US2833941A - Automation system - Google Patents

Description

y 6, 1958 J. ROSENBERG ETAL 2,833,941

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AUTOMATION SYSTEM 1'7 Sheets-Sheet 17 May 6, 1958 Filed Nov. 2; 1955 United States Patent AUTOMATION SYSTEM Jack Rosenberg and Alexander F. Brewer, Pacific Palisades, and Thomas J. Scuitto, Santa Monica, Calif., assignors to General Dynamics Corporation, Rochester, N. Y., a corporation of Delaware Application November 2, '1955, Serial No. 544,478

46 Claims. or. 307-149 This invention relates to automation systems and, more particularly, to an improved arrangement for automatically controlling machine tools.

in the typical machine shop, the machining of a piece of metal to obtain a finished product having a desired form requires that a methods man lay down the procedures for cutting the metal into the required shape in considerable detail. These procedures are then followed by one or more machine-tool operators. Where a large number of the same item must be made, it would appear that the function of operators to continually supervise and control the cutting operations of a machine tool can be economically obviated by some form of control device which directs a machine tool through a cutting sequence. A number of systems have been both proposed and built for the purpose of automatically controlling the operation of machine tools. Thus, the replacement of the machinetool operator by the automatic-control system is one type of automation. Automation may be defined as the utilization of machineryto perform an operation automatically which was previously performed by human bemgs.

The automation systems for controlling motion which have been built hitherto have not been finding too great commercial success for a number of reasons. One of these is that the cost required for the installations is considerable. Another reason is that the accuracy of the results obtained is not as great in many instances as is required by the kind of product being machined. Still another great drawback on the mass use of these automation machines is that the instructions to the automation machine'in the steps to be followed in order to effectuate a desired finished product from the raw stock attain such complexities as to discourage and deter any prospective users. The process of instructing the automation-control apparatus to follow or proceed along certain cutting paths is akin to the process of programming a computer. In actual machine-shop practice, the directions to be followed by the machine-tool operator are laid out in detail by the methods man, who, as a result of his vast experience, knows what sequence of cuts or cutting paths should be followed to produce the desired result.

An object of this invention is to provide an automation system which is simpler and faster to program than those heretofore.

Still a further object of this invention is to provide an automation system which is simpler to operate than those heretofore.

Yet another object of the present invention is to provide an automation system which is simpler to construct than those heretofore.

Still another object of the present invention is to provide an automation system which is more inexpensive than those heretofore.

The presently known automation systems usually employ a medium, such as magnetic tape or perforated paper tape, upon which signals are recorded. The function of the recorded signals is to direct motors, for example,

which control the motion of a table upon which a workpiece is mounted relative to a cutting tool. The apparatus required in the machine shop to interpret the signals recorded in order to properly control the relative cutting tool and workpiece motions has been quite complex. This is not a desirable feature, since the vibration and noise attendant a machine-shop operation is usually such as to prevent or deter the continued operation of all but the most rugged types of equipment. While this invention, in those instances where a record is desired, may also employ a recording medium for the purpose of containing the instructions to be applied to the motion-controlling equipment, a further object of the present invention is to reduce considerably the complexities of the apparatus required at the location of the machine tool which is being controlled.

These and further objects of the present invention are achieved by providing a system wherein the programming information is very simply prepared and, further, the apparatus required for interpreting the programmed information is also extremely simple. For the programming of the computer, the layout man goes through substantially the identical procedure as he now goes through without automation apparatus. In other words, he proceeds to determine the desired operational sequence of cuts or cutting processes or motion paths for a tool relative to the workpiece which are required and prepares the drawings required. Each drawing may then be considered as being in a co-ordinate system, since dimensions from reference lines or edges are always provided.

The apparatus comprising an embodiment of the invention may include a source of periodic pulses from which pulses are applied to two divider means. The first of these divides the number of pulses obtained from the source by the differential of the equation of the desired motion path with respect to one of the co-ordinates. The second divider means simultaneously divides the number of pulses from the source by the differential of the equation of the desired motion path with respect to the other of said co-ordinates. The outputs from these dividing means may be directly utilized or may be recorded for future utilization. The data for finding the differential for each path is obtained by subtracting the co-ordinates at the beginning and at the ending of a path. These differences may be used to provide the numerical value of the dividers. Each divider means provides a train of pulses. Each pulse represents an incremental motion along a path such as that of the tool being controlled relative to the workpiece along one of the co-ordinates. Each train of pulses contains as many pulses as there are increments of motion required along a co-ordinate to complete the required operation which is the resultant of the motion along said two co-ordinates.

The pulse trains may be separately recorded, and the apparatus required at the machine tool may consist of a motor to drive the workpiece relative to the tool along each of the coordinates the required number of increments for which a pulse train is provided. Apparatus may be provided to furnish an output pulse for each increment of motion the workpiece is moved relative to the tool along a co-ordinate. A separate counter counts the recorded pulses which are applied to the separate driving motors. This counter (one for each co-ordinate) also counts the pulses obtained from the moving machine tool, subtracting pulses resulting from motion in the commanded direction and adding those resulting from mo tion in the opposite direction. Accordingly, it may be readily established, for example, whether or not the machine tool has efl'ectuated a required .cut amplitude, and any shortage or surplus of pulses due to machining difficulties or cutting-tool troubles or other causes can provide an alarm.

It should be appreciated that where only a single coordinate-path motion is required, one divider means is able to provide the output necessary for directing such motion. Also, where three co-ordinate-path motion is required, three divider means may be employed for providing the necessary control signals. 1

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

Figure 1 shows a straight-line graph to assist in an understanding of the invention;

Figure 2 shows an arrangement for deriving required number-representative signals from an adding machine;

Figure'3 is a block diagram of an embodiment of the invention employed to generate pulse trains for ordering motion along a straight line;

Figure 4 is a schematic and block diagram showing some circuit details for the embodiment of the invention shown in Figure 3;

Figures 4A through 4D show typical pulse trains which may be derived from this embodiment of the invention shown in Figure 3;

Figure 5 is a block diagram of an embodiment of the invention for generating control pulses for ordering motion along a circular path;

Figure6 is a schematic and block diagram showing some circuit details for the embodiment of the inventionshown in Figure 5;

Figure 7 is a block diagram of another embodiment of the invention for generating control pulses for ordering circular motion;

Figures 8A and 8B are schematic and block diagrams showing some circuit details for the embodiment of the invention shown in Figure 7;

Figure 9 shows typical pulse trains which may be derived from the embodiment of the invention shown in Figure 7;

Figures 10 and 11 are block diagrams of embodiments of the invention showing pulse generators for pulses for ordering parabolic motion;

Figure 12 is a block diagram of an embodiment of this invention showing a generator for control pulses for ordering a higher order curve motion;

Figure 13 is a block diagram of an embodiment of this invention showing a generator for control pulses for ordering a three-dimensional straight-line motion;

Figure 14 is a block diagram of an embodiment of the invention for executing the paths ordered by the control pulses generated;

Figures 15A and 15B are schematic diagrams of a motion digitizer and apparatus to prevent control pulses and motion-digitizer pulses from interfering with each other which are required in the embodiment of the invention shown in Figure 14;

Figures 16A and 16B are circuit diagrams of an error register and a digital-to-analog converter required in the embodiment of the invention shown in Figure 14; and

Figure 17 shows a typical workpiece mounted on a table, and the required cutting paths.

Straight-line generator In order to facilitate an understanding of this invention, it will first be explained in connection with generating and effectuating straight-line paths or motion for a tool relative to the workpiece. Its utilization for various types of curved cutting paths will readily become ap parent from the explanation that follows. Furthermore, the explanation will be directed to the automation of a machine tool, such as a milling machine, where the relative motion of the cutting tool and workpiece is efi'ectw ated by having a cutting head, which is stationary, and a table which moves to perform the required motion.

4 This should not be construed as a limitation upon the invention, since the principles explained here can readily be extended towards the automation of other machine tools or such diverse systems such as automatic displacement recording and reproducing systems or an automatic pen controlling system.

From elementary algebra, it can be established that the formula of a straight line is y=mx+b. The slope of the straight line can be obtained by differentiating y with respect to x, whereby is obtained; m is the value of the slope which for any given straight line is a constant. Considering Figure 1, it can also be readily established that the slope of a straight line, m, which extends between two points, p and 1 which have as their co-ordinates respectively (X Y (X Y is equal to the tangent of the angle 6 between the desired line and the x-axis. Mathematically, this can be readily expressed as tan 0=m= ra -x Ax Therefore, .Ay=y -y Ax=x -x Therefore, to go from point p to point p we can move simultaneously along the xand y-axes Ax and Ay in the relationship These co-ordinates are normally provided in a blueprint where measurements are provided from reference lines or edges. Thus, to effectuate a desired straight-line cut, if the co-ordinates of the beginning and ending of the path are known, the table of a milling machine may be directed simultaneously to move distances along the respective two co-ordinate axes, as expressed by the differences (x x and (y -3 to effectuate such a resultant cutting path.

At the outset, it is desired to move the workpiece and cutting tool relative to ane another in response to pulses an increment of motion for each pulse. A suitable increment may be considered as 0.001 inch. For the purpose of controlling the machine tool, a separate pulse train may be provided for motion along each co-ordinate. According to this invention, a pulse train has as many pulses as increments of motion are required.

Thus, if a straight-line cut of 10 inches along, for example, the x-axis, is required, then 10,000 pulses would be required in the pulse train. Similarly, if a straightline out of 5 inches along the y-axis is required, then 5,000 pulses in the pulse train are required. A millingmachine table may be driven along the xand y-co-ordinates by two separate drive screws. A pulse-responsive driving mechanism may be employed to drive each screw. The driving mechanism employs motors which preferably are servo motors. It can be appreciated that in order to make a desired straight-line out, both co-ordinate motion motors are simultaneously excited with a separate pulse train, whereby each train represents the motion required along a co-ordinate to provide a resultant relative table and cutting-tool motion to effectuate the required cut on the workpiece.

The problem now presented is to obtain two pulse trains, one for each co-ordinate motion driving motor, the pulse trains having the requisite number of pulses corresponding to incremental motions along a co-ordinate axis, which are required to obtain the proper resultant cutting path. These co-ordinates may be established when measuring a specimen by referencing dimensions to two co-ordinate baselines. A layout blueprint shows a required cut referenced .to two baselines which may be relatively rectangularly disposed with the distances to the point at which the cut is to begin and the point at which it is to end being shown. Thus, x -x and y2'y1 may be readily determined if the two rectangularly related baselines to which the starting and-ending points are referenced are considered as the x-. and y-axes. It is seen that to generate a line having the required slope m, a division is necessary.

It is well known that the output of a pulse generator may be readily divided by a counter. As an illustration,

a generator may provide 1,000 pulses per second, and a counter may be set to count ten pulses before providing an output pulse. The counter then provides 100 output pulses per second when the generator output is applied thereto. Thus, effectively, the generator output has been divided by 10. If we apply pulses from a pulse generator to two counters, we may derive from each of the counters a train of pulses which equals the number of pulses applied thereto from the generator divided by the count of the counter, or the number set into the counter for the purpose of determining the amount of the division. Expressed another way, the pulse rate f of the generator is divided by the scale of the counter. If one dividing counter is set to divide its input 1 by Ay, and the other of the counters is set to divide its input 1 by Ax, there will emerge from the Ax counter a train of uniformly spaced pulses at one rate while from the Ay counter will emerge a train of uniformly spaced pulses at another rate If we examine the ratio between these two rates, we see that Ay This is exactly the slope of the desired cut between points x y and x y To obtain such a path, a machine-tool table which interprets each pulse as an order to move by 0.001 inch along a co-ordinate must have simultaneously applied a y-axis drive totaling Ay pulses and an x-axis drive totaling Ax pulses.

The two output pulse trains from the respective dividing counters may be recorded for this purpose so that whenever the same operation is required, the recording can be employed for repeating it without further eifort. The recording medium may be of any type, but magnetic tape on which the electrical pulses are recorded is preferred. Because of the nature of the counting process,

the two pulse trains recorded on the magnetic tape are periodic in nature, which is to say that in any one direction pulses will be spaced uniformly in time. This is an advantage when considering the output motion of a servomechanism which is to be employed to drive the cutting table in response to the pulse train. It is much easier to achieve smooth motion with periodic pulses than with an aperiodic drive.

It should be appreciated that the slope of a straightline cut can be positive or negative. The directions to the servomechanisms employed for driving the worktable can order it to go in one direction for positive-slope cuts and in the opposite direction for negative-slope cuts. Accordingly, instead of two channels upon which two pulse trains for the respective two co-ordinates are recorded, four channels may be employed, two for each co-ordinate, one of the two being for positive motion direction and the other for negative, or the opposite, motion direction. The determination of in which of the two channels (two for X and two for Y) a pulse is to be recorded may be derived by sensing whether x x or y y provides a positive or negative difference.

As an illustration of one preferred source of input to the system, adding machine apparatus which may be modified in the manner shown in Figure 2 is used. This is employed to calculate the difierences x --x .'and' y --y- As previously explained, x -x is the diiference between one of two co-ordinates denoting the beginning and ending of a straight line and y -y is the difierence between the other of two co-ordinates denoting the beginning and ending of the same straight line.

Actually, for each subtraction, two separate electrical outputs are derived from the adding machine apparatus, one being signals representative of the co-ordinate difference (x -x or y y and the other being the sign of the difference. The most significant digit position of the adding machine is reserved and employed to provide sign information. By a most significant digit of a number is meant the highest order digit. For example, the most significant digit of 6,352 is 6. The most significant digit of 3,259,875 is 3. The most significant or highest digit position of the adding machine which is reserved for indicating the sign is the highest digit position of whch the machine is capable. It should be noted that adding machines may be made to have any digit-handling capacity desired. Regardless of this, the principles to be described apply. If a subtraction is made and the difference or answer is positive, the highest digit position will remain a zero, provided that the numbers being handled are not of a size to include the highest digit position. If a subtraction is made and the difference or answer is negative, then the highest digit position will be a nine or less, dependent upon how large the negative difference is. This will become more apparent from the following description of Figure 2.

Figure 2 is a drawing which represents by way of illustration how the differences which are obtained by employing an adding machine are converted into an electrical output which may be entered into a register shown in Figure 3. By way of example and to maintain simplicity in the drawing, only three of the many answer wheels in an adding machine are shown. The answer wheels are the wheels which are read when the answer to a calculation is required. The first answer wheel 210 represents the units answer wheel; the second wheel 212 represents the tens answer wheel; the third wheel 214 is the representative of the answer wheel in the highest digit position of which the adding machine is capable. Thus, there are shown a tens and units answer wheel and the answer wheel from which there is derived the information as to the sign of the answer.

In performing the required subtraction function, first there is entered into the adding machine the rninuend from which a second number, or subtrahend, is subtracted. Next, the subtrahend is entered and the subtraction process performed. The answer to the subtraction is represented by the angular position of the various answer wheels. These wheels bear numbers on their peripheries and represent the answer as seen through an opening in the housing of the adding machine (not shown). Regarding the answer wheels shown in the diagram more closely, these have been modified by placing insulating material (not shown) on the sides thereof and electrical contacts 216 on the insulating material, one of which is positioned opposite each one of the digits represented on the periphery of the answer wheel exceptthe 0 digit. These contacts are then all connected together by a common bus bar 217. The contacts and bus bar may be applied to the answer wheel sides, using printed circuit techniques or by any other suitable means. All the answer wheels employed in the adding machine are thus modified.

The answer wheel 214 for the highest digit position has a slightly different arrangement. It has the plurality of contacts as shown for the other answer wheels, except that there is also provided a contact 215 at the zero position which is not connected to the common bus 217 connecting the other contacts. Furthermore, the zero contact is larger than the others. Three fixed position brushes 218, 219, 220 are employed with the highest-digit-

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