PC controlled Focuser

This is a PC controlled focuser based on Ethernet stepping motor controller. Here are, in a nutshell, the main features of this system :

- Two phases stepping motor, down to 1/128 micro stepping
- PC communication using Ethernet board (same as ethernaude)
- Dual stepping motor controller (MMT "Multiple Motor Telescope") that can handle up, to 4A per stepping phase : high torque allowing the drive of heavy focal plane instrumentation (CCD camera).
- Full remote software customizable speeds and rotation directions
- Embedded virtual encoders, 25600 steps per stepping motor rotation.
- Inductive proximity sensor to perform the reference or zero focus offset, allowing absolute positioning and pure digital focusing shifts.
- Backslash software compensation (if needed).

Have look here, another focuser applied to an INTES Mk707 Telescope

The overall system can be seen in this picture, a CCD camera has been mounted on top of the focuser (the black stuff underneath the CCD camera).

Below, the PRISM software panel, allowing accurate absolute and relative focusing

The Electronic board, the yellow cable is the ethernet cable. The top board is an Ethernet board (type Ethernaude board)

These pictures show the stepping motor driver board (MMT). The ethernet board has been removed, since this board is able to drive two stepping motors, I decided not to populate the parts needed for the second motor, because I simply don't need it. Nevertheless, this PCB is able to drive in parallel two stepping motor, the second one can be used for a filter wheel, for instance.

The mechanical interface made by VALMECA, as well as the focuser. The Sanyo Denki stepping motor is mounted on an aluminum arm, a "saw teeth" driving belt allows the main wheel of the eyepiece / camera CCD holder (i.e. the focuser indeed) to rotate.

The screw (bottom right of the image) and the two nuts, lying on the table, is the proximity inductive sensor allowing an accurate positioning reference.

Since one turn of the main focuser wheel shifts the CCD camera of 1mm, in this case the relative positioning accuracy is virtually 1/(200*128)= 0.000039 mm. A more realistic value of absolute positioning of couple of microns can be reached.