ELECTRON-ION PULSE SERVO FEED OF GROOVE-GRINDING MACHINES

V. A. BEINAROVICH, A. I. ZAITSEV

The groove-grinding machines currently being produced are equipped with unregulated drives with asynchronous motors. An increase in productivity and an improvement in the quality of machining of parts can be achieved through the use, on the machines produced, of servo drives for transverse feed, as well as systems for maintaining constancy of the linear grinding speed [1, 2, 3, 4].

At the EPP Department of Tomsk Polytechnic Institute, a system of electron-ion pulse servo feed has been developed for groove-grinding machines of the LZ-5M type.

Servo feeds regulate either according to the speed of the actual feed, that is, according to the speed of allowance removal [1, 4], or according to the grinding power [3]. In the version of the system presented here, regulation is carried out according to the speed of the actual feed, since on LZ-5 machines only self-sharpening grinding wheels are used and, in this case, the speed of the actual feed determines all the principal indices of the grinding process: burn depth, surface finish, machining cost, grinding-wheel wear, and others [1, 2].

Fig. 1.

In structure (Fig. 1), the developed servo feed represents a closed-loop relay-action ACS with rigid negative ...

feedbacks for the workpiece allowance, the actual-feed speed, and the motor-feed speed.

The principle of operation of the system is as follows. The magnitude of the workpiece allowance \(S\) is linearly converted by inductive sensor 1 into a voltage \(U_s\), which is fed to programming unit 2 and differentiating stage 3. The voltage \(U_z\), proportional to the specified feed speed, and the voltage \(U_d\), proportional to the actual-feed speed, are fed to comparison element 4. A voltage \(U_m\), proportional to the motor-feed speed, is also applied there. This connection ensures that low feed speeds are obtained at the end of grinding, when the value of \(U_d\) tends to zero. The deviation \(\Delta U\) is fed to relay element 5 and amplifier 6 and ensures operation of motor 7 at the speed required to obtain the specified actual-feed speed. When \(U_d + U_m < U_z\), motor 7 is switched on and produces the transverse feed; when \(U_d + U_m \geq U_z\), the motor is de-energized.

The electrical circuit of the following feed is shown in Fig. 2. The amount of allowance is measured by an inductive sensor ID with a sensitivity of 80–100 V/mm. The sensor voltage, by means of the stabilitron D-810 \(D_1\) and limiting resistor \(R_4\), is shaped into positive pulses on \(R_6\), whose amplitude is proportional to the allowance in the range from 0 to 0.1 mm and is constant for \(S > 0.1\) mm; in this way programming of the specified actual-feed speed \(V_z\) as a function of the allowance \(S\) is accomplished (Fig. 3). A voltage proportional to the actual-feed speed is applied to \(R_8\), and to \(R_9, R_{10}\) the motor-feed voltage is applied. Both of these voltages have a polarity opposite to that of the programming pulses. After detection by diode \(D_2\), the mismatch-voltage pulses are fed to amplifier \(L_1\)—\(L_3\), into the grid circuit of thyratron T, “open” the thyratron, and the feed motor DP receives power and carries out the feed. The system is designed in such a way that, in the absence of actual feed, the motor-feed speed \(V_m\) exceeds the specified value by a factor of 2.3. Such forcing ensures that the specified actual feeds are obtained even when the softest grinding wheels are used. As soon as the magnitude of the actual feed reaches the specified value, diode \(D_2\) opens and shunts the amplifier input. As a result, thyratron T is blocked by the reference voltage \(U_0\).

The moment at which machining is completed is fixed by the zero indicator NI, in which a polarized relay RP-4 and amplifier PT on triode P-16 are used. The circuit responds to a change in the phase of the inductive-sensor voltage as it passes through the zero value.

The feed motor DP, type MI-12F with independent excitation, operates in a system with pulse speed control according to a nonreversing circuit. The use of a nonreversing circuit is possible owing to the high rigidity of the LZ-5 machine. Pulse speed control makes it possible to obtain a large control range (more than 60) with a simple contactless circuit. In the rapid approach and retraction modes, the motor is supplied with increased voltage, and thyratron T is used as an uncontrolled rectifier.

The value of the actual-feed speed is set by changing resistor \(R_{10}\).

Adjustment of the minimum feed speed at the moment the grinding process ends is carried out by means of resistor \(R_2\), by introducing an additional voltage that ensures obtaining the minimum transverse feed when the inductive-sensor voltage is equal to zero, since the zero indicator operates, as stated,

Fig. 2.

above, when the voltage of the inductive sensor passes through the zero value and the phase changes by 180°.

The tracking-feed system differs from earlier ones [4] by greater operating stability, elimination of the influence of the spread in the thyratron starting characteristic, absence of a modulator, simplification of the circuit, and increased reliability.

The developed system can also be used when it is necessary to regulate the feed rate as a function of grinding power. For this purpose, a DC voltage proportional to the grinding power should be applied, with the indicated polarity, to the resistance \(R_8\).

Tests of the tracking feed on an LZ-5M machine showed that it provides the specified technological grinding cycle (Fig. 3).

Fig. 3.

The grinding time is reduced on average by 27%, the surface finish is improved by one grade, burns are absent, and dimensional scatter is reduced by a factor of 3–4. The developed tracking-feed system has small overall dimensions, low weight, and low cost, and contains no scarce parts. The circuit parameters are not critical; adjustment is reduced to phasing the voltages by appropriately connecting the winding leads. Manufacture and servicing of the tracking feed do not require high qualifications. The system is made as a replaceable unit.

LITERATURE

1. E. S. Zheleznov. Electric tracking feed for grinding grooves of bearing rings. Technology of the Bearing Industry, VNIPP, No. 10, 1956.

2. Kh. Kh. Batalov. Experimental study of spherical grinding of bearing rings by the rolling method. Machines and Tooling, No. 1, 1956.

3. A. A. Sirotin, V. A. Eliseev. A new electric drive for grinding machines operating according to a specified cycle with maintenance of constant grinding power and speed. Automation of Mechanical-Engineering Processes, vol. 1, 1962.

4. V. A. Beinarovich, A. I. Zaitsev. Automation of groove-grinding machines. Proceedings of Higher Educational Institutions. Mechanical Engineering, No. 3, 1962.

Received by the editors in June 1962.