macro rail motor

For an automated stack focusing shot sequence:

Purpose: Even if a microscope’s statif allows to set the focusing accurately, in order to sequence the views at different focusing depths, this becomes much more difficult in macro mode, with high magnifications.

first step:

Find a stepper motor able to drive correctly the advance button. One knob’s revolution corresponds to a 25 mm advance. With a 200 steps motor (a quite standard one), the advance is going to be 1.25 tenth per step. Let’s evaluate now the motor torque when tightening a small aluminium ruler instead of a knob, in order to realize a small pair of scales. A 110 gr weight (my keys bunch) moves along the ruler, till it makes the rail start..in my case: 9 cm. So the necessary torque is calculated as: 0.09 m * 0,11 kg * 9,82 (acceleration)....roughly 0.1 N.m. A 0.6 N.m stepper motor (200 steps) will be convenient. Another consideration is to be taken into account for the motor’s choice: the power interface. In my situation, I’ve chosen a "on the shelf" control unit kit and I’ve adapted it. This kind of unit obliges to choose an unipolar type motor.

Second step:

Mount the motor on the rail. Two aluminium bars are shaped in order to link the part under the rail standing, and the axle side of the motor. The clutch is realized on the motor side with a potentiometer-type knob, on which two cross-shaped grooves are made to insert an aluminium crossbar.... Same operation on the rail control knob...then the clutch can be done, it works, and is few destructive for the rail.

Third step:

pilot the motor control unit: on/off, direction and speed. On the STEP EASY unit, this is realized with reversing knobs, and a potentiometer for the speed. I have added another switchable potentiometer in order to allow two speeds, one for the fore and back focusing, the other to permit the advance during the shots. All these actions will be made with help of automate-driven relays.

Fourth step: the automate.

Working from a PIC BASIC PBM-R1 comfile on I/O CELL card. It receives the commands of the foreward, backward, shot activation control unit, and sends the motor impulsions consequently, as well as the camera starting

Operation:

 set the advance knob to obtain a number of steps per second, time imposed by the flash recycling, for instance : two steps per a two-tenth advance between two pictures.
 frame the subject and focus on the sharp foregroung, with the two focusing buttons.
 activate the shot while maintaining the red button, as long as shots are wanted.

Partial conclusion:

still to be done: test and modify the standing, on order to gain mobility.