Sapphire Belt Puller
I just finished up another crystal puller, this one using belts to grip the
sapphire optical fiber instead of rollers. It appears to be the best one yet for
smoothness and stability. We need to be able to get speeds in the 1/2 inch per
hour range.
I'm using a small Maxon motor with built-in 100:1 gearbox, a 500 line encoder on
the high speed shaft followed by a right angle 3:1 gear set and then into a
15.7:1 gearbox driving the gear coupled drive rollers. If you are following the
math, that is a 4710:1 reduction.
The main difference in this puller vs. the other units I've built is that I'm
not using the standard tachometer feedback servo controller. I'm using a servo
control from Gecko that uses the encoder signal for feedback control. This
controller is amazing. It's about 2.5 inches square by 3/4 inch thick. It can
drive 20 amps with an 80 volt supply. The cost of this is only $114 in single
unit quantities.
I'm driving the step pulse input with a CMOS (4046) voltage controlled
oscillator as the reference source. The control compares that to the encoder
output from the motor to keep the speed constant. A lot of people are making
hobby CNC units from their mill/drills and lathes using this control.
I have another controller from a few years ago with similar capabilities that is
in a box measuring 6 X 6 X 8 inches, built-in fan, three circuit boards and
massive heat sinks. I don't know what it cost, but it must have been close to
four figures. The biggest reason for the reduction is size is the switching
devices in the output bridge. The switching frequency is 25 Khz. There is almost
no loss of power in the transistors as they are either fully on or completely
off. The transition time between the two states is very short.
Did I say I'm impressed?
Earle Rich
Mont Vernon, NH
sapphire optical fiber instead of rollers. It appears to be the best one yet for
smoothness and stability. We need to be able to get speeds in the 1/2 inch per
hour range.
I'm using a small Maxon motor with built-in 100:1 gearbox, a 500 line encoder on
the high speed shaft followed by a right angle 3:1 gear set and then into a
15.7:1 gearbox driving the gear coupled drive rollers. If you are following the
math, that is a 4710:1 reduction.
The main difference in this puller vs. the other units I've built is that I'm
not using the standard tachometer feedback servo controller. I'm using a servo
control from Gecko that uses the encoder signal for feedback control. This
controller is amazing. It's about 2.5 inches square by 3/4 inch thick. It can
drive 20 amps with an 80 volt supply. The cost of this is only $114 in single
unit quantities.
I'm driving the step pulse input with a CMOS (4046) voltage controlled
oscillator as the reference source. The control compares that to the encoder
output from the motor to keep the speed constant. A lot of people are making
hobby CNC units from their mill/drills and lathes using this control.
I have another controller from a few years ago with similar capabilities that is
in a box measuring 6 X 6 X 8 inches, built-in fan, three circuit boards and
massive heat sinks. I don't know what it cost, but it must have been close to
four figures. The biggest reason for the reduction is size is the switching
devices in the output bridge. The switching frequency is 25 Khz. There is almost
no loss of power in the transistors as they are either fully on or completely
off. The transition time between the two states is very short.
Did I say I'm impressed?
Earle Rich
Mont Vernon, NH