US2480102A

US2480102A - Cam generating machine

Info

Publication number: US2480102A
Application number: US787387A
Authority: US
Inventors: Louis L Weisglass
Original assignee: Simmon Brothers Inc
Current assignee: Simmon Brothers Inc
Priority date: 1947-11-21
Filing date: 1947-11-21
Publication date: 1949-08-30
Anticipated expiration: 1966-08-30

Description

Aug. 30, 1949. L. L. WEISGLASS CAM GENERATING MACHINE 4 Sheets-Sheet 1 Filed NOV. 21, 1947 INVENTOR: [cu/s L. We/sg/ax A T TOR/YE K Aug. 30, 1949. 1.. L. WEISGLASS 2,480,102

CAM GENERATING MACHINE Filed Nov. 21, 1947 v 4 Sheets-Sheet 2 I 3 i v I I l I hi INVEN TOR. \O Lou/'5 L. We/sg/ass 9 y v s M122? i. fi/MZMW A 7 TORNEY- Aug; 30, 1949- L. L. WEISGLASS 2,430,102

CAM GENERATING MACHINE Filed Nov. 21 1947 4 Sheets-Sheet S I IN V EN TOR. Lou/s L. We/sg/ass I Mai/Mm framvzy,

Aug. 30, 1949. 1.. L. WEISGLASS 2,480,102

CAM GENERATING MACHINE Filed NOV. 21, 1947 4 Sheets-Sheet 4 Mash/MM ATTORNEY.

Patented Aug. 30, 1949 UNITED STATES PATENT OFFICE Simmon Brothers, Inc, Long Island City, N. Y., a corporation of New York Application November 21, 1947, Serial No. 737,387

8 Claims. 1

The object of this invention is a machine which outlines or generates cams which have a configuration which follows substantially the formula 1 l 1 x y c where c is a constant, and .r and y are variables.

A preferred embodiment of this invention is shown in the accompanying drawings in which Fig. 1 illustrates a typical cam in a normal system of coordinates;

Fig. 2 is a plan view of the machine, partly in section;

Fig. 3 is a cross sectional view along the plane of line 33 in Fig. 2 drawn in a larger scale;

Fig. 4 is a cross sectional View along the plane of line 4-4 in Fig. 2 drawn in a larger scale;

Fig. 5 is a fragmentary longitudinal sectional view along the plane of line 55 in Fig. 2 drawn in a larger scale;

Fig. 6 is a longitudinal sectional view along the plane of line 66 in Fig. 2 drawn in a larger scale with some of the portions broken away; and

Fig. 7 is an electric wiring diagram.

Like characters of reference denote similar parts thoughout the several views and the following specification.

Referring to Fig. 2, all component parts of the machine are supported by and mounted on a base I I made from cast iron or some other suitable material. The mechanism comprises a number of spindles or lead screws supported in split bearings. The covers or upper parts of these split bearings are detachable and are, in the interest of simplicity, not shown in Fig. 2.

The cam is generated on a blank 12 by a rotatable tool l3. The blank is usually made from sheet metal such as sheet steel or sheet aluminum. The rotatable tool may be a simple steel point adapted to describe circles with a suitable radius.

A number of these circles inscribed upon the blank will envelope the desired cam configuration. A preferred construction, however, embodies not merely a cam tracing device, but a milling cutter such as shown in Fig. 2 so that the actual configuration of the cam can be milled by the machine. As illustrated in Figs. 2 and 5, the milling cutter I3 is mounted on a rotatable shaft I 4 which carries at its upper end a pulley PS. This pulley is connected by a belt 56 to a similar pulley 7 H which is mounted on and driven by a motor I 8. The ratio of the pulley diameter is, of course, so chosen that the milling cutter 14 rotates with a suitable speed. The diameter of the tool or, in

this particular case, the milling cutter must be equal to the diameter of the cam following roller with which the cam is intended to cooperate eventually.

Means must be provided to move the tool in a direction at right angles to its axis. These means comprise, for example, a bell crank with a first arm 2i and a second arm 22 substantially at right angles thereto. The extreme end of the first arm 2! carries the aforementioned rotatable tool with its spindle and the second arm 22 carries a pin 23 by means of which the bell crank is operatively connected to an actuating mechanism to be described later. If a motor driven milling cutter is used, it is expedient to attach the motor to the bell crank, and this has been shown in Figs. 2, 3 and 5. The bell crank is supported by a boss 24 which forms part of the base H, and the crank rotates around a stationary pivot 25 fastened to said boss.

The aforementioned blank I2 upon which the cam is to be generated is mounted to a slide 3| which will be called the first slide and which consists of two parts 3| and 32 connected by a bridge 33'. Both parts 3| and 32 carry threaded bosses, see Fig. 4, which engage rotatable lead screws 4| and 42 as will be described later. Part 3! is equipped with screws 35 by means of which the cam blank 12 can be attached to it.

The first slide with its cam blank can be moved by a mechanism which comprises two lead screws 4! and 42 mounted in split bearings attached to the base H. As pointed out before, the upper parts of these bearings are not shown in Fig. 2 in the interest of clarity. The two lead screws carry relatively large gears 44 and 45 in mesh with the small gear 46 which in this case has been shown to be driven by a hand crank 41. By turning the hand crank the operator can rotate both lead screws 4! and 4?. simultaneously and thereby move the first slide with the cam blank to any desired point. It will be appreciated that the hand driven mechanism, as shown, is merely the simplest example and that in reality it may be replaced by an electrical motor which, in turn, may be under the control of a push button or even an automatic device, causing it to move the first slide step by step in a systematic fashion. Two lead screws rather than one have been provided so as to be sure that the relatively wide slide moves uniformly on both ends without binding. Since the two lead screws obviously must have the same number of threads per inch, the bridge 33 connecting the two parts of the first slide 3| and 32 can be dispensed with if so desired.

A second slide 50 is provided which has

suitable projections

51 and 52. These projections engage between themselves the aforementioned pin 23 of the tool supporting bell crank. A movement of slide 50, therefore, causes a corresponding rotation of this bell crank and a movement of rotatable tool l3 in a direction substantially at right angles to the direction in which the cam blank moves.

The mechanism to move the second slide comprises a lead screw 6| which, through gears 52, 63, 54' and '65 is driven by a reversible electrical motor 66. This reversible motor may be of any convenient type but I have found that the simplest motor suitable for this purpose is an alternating motor of the so-called shaded pole type. This motor comprises a squirrel cage rotor and a stator which consists of a stack of laminations and a coil which is permanently connected to an alternating current line. Two shading coils are provided and the motor will rotate in one or the other direction depending upon whether one or the other of said shadin coils is short circuited. A motor of this type is schematically shown in the upper right hand corner of Fig. '7.

This reversible motor or, more specifically, its shading coils are controlled by an electrical network which causes this motor, by rotating in one or the other direction, to adjust the second slide automatically to the correct position for any point which the first slide may assume. This, in turn, gives th rotating tool an opportunity to describe a plurality of circles which envelope the correct configuration of' the desired cam.

The most important part of the network is an elongated resistor 70 on which slide two elec trical contacts ll and 12. Contact H is attached to the first and contact 12 is attached to the second slide. The starting point of the resistor, see Fig. 7, may be called 13. I call the portion of the resistor between 73 and T2 Rx. The portion between 12 and H is called R The net work is so designed that Rx and R are connected in parallel and their combined resistance is compared to a third resistor R0. Depending upon whether the combined resistance of the two parallel resistors Rx and R is larger or smaller than Re, circuit elements are actuated causing the reversible motor 66 to rotate in one or the other direction.

Physically the resistor 10 comprises a relatively long cylindrical insulator which may be a tubing on which a relatively large number of convolutions of thin resistance wire are wound. These convolutions must be evenly spaced with a small clearance between them so that the resistance per unit length is uniform and adjacent turns are not shorted. The cylindrical insulator, see Fig. 6, is supported b brackets and 76 which are, in turn, fastened to base I I. The sliding contacts Ti and 12 may be of any desirable type but it is important that they are so designed that they make contact with one wire convolution only, i. e., do not shorten two adjacent turns. I have shown for this purpose smaller rollers i! and 72', respectively, which must be made from a well conducting material such as copper or a silver alloy. These rollers are mounted on small pivoted levers as can be seen in Fig. 6, which are biased by springs which are not shown in the drawing and are pressed against the resistor, thereby assuring a good electrical contact.

It is well known that the resistance of two parallel resistors can be expressed by the formula:

7 value of resistors Rx and Re.

which can be written:

1 l FE The resistance R which depends upon the magnitude of both Rx and R is compared to a fixed resistance Re and means are provided to indicate whether R is larger or smaller than Re, and to adjust in accordance with this indication Rx and Ry until R=Rc. In this condition I can write the above formula The most convenient means to compare the values of two electrical resistors is the well known bridge circuit. l'wo additional resistors 88 and 8!, see Fig. 7, are, therefore, employed which complete the bridge circuit.

The two

opposite points

82 and 83 of this bridge are connected to a source of current. This source of current may provide either alternating or direct current, but direct current is more desirable since errors due to stray magnetic fields or the like can thereby be minimized. I have, therefore, merely as an example, shown a D. C. generator comprising a transformer with a secondary coil 90, an iron core 9i and a primary coil 92. The secondary coil has a center tap 93 and two

outer terminals

94 and 95 connected to the plates of a full wave rectifying tube 96. The cathode of this rectifying tube is connected to one terminal of the condenser 97, the other terminal of which is connected to the center tap 93. In order to provide a stable output voltage which is independent of small fluctuations of the line voltage, I use in a manner well known in the art a gas filled regulator tube 98 in series with a resistor 99. The positive output terminal of this D. C. generator is connected to point 83 and the negative terminal to point 82 of the bridge circuit. The two other points of this bridge circuit IE0 and Nil are connected to a device which indicates whether the value of the two parallel resistors Rx and R is larger or smaller than the This indicator may be of any desired description, but merely as an example, I have shown in Fig. 7 a two stage amplifier comprising a high vacuum tube I62 and a gas filled thyratron I03. Point l 50 is connected to the grid of I92, the cathode of this tube is connected to the negative and the anode to the positive terminal of a second D. C. generator which is very similar to the first one. I use another secondary N14 with a center tap H35 and two outer terminals Hi6 and H01. This secondary coil may be part of another transformer, but more conveniently it may be wound on the same iron core 9! of the first transformer described above. This transformer charges by means of a second full wave rectifying tube Hi8 two condensers. I09 and H0 separated by a resistance Hi, thereby forming a simple filter system. The output voltage is again stabilized by another gas filled regulator tube I I2 in series with a resistor 5 l3. Parallel to the gas filled regulator tube 1 I2 is a potentiometer H4, with two terminals H5 and it, the purpose of which will be described below.

As pointed out before, the grid of the high vacuum amplifier tube is connected to point I00 and the circuit is completed by a connection be- QABOJOQ tween the cathode of this tube and point IOI. The current passing the high vacuum tube I02, therefore, depends upon the potential that its grid assumes with respect to its cathode. This potential may be positive or negative, depending upon whether the combined value of the parallel resistors RX or Ry is larger or smaller than the value of the fixed resistor Re.

The second stage of the amplifier comprises the aforementioned thyratron I03. The grid of this thyratron is connected to a slidable contact IIO of the aforementioned potentiometer H4, and the cathode and anode, respectively, are connected to a source of alternating current which most conveniently is a coil II9 which is again wound on the iron core 9! of the transformer. A resistance I I1 is inserted into the connection between the terminal II5 of the potentiometer H4 and the cathode of the high vacuum amplifying tube I03, and a potential proportional to the current passing the vacuum tube I02 is consequently built up across this resistor I I1. In consequence of the way in which grid and cathode of thyratron I03 are connected, the potentiafiuilt up across resistor III tends to render the thyratron grid positive with respect to the thyratron cathode.

It can be seen that in a similar manner a voltage is built up between points H5 and H8 which renders the grid of the thyratron negative with respect to its cathode. The result of this arrangement is that the grid becomes positive or negative depending upon whether the voltage across resistance I I1 is larger or smaller than the voltage between points H5 and H8. A typical thyratron becomes current conducting as soon as the grid is less than 2 volts negative with respect to the cathode or, to put it differently, thyratron I03 will conduct current as soon as the potential across resistance I I1 is no more than 2 volts smaller than the voltage between points H5 and From these considerations the correct adjustment of the sliding contact I I8 of the potentiometer II4 can be deduced. This adjustment must be such that whenever the grid voltage of the vacuum tube I02 becomes zero, the grid voltage of the thyratron with respect to its cathode assumes the critical value, usually 2 volts, at which the thyratron is on the borderline of con ducting or not conducting current.

As soon as the thyratron begins to conduct current, the coil I20 of a relay will attract its armature. This relay has a normally closed set of contacts I2I and I22 and a normally open set of contacts I22 and I23. These contacts, in turn, are connected to the shading coils I24 and I25 of motor 66, respectively. As mentioned before, the motor is also equipped with a coil I20 permanently connected to an alternating current line. The respective connections between contacts I2I, I22 and I23 determine the rotation of motor 66. For example, as long as coil I20 is not energized, a contact exists between I2I and I22, short circuiting shading coil I24 and causing motor 66 to rotate, for example, in a clockwise direction. As soon as current passes coil I20, the contact between I2I and I22 will be broken and instead a contact will be established between I22 and I23, thereby short circuiting shading coil I25 and causing the motor to rotate in a counterclockwise direction.

The entire circuit, as described, can be connected or disconnected to the power line by means of .a switch I30.

Operation The operation of the device can be fully understood irom the following description:

The operator first, by turning crank 41, adjusts the first slide with the slidable contact II until the rotatable tool I3 is opposite the starting point of the cam. He then closes switch I30, see Fig. 1. In this position the resistance of the two parallel branches Rx and B of resistor I0 will not equal resistance Re and consequently the grid of vacuum tube I02 will assume some potential either positive or negative with respect to its cathode. Some current will pass the tube I02 which will cause a certain potential to be built up across resistance II! and this potential together with the potential of the left part of potentiometer II4, between points H5 and H8, will not equal the critical grid voltage of the thyratron, i. e., the thyratron will not be on the borderline of conducting or not conducting current, but it will definitely conduct or not conduct current. As a result of this condition, the relay coil I20 will either be energized or not energized. In the first case, contacts I22 and I23 are connected, and in the latter case, contacts I20 and I2I are connected. The closing of one of these contact pairs, in turn, short circuits one of the shading coils I24 or I25 causing motor 65 to rotate in one or the other direction. The rotation of motor 56 is transmitted through gears 65, 64, 63 and 2 to the lead screw 6| which, in turn, shifts the second slide 50. The straight line movement of this slide causes a rotation of the bell crank with its two arms 22 and 2I. This results in a movement of spindle I4 with the rotatable tool I3 in a direction substantially at right angles to the direction in which the two slides move.

The movement of the second slide 50 also moves the slidable contact I2 and thereby, as can be seen from the diagram in Fig. 7, both Rx and Ry are adjusted.

It has been explained above that resistor I0 comprises evenly spaced convolutions of thin resistance wire, and consequently, this resistor has a uniform resistance per unit length. If I call the proportionality factor m, I can therefore set It is therefore, only necessary to make Rc=c.m

to be able to modify the formula 1 l l RTE E to read Until this condition is reached, i. e., as long as R is larger or smaller than Re, motor 66 con tinues to rotate in a certain direction, and this direction, of course, must be so chosen that it tends to shift the second slide 5I towards the point of equilibrium. Eventually R begins to approach the value of Re, the grid voltage of the thyratron departs less and less from the critical value, and eventually reaches this value. As soon as this is the case, the formerly conducting thyratron becomes non-conducting, or vice versa,

and the condition of the relay contacts l2l, I22 and I23 changes in such a way that the formerly non-conducting pair becomes conducting, and the formerly conducting pair becomes non-conducting. This, in turn, opens the shading coil of motor 66 which was closed and closes the shading coil which was open, thereby reversing the direction of the motor. The motor now immediately drives slide 50 in the opposite direction. Since this takes place in the neighborhood of the point of equilibrium, only a very small movement in the opposite direction is necessary to pass the point of equilibrium again, whereby the entire mechanism as described functions again and reverses the motor again. It can easily be seen that the entire arrangement begins to oscillate, the motor rotating a few revolutions in one direction, shifting slide 50 with contact 12 a very small distance, reversing again sliding these two parts a small distance in the opposite direction, reversing again and so on. The amplitude of this oscillation can be made as small as desirable by winding very fine wire on resistance 10 and by making the amplifier very sensitive. The amplitude of the oscillation, if the contact rotor 12 is so constructed that it makes definitely contact with one convolution of resistance wire only, will be restricted to the distance between two adjacent turns of wire. This distance can without great difliculty be reduced to a few thousandths of an inch.

As soon as the equilibrium is reached, which is immediately noticeable by the rapid oscillations of motor 66, the operator opens switch I30, whereupon the entire system comes to a standstill. Slide 50 is now at the correct position in which R==Rc or in which and this position is accurate within plus or minus half the distance by which two turns of wire on resistor 10 are spaced apart. The correct position of slide 50 automatically assures the correct position of the rotatable tool I3 which either inscribes a circle on the cam blank, or in the case of the milling cutter actually mills this cam to size at this particular point.

The operator proceeds in this manner to determine the outline of the cam on the cam blank l2 point by point. He first moves the first slide by means of crank 41 and the associated mechanism, closes switch I30, and causes the second slide 50 to move towards the point of equilibrium in which As explained above, the mechanism will automatically move slide 50 into a position in which it oscillates around the point of equilibrium with a very small amplitude.

The outline of the cam can, in this manner be generated point by point and it has already been mentioned that the manually actuated crank driven mechanism is merely shown as a simple example, and that in reality, it can be replaced by an automatic mechanism which moves the first slide systematically step by step, leaving of course, suflicient time between movements to allow the milling cutter to do its work.

What I claim as new is:

1. A machine adapted to outline elongated cams with a configuration following substantially the formula 1 1 1 thy-t where at and 3/ are variables and c is a constant, said machine comprising a rotatable tool, adapted to describe circles which envelope said cam configuration, a mechanism adapted to move said tool at right angles to its axis of rotation, a first slide carrying a blank on which said cam is to be outlined by said tool, means to move said first slide, substantially at right angles to the direction in which said tool moves, to a number of selected points, a second slide cperatively connected to said tool moving mechanism and adapted to actuate same, means, including a reversible motor, to move said second slide in a direction parallel to the movement of said first slide, a stationary elongated electrical resistor with two terminals, a first sliding contact in current conducting relation with said resistor and fastened to said first slide, a second sliding contact in current conducting relation with said resistor and fastened to said second slide, disposed between one of the terminals of said resistor and said first sliding contact, an electrical connector connecting said one of the terminals and said first sliding contact, whereby two parallel resistors are formed between said connector and said second sliding contact, the resistance between the first terminal and the second sliding contact representing the variable IL, and the resistance between the first and second sliding contact representing the variable y, a resistor representing the magnitude 0, means to compare the value of said two parallel resistors to the value of said last named resistor, and to indicate whether said first value is larger or smaller than the second one, and means to cause said reversible motor to run in one or the other direction in accordance with said indication, whereby, for each selected point assumed by said first slide, said reversible motor automatically adjusts said second slide to a position in which the value of the two parallel resistors representing an and 3 equals the value of the resistor representing c.

2. A cam generating machine according to claim 1, said tool being a power driven milling cutter.

3. A cam generating machine according to claim 1, said mechanism to move said tool being a bell crank, one arm substantially parallel to the direction in which said slides move, said arm supporting said rotatable tool, and a, second arm substantially at right angles to said first arm and cperatively connected to said second slide.

4. A cam generating machine according to claim 1, said reversible motor being of shaded pole type, comprising a laminated stator, a coil adapted to be energized by alternating current, and two shading coils, adapted to be short circuited one at a time and causing said motor to rotate in one or the other direction.

5. A cam generating machine according to claim 1, said means to compare the value of the two parallel resistors representing a: and y to the value of the resistor representing 0, comprising two additional resistors, equal to each other, and a bridge circuit with four branches, the first branch formed by said two parallel resistors representing a: and y, the second branch formed the resistor representing 0, and the two other branches formed by said last named two additional resistors, a source of current connected to two opposite points of said bridge, a relay with a coil and a plurality of contacts, the two other points of said bridge operatively connected to said coil and said contacts causing said reversible motor to rotate in one or the other direction depending upon whether said relay is energized or not.

6. A cam generating machine according to claim 1, said means to compare the value of the two parallel resistors representing a: and y to the value of the resistor representing 0, comprising two additional resistors, equal to each other, and a bridge circuit with four branches, the first branch formed by said two parallel resistors representing a: and y, the second branch formed by the resistor representing 0, and the two other branches formed by said last named two additional resistors, a source of current connected to two opposite points of said bridge, an amplifier with two input terminals and two output terminals, the input terminals connected to the two other points of said bridge, a. relay with a coil and a plurality of contacts, said coil connected to the output terminals of said amplifier, and said contacts causing said reversible motor to rotate in one or the other direction depending upon whether said relay is energized or not.

7. A cam generating machine according to claim 1, said means to compare the value of the two parallel resistors representing :c and y to the value of the resistor representing 0, comprising two additional resistors, equal to each other, and a bridge circuit with four branches, the first branch formed by said two parallel resistors representing a: and y, the second branch formed by the resistor representing a, and the two other branches formed by said last named two additional resistors, a source of current connected to two opposite points of said bridge, a two stage amplifier with two input terminals and two output terminals, the input terminals connected to the two other points of said bridge, a relay with a coil and a plurality of contacts, said coil connected to the output terminals of said amplifier, and said contacts causing said reversible motor to rotate in one or the other direction depending upon whether said relay is energized or not, the first stage of said amplifier comprising a high vacuum tube and the second stage a gas filled thyratron.

8. A cam generating machine according to claim 1, said reversible motor being of shaded pole type, comprising a laminated stator, a coil adapted to be energized by alternating current, and two shading coils, adapted to be short circuited one at a time, said means to compare the value of the two parallel resistors representing :16 and y to the value of the resistor representing 0, comprising two additional resistors, equal to each other, and a bridge circuit with four branches, the first branch formed by said two parallel resistors representing a and y, the second branch formed by the resistor representing 0, and the two other branches formed by said last named two additional resistors, a source of current connected to two opposite points of said bridge, an amplifier with two input terminals and two output terminals, the input terminals connected to the two other points of said bridge, a relay with a coil and a set of normally open and a set of normally closed contacts, said coil connected to the output terminals of said amplifier, and said normally open contacts connected to one, and said normally closed contacts connected to the other of said shading coils, causing said reversible motor to rotate in one or the other direction depending upon whether said relay is energized or not.

LOUIS L. WEISGLASS.

No references cited.