How Factory Production Is Being Made More and More Automatic by Amazingly Accurate Methods of Measurement and Control



YOUR life after the war is going to be affected by electronics in many ways. The great impact will come, not through any one spectacular development, but through the expanding uses of electronics in industry. Why? Because the production of countless necessities of life— houses, autos, machinery, tools, will be immeasurably speeded up and improved.

The extraordinary strides made by electronics in war production have pointed the way. We now know how to control manufacturing operations with superhuman accuracy, how to assemble materials with amazingly precise methods of welding, and how to run motors at infinitely varying speeds to suit each changing phase of machine operation. And we can do much of it automatically.

As Carl Dreher outlines the wonders of industrial electronics in this article, they give marvelous promise for the future. But they also present a great—perhaps an even greater—challenge because of the extent to which electronic controls may replace skilled workers.

THE variety of functions of which electronics is capable, in industrial applications alone, could not be described in anything short of an encyclopedia. All we can do here is to glance at a few things electronics can do better than they were done before, and others which, without electronics, could not be done at all. When, less than two centuries ago, James Watt began working on his steam engine, he was at first unable to obtain a round piston that would fit snugly inside a cylinder. With the machining methods then in use, there might be spaces of a quarter of an inch through which the steam could escape. Nowadays, machine parts are commonly made with a tolerance of less than a ten-thousandth of an inch. Length, thickness, speed, time, mass, illumination, chemical composition, electrical quantities—are all measured with an accuracy of only a few parts in a million, and usually you find electronic or semielectronic devices doing the measuring.

An example of a wholly electronic measuring instrument is the cathode-ray oscillograph. Called “the most versatile measuring instrument ever devised by science,” it has been used in industry for not much over 10 years. The operating principle of the cathode-ray tube is the deflection of an electron beam by electrodes in the neck of the tube, to which an unknown variable voltage is applied. Functioning as a weightless pointer, the beam traces a curve on a fluorescent screen, which shows how the voltage varies with time.

In industry, the cathode-ray oscillograph will reveal exactly what is happening inside a radio transmitter or receiver. It will draw a picture showing how lightning affects a transmission line, an alternator, or a circuit breaker. The magnitude and duration of welding currents, the behavior of electronic motor controls, and of every other electronic or electrical machine, can be studied in the utmost detail. By using some form of pickup to convert mechanical into electrical energy, the vibrations of machines, engines, musical instruments, and timepieces may be analyzed. Metals may be tested for composition and characteristics by observing their magnetic or electrical behavior when subjected to high-frequency fields.

When the middle-aged engineers of today were at college, the usual method of measuring the speed of a rotating machine was to stick a mechanical tachometer or revolution counter against the end of the shaft. In the case of a very small motor, the tachometer load might be enough to slow it down. With high-speed machines, the method was likely to be inaccurate because of slippage. By means of an electronic straboscope—a light flashing at a known frequency—the speed of a rotating object may be measured accurately without contact.

Electronic measurements may deal with quantities inappreciable except by almost incredibly sensitive instruments, or as great as the distance of a star from the earth. They may soar out into space—or burrow into the earth. In scientific exploration for oil, dynamite is exploded in a shot hole, setting up a small artificial earthquake. Suitably disposed pickups, designed to convert earth vibrations into electrical vibrations, respond to the reflections from the underlying rock strata. The outputs of the pickups are amplified electronically and recorded as seismograph traces, which permit mapping substrata as deep as 20,000 feet.

The new technique of resistance welding requires electronic control. The process consists in joining metal parts by pressing them together mechanically, sending an electric current through the joint, then shutting off the current and maintaining the pressure for another instant while the molten metal “freezes.” It sounds simple; the catch is that the number of amperes sent through the weld, and the length of time the current flows, must be precisely controlled. When a welding engineer specifies that a given number of amperes of 60-cycle current are to be sent through the metal for, say, a quarter of a second, he doesn’t mean 14 or 16 cycles, he means exactly 15 cycles. Any deviation may mean the difference between a perfect weld and a poor one. Some types of precision resistance welding are actually done in a fraction of a cycle, and it has to be the same fraction each time, in the same part of the cycle.

Welding even thin sheet steel calls for currents of several thousand amperes. For large parts, welding currents may be in the vicinity of 50,000 amperes. These currents are produced by a step-down transformer, but even the primary current of such a transformer will run to several thousand amperes. Making and breaking currents of this magnitude is a ticklish job, and it has to be done automatically hundreds of times a minute. About the only kind of switch that measures up to the job is a frictionless and inertialess device in which small amounts of power can control large amounts —in short, an electronic device.

Resistance welding with electronic control, applied on a commercial scale, is now well over 10 years old. The war, plus the inherent reliability, speed, and economy of this type of welding, has given it a powerful impetus. Already over 10 percent of the rivets used in airplane manufacture have been replaced by spot welds. Ultimately there may be a 100 percent change-over in this field. This is only one application of resistance welding; gasoline tanks, automotive parts, refrigerators, and vacuum tubes are others.

Induction heating, a comparatively new method of applying heat in industrial operations, has also contributed materially to war manufacturing, and promises to play a significant part in postwar electronics. By older methods, heat is caused to flow into the material from the outside, so that the surface gets hot first and may be overheated before the inside is even warm. With electronic methods, heat may be produced within the material, so that, if desired the whole mass can be kept at a uniform temperature throughout the process. Or, with equal ease, electronic heat may be applied selectively. By using a small radio-frequency coil, for instance, it is possible to harden the slotted end of a setscrew to a depth of 1/10 inch, leaving the rest of the screw soft so that it will make a gastight seal. Gears or crankshafts, for example, may be surface-hardened without causing internal brittleness. A smooth coating of tin only 30 millionths of an inch thick may be electroplated on sheet steel heated inductively to a temperature of 450 degrees F. Many similar applications will be found in which electronic heating results in a better product.

There are two general types of induction heating: electromagnetic and electrostatic. If the material is a good conductor, it may , be placed in or near a coil of wire in which alternating current is flowing. The electromagnetic lines of force cut the material, inducing eddy currents that release heat. In other words, we make the material to be heated the secondary of a transformer and the secondary is also the load. If the material is a poor conductor or an insulator, we place it in the electric field between two metal plates connected to a radio-frequency oscillator. The material then becomes the dielectric element of a condenser or capacitor, and is heated by dielectric losses.

Electrostatic heating requires high frequencies; its present band is 500 kilocycles to 50 megacycles. Up to about 12,000 cycles, alternating-current generators are the usual power source, but in the kilocycle and megacycle ranges, vacuum-tube oscillators and, to some extent, spark gaps are employed. The process is then truly electronic and the name radiothermics is sometimes applied to it. (P.S.M., May ’43, p. 56.)

A comparatively recent application of electrostatic heating is in the quick curing, or drying, of the glue and plastic adhesives in bonding plywood such as is used in airplane propellers. It is also important in the plastics industry. The preform, or piece to be molded, may be heated electronically so that when it reaches the molding press it is uniformly hot and plastic inside and opt. In the electronic “sewing machine,” thermoplastic sheeting, such as is used in raincoats and packaging, may be joined by application of heat to soften the material and form a seam under pressure. The material is fed through a pair of rollers connected to a radio-frequency generator. Since the rollers are merely terminals and do not get hot themselves, the material has no tendency to stick to them and is readily welded into an air-and watertight bond.

In the development of mercury-arc and other electronic rectifiers for large-scale conversion of AC into DC, we see one of those long-term swings in technological history that color the lives of millions. . Around 1880, Thomas A. Edison created the electric-power industry from the theoretical materials of Faraday and the other pioneers. DC was his baby and he could never see anything else. But for some decades thereafter, the development of AC technique, associated with Westinghouse, Stanley, Tesla, Steinmetz, and other great names, was the principal feature of electrical engineering. Although DC remained important in electric traction, in communication, on ships, and later for ignition and lighting in automobiles and airplanes, in this period it was definitely in second place.

Now we are witnessing a veritable renaissance of DC. One reason for this is the superiority of the DC motor where flexible speed control is needed. A much bigger influence, however, is the rise of the electrochemical industry, in which DC is needed for the electrolytic production of magnesium, aluminum, copper, and other light and heavy metals. Since power distribution remains an AC province, this calls for increasing numbers and higher powers of electronic rectifiers of the ignitron type. Rotary converters could be used, but rotating machinery has its disadvantages, especially at high voltages. Tubes are less liable to become damaged from overloads, and are better adapted to handle varying power requirements.

The availability of convenient and efficient rectifiers, in turn, encourages industrialists to use DC equipment for still other purposes. So DC and electronics, in partnership, are going places—and the technological irony of it is that all rectifiers derive originally from the “Edison effect” of electronic emission from lamp filaments, which dates back to 1883. AC won out over Edison, but now, to an increasing extent, we are converting AC back to DC, using another of his nuclear ideas.

Even in the field of long-distance power transmission, in which AC has reigned unchallenged for half a century, it may have to move over and make room for DC. Among other engineer-prophets, J. D. Ross, the public-power magnate of the Northwest, foresaw vast power transmissions over thousands, not hundreds, of miles—from generating sites near deposits of cheap coal to the great industrial centers. Ross talked of blocks of a million kilowatts to be transmitted from the lignite beds of the Northwest to Chicago and New York. But not by AC.

For one thing, the potentials required would be of a half million volts and up. With AC this would entail peak voltages 1.41 times as great, which at a given point would become impossible to handle. A DC voltage is always the same and, since it has no peak value, is less liable to trouble from corona and flash-back. DC is also free from inductive and capacitative losses.

Alternating current would remain in the picture for generation and voltage transformation, but once the voltage was stepped up, grid-controlled mercury-arc rectifiers or equivalent electronic means would convert it to DC for transmission. At the other end, the power would again be converted to AC, stepped down for local distribution, and consumed either as AC or, after another rectifier stage, as DC.

The first modern factories generated water and, later, steam power in large blocks and distributed it mechanically to the machines through a maze of ceiling drive shafts, pulleys, and belts in which the greater part of the power was lost. The only method of speed control the individual operator had was to change pulley ratios. He stopped his machine by letting the belt run free, or by means of a clutch. Individual electric-motor drive, which began to come into use in American factories in the late 1880′s, gave the operator much more accurate and flexible control. But it still involved human reactions and judgment, and it was necessarily discontinuous. Something happened and somebody did something and the machine responded, early or late, rightly or wrongly, depending on the skill of the operator and the inertia of the intervening mechanism.

Engineers and industrialists realized that the ideal method in mass production would be to let the material being worked make its own predetermined and continuous adjustments of the driving mechanism. This obviously required some form of feedback by which the material could talk back to the machine. An example is seen in Fig. 1 on page 131, where a loop in a sheet or wire strip that is being fabricated regulates, through mechanical or electrical linkage. the speed of the driving machine in proportion to the increasing diameter of the material as it winds up on a reel.

But what was the feedback linkage to be ? If, in order to control the power source, it had to handle considerable amounts of power itself, the inertia of the parts would slow down the response and make the mechanism less effective. Obviously, what was needed was an amplifier. The electronic engineers furnished the solution in the form of a system of vacuum tubes and associated circuits which, given a small stimulus, would react in a big way—silently, reliably, and in practically no time at all.

Fig. 2 shows one form of electronic motor control. A DC motor has its field and armature supplied from an AC source through an adjustable voltage rectifier using thyra-tron tubes. When the loop becomes too long, the reactor core enters the coil, altering the phase relations of the grid and plate voltages in the thyratron and causing the motor to speed up. A short loop withdraws the core and slows down the motor. Instead of a reactor, a photoelectric system may be employed, as in Fig. 3, where the loop varies the amount of light reaching the photocell and regulates the speed of the motor accordingly.

An outstanding advantage of this type of electronic motor control is that the tubes act as both rectifiers and regulators, making it possible to use DC motors on existing AC power lines. The AC motor is essentially a constant-speed device, since its speed bears a fixed relation to the frequency of the current. Manufacturing processes often require a variable-speed drive. The DC motor fills this requirement perfectly. It is possible not only to vary speed as required by the manufacturing process, but to control acceleration, deceleration, and even direction of rotation. The electronic control will start the motor, bring it up to a preset speed, change the speed, brake and stop the motor, then reverse it. All the operator has to do is put the material into the machine, press a button, and take the finished work out. In some cases, all he has to do is press the button.

Devices of this kind have been in use for about 10 years. So far, electronic motor control has been applied only to motors of relatively small horsepower, particularly in the machine-tool industry, but with larger tubes there is no reason why it cannot be used to control larger motors.

Electronic motor control belongs to a class of devices capable of doing something electronically that otherwise would have to be done—usually not so well—by human effort. The converse of this is when something is kept constant under changing conditions, like the output voltage of an alternator under varying load. The same thyratrons that vary motor speed can be used to vary the field excitation of the alternator, raising and lowering it in proportion to the shifting load more accurately than a human operator could do it, and keeping the AC line voltage constant to within a fraction of a volt.

Then there is a multitude of electronic detecting, counting, sorting, and inspecting devices. The inertia of electrons is negligible, and photoelectric relays are now made to operate reliably 1,000 times a minute. Some electronic counting systems will respond to half a million counts a minute. From counting it is only a step to sorting. If defective rivets have a different color from sound ones, the photocell will differentiate between them and, through a relay and motor system, knock the defective rivets to one side as they pass down a chute. Differences in magnetic or acoustic behavior can likewise be used to separate the sheep from the goats. Phototubes will detect irregularities in the width, thickness, or hardness of sheet metal, or pinholes that cannot be caught by the human eye.

Finally, electronic devices can be used not only to replace the human senses and muscles, but to veto human actions. The operator of a machine gets his hand too near the cutting tool. A light beam is intercepted and the machine stops before anything can happen. Industrial accidents are one of our chief enemies. The National Safety Council reports that from the time of Pearl Harbor to the spring of this year, industrial accidents killed 102,000 war workers, permanently disabled 350,000 more, and injured no less than 9,500,000. Anything that electronics can do to reduce these tragic totals will be welcome indeed.

Electronics will certainly play a large part in the new world and solve many industrial problems, but it may create new economic and political ones. Electronic devices in industry are, in great part, labor-displacing devices.

True, postwar electronics will create jobs in other fields, as in television, and perhaps by reducing manufacturing costs of many articles. But we have no guarantee that on net balance it will increase employment. If, then, we want progressive factories, we shall also need progressive thought about what we are going to do with those factories. Such questions will inevitably arise, and no electronic machine will provide the answers.

1 comment
  1. Bob says: November 14, 200712:34 pm

    this is what I do for a living. amazing how much of the above is still true, with some upgrading for computing power.

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