2-axis angular

[mattinjersey]

I am trying to construct a 2-axis angular mount that can rapidly point to all angles. The application is for the secondary mirror of a Cassegrain telescope. My idea is to have a base spinning. And then a tipping platform on the spinning base. See diagram below. If the base is spinning, then if the platform is held at a certain angle, it will sweep out a circular angle as is rotates. Both the tipping platform and the rotating base to be computer controlled. But I really have no idea on what components I could use. Any suggestions ? - - - Tipping platform - - ------------ rotating base x x x x

[MikeS81]

Hi mattinjer…,

did you already define on which platform you want to work (PXI, PC, ...)? There are lots of PXI cards to control a motor. Do you want to use stepping motors?

Mike

[mattinjersey]

Hi Mike,

I am open to any board. I know that I can control 1 stepper motor, no problem.

But I am puzzled on how to build the mechanical/electronic design.

To go back to my proposed design, the stepper motor rotates a shaft that is connected to a platform. So the whole platform is spinning. Then I would like to mount another motor on this spinning platform. Not sure how I might control/power this 2nd motor.

Thanks Matt

[johnsold]

Matt,

Does your rotating platform need to provide continuous rotation or can it stop after, say 370 degrees, and reverse? If the total rotation is limited, then a cable is the easiest and most reliable way to power the tipping. If unlimited rotation is required, the standard way is to use slip rings. It may also be feasible to use inductive coupling for power and a radio link for communication and control. Does the moving platform hold only the mirror or does it carry instrumentation? What kinds of sensors are to be used for position and angle feedback to the controller or is open loop control of the stepper motor good enough? How do you find the reference position if open loop control is to be used?

Lynn

[mattinjersey]

Hi Lynn,

I am leaning towards continuous rotation because I would like to get very high speed. For example I would like to have a complete rotation in 0.1second. If we stop and start I think the speed will be drastically reduced. But if you think we could get such a fast rotation with a limited rotation, I would be very interested to learn that.

So that may lead us to slip rings to power the device, and then wireless comm to control the device, as you suggest.

I think open loop control of the stepper would suffice. I need 0.2degree resolution. If the steps don't slip, I think it would suffice.

The moving platform hold only the mirror.

As far as your question about the reference position, maybe I could start at 0 position for each run ?

Thanks Matt

[johnsold]

Matt,

Standard stepper motors go to steps of 1.8 or 0.9 degrees. Controllers offering "microstepping" can produce finer resolution, IF everything works perfectly. Under these conditions stepper motors act more like the synchronous motors they are and slippage becomes more of an issue.

With the speed and resolution you want, I think you should talk to someone experienced in positioning systems to make sure you can get what you need.

Lynn