boettche@gumby.cs.wisc.edu (Michael Boettcher) (12/07/88)
In the past I have contemplated building a laser deflection/show system. I would consiste of four electro-magnets(like the speaker coils), but with the same polarity pointing towards the center. A bar magnet, or another electro-magnet is mounted on a pivit, with a mirror on the opposite end. The polarity of the magnet end within the fields of the four outer magnets would be the same. The inner magnet, connector, and mirror would all be very low mass, for low inertia. The basic idea is that the four outer magnets would repel the inner magnet. This would force it into the center. For control, you would decrease the field of one of the magnets. This would force the inner magnet in that direction. Besides the problem of vibration senitivity for the overall system, what kind of problems would there be for a system of this type. I was wondering if the inductance of the outer magnets would prevent a reasonable response rate. Before responding with information that a > $500 part has more sensitivity, realise that this is a $35 system, including scavanged electronics, and is intended as a hobby device. Thanks in advance for your input. ******************************************************************************* Michael Boettcher boettche@gumby.cs.wisc.edu Student, Univ. of Wisconsin 107 N. Randall Apt. I Applied Math, Engr. and Physics Madison, WI 53715 *******************************************************************************
abali@phao.eng.ohio-state.edu (Bulent Abali) (12/07/88)
In article <2110@puff.cs.wisc.edu> boettche@gumby.cs.wisc.edu (Michael Boettcher) writes: >A bar magnet, or another electro-magnet is mounted on a pivot, with a >mirror on the opposite end. The polarity of the magnet end within the >fields of the four outer magnets would be the same. The inner magnet, >connector, and mirror would all be very low mass, for low inertia. >Michael Boettcher boettche@gumby.cs.wisc.edu Mechanical control of the mirror as described above can be difficult. Following is what I would try: reflected beam . ---------- . / (mirror) I . / Laser . . . beam . . . . . ..x I / ---------- / Mirror is rotating freely at very high speed, around a shaft centered at x. Any speed above 1800 rpm (30 revolutions/sec) should be adequate. We can track the position of the mirror by an optocoupler and a circular grid attached to the shaft. Laser is off most of the time. Whenever mirror comes to the desired angle, we pulse the laser on. Since mirror is revolving at very high speed, the pulsed beam appears continously on to the eye. Advantage of this method: All electronical; position of the mirror is not controlled mechanically. Mirror can rotate at any speed and no calibration is necessary. Disadvantages: 1)Angle of the beam can be changed only in a 2-D plane. 2) Can you turn the laser on-off in the desired interval? -=- Bulent Abali Ohio State Univ., Dept.of Electrical Eng. 2015 Neil Av. Columbus, Ohio 43210 abali@baloo.eng.ohio-state.edu
jbn@glacier.STANFORD.EDU (John B. Nagle) (12/07/88)
The low rent approach to this problem is to glue a mirror to the
cone of an old loudspeaker. You can produce interesting but not meaningful
patterns in this way. A setup with two mirrors, one for X and one for Y,
allows positioning. Connection to a pair of D/As with DC-coupled power amps
provides computer control, or connection to an audio system provides
decorative patterns. Don't expect much precision.
The high rent approach is feedback-controlled mirror galvanometers
from General Scanning Corporation. These have a mirror, a galvanometer
movement, and a variable capacitor for position feedback. This is how
the laser-show people do it.
John Nagle