AUTOMATIC CONTROL SCHEME FOR MOVING A POINT COLLECTOR ALONG THREE MUTUALLY PERPENDICULAR AXES

Yu. I. Terent'ev

(Presented by the seminar of the VTE sector of the YaPhA Research Institute)

The article describes the operation of a scheme for automatic control of the movement of a point collector along three mutually perpendicular axes.

The scheme is intended to provide the possibility of indicating the distribution of the average current density of an electron beam in the volume under investigation and of recording the information obtained.

One of the methods for studying electron beams may be the measurement of the average current density at many points of the investigated volume by means of a point collector.

In order to reduce the time and improve the convenience of the investigation, we have developed the scheme shown in Fig. 1 for automatic control of a device that moves a point collector along three mutually perpendicular axes: the horizontal axis—\(x\), the vertical axis—\(y\), and the beam axis—\(z\). DC micromotors of type SL-221A are used to drive the device. The scheme is built on relays of types MKU-48 and RP-5, with the use of D701 limit switches and time delays. The limit switches are located along the corresponding axes (\(\mathrm{KV}_{1,2}\)—along the \(x\) axis, \(\mathrm{KV}_{3,4}\)—along the \(y\) axis, \(\mathrm{KV}_{5,6}\)—along the \(z\) axis) outside the investigated volume and are actuated by the action of the collector emitters, which operate synchronously with it.

Let us consider the operation of the scheme. Initially the collector is located at point \(I\) of the first investigated cross section of the electron beam (Fig. 2). We switch on toggle switches \(\mathrm{Tb}_1, \mathrm{Tb}_2, \mathrm{Tb}_3, \mathrm{Tb}_4\) and press the start button, which has normally open contacts \(n_1\) and \(n_2\). Relay \(P_1\) then operates and self-locks through normally open contacts (n.o.) \(1P_1\); the (n.o.) contacts \(2P_1\) and \(3P_1\) close, and the normally closed (n.c.) contacts \(4P_1, 2P_1\), and \(3P_1\) in the circuit of motor \(z\) open (moving the carriage together with the mechanism mounted on it for moving the collector along axes \(x\) and \(y\), and with the collector itself along the beam axis)—the motor is ready for operation. As a result of the shunting by contacts \(P_1\) of potentiometer \(R_1\), capacitor \(C_1\) charges to the nominal voltage during the time the button is pressed, which causes the polarized relay \(1\mathrm{RP}\)-5 to operate, and consequently relay \(B_2\) as well; the latter closes the n.o. contacts \(1B_2\) in the circuit of motor \(y\) and opens the n.c. contacts in the circuit of motor \(x\). Motor \(y\) starts, moving the collector downward. At the same time the (n.o.) contacts \(2B_2\) and \(3B_2\) close in the circuits of relays \(B_1\) and \(H_2\), but only relay \(B_1\) operates and self-locks, since the circuit of relay \(H_1\) is opened by contact \(\mathrm{KV}_1\) of the limit switch.

Fig. 1. Automatic control circuit for moving a point collector along three mutually perpendicular axes.

After capacitor \(C_1\) has discharged, relays 1RP-5 and \(B_2\) are de-energized; at the same time the n.c. contact \(1B_2\) closes—the \(x\) motor begins to operate, moving the collector along the horizontal line of the section, while the \(y\) motor stops. At the end of the line, limit switch \(KB_2\) operates, opening the n.c. contacts \(KB_2\) in the circuit of relay \(B_1\) and closing the n.o. contacts \(1KB_2\) in the circuit of relay 1RP-5. The \(x\) motor is then stopped and the \(y\) motor begins to operate after relays 1RP-5 and \(B_2\) operate, moving the collector downward to the next line, after which the working process proceeds in an analogous sequence.

Fig. 2. Trajectory of the collector motion in the investigated cross section of the electron beam

The distance between lines is set by changing the discharge duration of capacitor \(C_1\) by means of potentiometer \(R_1\).

At the end of the collector’s downward travel, limit switch \(KB_3\) operates and closes its n.o. contact \(KB_3\) in the circuit of polarized relay 2RP-5. As a result relay \(B_3\) operates and switches on relay \(P_2\); the latter reverses the \(y\) motor, opens n.c. contact \(2B_3\), thereby preventing motion of the collector relative to the carriage during motion of the carriage to a new position, and closes n.o. contacts \(1B_3\) and \(4B_3\) in the circuit of the \(z\) motor—the carriage begins to move along the beam axis by a distance determined by the discharge duration of capacitor \(C_2\).

After relay \(B_3\) is disconnected, relay \(B_2\) operates—the probing of a new beam section begins, but now in the reverse sequence, since the \(y\) motor has been reversed.

When the collector rises to the upper line, limit switch \(KB_4\) operates, closing its n.o. contacts in the circuit of relay 2RP-5 and breaking the circuit of relay \(P_2\). The \(y\) motor is switched for moving the collector downward, and the carriage again moves along the beam axis to the next position.

When, after a number of cycles, the carriage has traversed the entire region under investigation, limit switch \(KB_5\) operates and switches off relay \(P_1\). The \(z\) motor is reversed and, owing to the closing of contacts \(3P_1\), immediately begins to rotate in the opposite direction, moving the carriage to the initial position.

During this time the collector cannot move relative to the carriage, since first capacitor \(C_1\) is shunted by n.o. contacts \(KB_5\); when they open, the capacitor will continue to discharge through the winding of relay 1RP-5 with a current insufficient for its operation.

When the carriage returns to the initial position, limit switch \(KB_6\), by its n.o. contacts \(KB_6\), switches on signal lamp \(L_2\) and de-energizes the \(z\) motor.

The “emergency return” button permits the carriage to be returned to the initial position at any time.

For repeated investigation of one section, switch \(Tb_3\) should be switched off.

Owing to the presence of n.o. contacts \(4H_1\) and \(4B_1\) in the circuit connecting the collector with the recording device of the self-recorder, the signal is fed to the self-recorder only during the period of horizontal motion of the collector in the investigated section.

The circuit has been tested and operates reliably.