Mechanical Structure „Pi of the Mechanical Structure „Pi of the Sky” roboticSky” robotic telescopetelescope

mgr inż. Robert Pietrzakmgr inż. Robert Pietrzak

mgr inż. Piotr Wawermgr inż. Piotr Wawer

mgr inż. Roman Wawrzaszekmgr inż. Roman Wawrzaszek

21.05 – 27.05 200721.05 – 27.05 2007

OutlineOutline

Robotic telescope concept Principle of operation Mechanical design details

− Drive mechanical concept− Stepped motor coupling− DEEP / WIDE driver

Final device

Robotic telescope conceptconceptTwo versions of robotic-telescopes with four camerasTwo versions of robotic-telescopes with four cameras

The construction to The construction to the right is based on the right is based on the prototype the prototype designed by G. designed by G. Pojmański and Pojmański and installed in Las installed in Las Campanas Campanas Observatory in Chile. Observatory in Chile. In the left side there In the left side there is new version of this is new version of this construction.construction.

Robotic telescope conceptRobotic telescope concept

1. 1. RReduce the size of the RA educe the size of the RA wheelwheel

2. 2. TThe mechanism for he mechanism for deflecting thedeflecting the camerascameras

3. 3. To mTo move the cameras ove the cameras outside of the wheeloutside of the wheel

Differences between two conceptionsDifferences between two conceptions

Principle of operationPrinciple of operation The construction is based on a classical The construction is based on a classical

two axis parallactic mount concept. two axis parallactic mount concept. The first, called RA (for righ ascention) is The first, called RA (for righ ascention) is

parallel the Earth axis, while the second parallel the Earth axis, while the second one, called Dec is perpendicular to the one, called Dec is perpendicular to the first one. These two axis enable to point first one. These two axis enable to point the cameras to any point of the celestial the cameras to any point of the celestial sphere, assuming thesphere, assuming the overall overall construction is properly aligned with the construction is properly aligned with the Earth axis.Earth axis.

There are two working modesThere are two working modes:: a a common FoV and adjacent FoVs which common FoV and adjacent FoVs which are provided by the mechanism of the are provided by the mechanism of the deflecting cameras. Each of the deflecting cameras. Each of the cameras has two possible positions – cameras has two possible positions – one with the camera axis parallel to the one with the camera axis parallel to the RA axis, the second one deflected by RA axis, the second one deflected by 15º along the diagonal of the CCD chip.15º along the diagonal of the CCD chip.

Mechanical design detailsMechanical design details

The RA wheel is drive by The RA wheel is drive by friction gear. Stepper motor friction gear. Stepper motor with a step of 1.8° (200 with a step of 1.8° (200 steps for full rotation) are steps for full rotation) are used. Kinematics transfer for used. Kinematics transfer for the RA gear is equal the RA gear is equal 1142.851142.85. It is . It is 5.675.67 arcsec for arcsec for one step of the motor.one step of the motor. Pressure between the Pressure between the wheel and drive roll is wheel and drive roll is constant, given by constant, given by gravitation.gravitation.

Drive mechanical conceptDrive mechanical concept – RA – RA axisaxis

RA wheel

RA axis

Stepper motor

Harmonic gear

Mechanical design detailsMechanical design details

Ring of a wheel is made of Ring of a wheel is made of hardeninig steel.hardeninig steel. Wheel Wheel surface which contact with surface which contact with the drive roll has a barrel the drive roll has a barrel shape to improve the friction shape to improve the friction gear quality.gear quality.

Drive mechanical conceptDrive mechanical concept – RA – RA wheelwheel detailsdetails

Mechanical design detailsMechanical design details

In declination, the In declination, the kinematics transfer is kinematics transfer is equal equal 857.14857.14, , equivalent to equivalent to 7.567.56 arcsec for one step of arcsec for one step of the motor.the motor.Pressure between the Pressure between the wheel and drive roll is wheel and drive roll is control by the plane control by the plane spring.spring. Declination angle is Declination angle is changed between changed between ±±123123°.°.

Drive mechanical conceptDrive mechanical concept – DEC – DEC axisaxis

Mechanical design detailsMechanical design details

Stepper motor with a Stepper motor with a step of 1.8° (200 steps step of 1.8° (200 steps for full rotation) are used. for full rotation) are used.

Vibrations from the Vibrations from the stepper motor are stepper motor are insulated by the polymers insulated by the polymers coupling.coupling.

It’s consist with two It’s consist with two elements filled by elements filled by Solithane 113.Solithane 113.

Stepped motor couplingStepped motor coupling

Mechanical design detailsMechanical design details

DEEP/WIDE positions areDEEP/WIDE positions are realized realized by the screw propeller which is drive by the screw propeller which is drive by DC motor.by DC motor.

Change positions from one to other Change positions from one to other takes 54takes 54.2.2 s s..

DeepDeep / Wide D / Wide Driverive

Final deviceFinal device

The mount is equipped with end-switches used to limit the movement of the mount in a save range. Together with a “home” switch in the middle, they are also used for absolute position estimate. The automation consists of stepper motors steered by controllers from TRINAMIC company. To read the angle values, 13 bit multiturn Absolute Encoders are used. It has over 8192 counts per revolution. That gives a resolution of about 2.4 arcmin.

Final deviceFinal device

The cThe coonstruction is controlling by testing programnstruction is controlling by testing program

Thank you for your attentionThank you for your attention ! !