting" period. This period is selectable by the user to so that the 
dome will rotate the slot opening to a position centered in front of the 
telescope. 
As the dome is turning, the controller also keeps count of how long the 
dome has been turning. If the dome has turned continuously for more than 
100 seconds, the logic shuts down the dome rotation. This assures that the 
dome does not continue to operate indefinitely if some failure should 
occur in the system. This timeout feature resets by removal and 
reallocation of power to the system, or if the valid detection of "slot 
edge gone" is made. 
An important feature of the system logic in the controller is that the 
detectors will sense not only the slot edge, but in fact detect any 
portion of the inside surface of the dome. Thus, if the telescope slews 
faster than the dome turns, the logic in the controller will keep a record 
of which direction to continue turning until the slot opening rotates into 
alignment with the sensors. In addition, if the system (controller and 
sensors) is first turned on with the telescope and pods facing an internal 
surface of the dome, i.e., away from the slot opening, the system will 
automatically begin turning the dome until it "finds" the slot (or until 
the timeout is complete). 
The system may also include a handheld control that overrides the operating 
system in order to allow for manual control of the dome. The connection of 
the controller with the dome control systems may be by various means 
including direct wire connection, electromagnetic radiation, light, or 
ultrasonic signaling. Any state of the art system may be used to power the 
IR transmitters/receivers as well as the controller. 
The use of infrared energy with the sensors is believed to be the preferred 
method of detecting the dome and the slot; however, other types of 
electromagnetic radiation may be used without varying from the spirit of 
the invention. Such light emitters may include: visual light emitters, 
lasers, etc. Other energy systems that utilize focused beams of energy may 
be used, such as units that send and/or receive ultrasonic signals. 
Alternative detection systems also are feasible, in which different 
modulation and or phase sensitive detection is used. Such alternative 
systems may offer some advantages (e.g., of increased sensitivity and 
lower IR power use). The logic component in the controller may be any 
state of the art means. It is believed that a microcomputer may be the 
preferred logic component but other systems such as those that are hard 
wired may be used without varying from the spirit of the invention. 
The present system uses four transmitter-receiver pods at the 90 degree 
points of the telescope tube to provide for tube rotation of an equally 
mounted telescope. Alternative arrangements are feasible. These include 
use of a single pair of sensors (pods) that may be rotated, either 
manually or automatically, in order to maintain proper left-right 
orientation. Other methods may be used for moving the 
transmission-reception sensors around the telescope tube.