GENERAL DESCRIPTION.
The following general description of this method of turret turning has been prepared from data and information furnished by the manufacturers, the Cutler-Hammer Manufacturing Company.
The system consists of a differential set of spur gears entirely enclosed in an oil-tight casing, and operated in a grease bath. This grease bath cushions the noise and reduces the wear of the teeth to a minimum. The upper half of the differential gear case is made readily removable and is provided with a hand-hole for inspection and the insertion of grease.
The differential system is operated by two motors, one large and one small one, and each of variable speed. These motors always run in opposite directions and the direction of their rotation is not changed and they are so geared to the differential system of spur gears that the differential shaft always turns in one direction. This differential shaft turns the turret through the agency of a double magnetic clutch and two sets of gears connected to it and to the main turret shaft, one set driving the turret shaft direct, the other through an idler. This effects the reversal of rotation of the turret without change of rotation of the motors as indicated in Fig. 1.
The magnetic clutch, differential gear and reversing gears are mounted on a common bedplate and the motors separately mounted, the small one above the large and are connected to the flanges of the motor shafts in the differential case. A view of the gear which also shows the motor shaft flanges is shown in Fig. 2.
ELEMENTARY PRINCIPLE.
The elementary principle of the differential system is shown in Fig. 3.
The gear A is driven by the small motor and gear B by the large one in opposite directions as indicated. The gears CC are connected to the main differential driving shaft and are also free to turn each around its own shaft. The revolution of CC and in consequence the revolution of the driving shaft will depend upon the relative speeds of A and B, and at one certain relative speed there will be no revolution about the center of the driving shaft, though each of the gears CC will rotate about its own shaft.
When this particular ratio of speeds does not exist, CC with its driving shaft will turn, the speed depending upon the relative speeds of A and B. Thus suppose gear B had 72 teeth, gear A 32 teeth, then when the relative speeds of B and A were as 4 to 9, there would be no motion of rotation of the driving shaft, the gears CC simply turning on their shafts. If the speed of A was lowered, CC would take a direction of rotation as shown by the arrow t, its speed depending upon the ratio of speed of B to that of A.
The large motor always carries the turret load and the small motor acts as a speed regulating device and brake upon the differential and will usually be generating current instead of acting as a motor. The torque furnished by the large motor moves the differential shaft and consequently the turret by the braking effect of the small motor, or, in other words, the torque of the small motor tends to reverse the direction of the turret rotation. If the turret is locked and the differential shaft cannot move, the large motor drives the small one at a high speed and causes it to act as a generator. This is readily seen in the elementary figure. The small motor will always act as a generator when sufficient power is required in driving the turret to cause the large motor to drive the small one through the differential gearing. When the small machine generates current, it is thrown back upon the large motor and the current required from the power lines is approximately only the difference between that required by the large motor and the amount generated by the small one. If the small motor does not rotate, the large motor will drive the turret at a high speed.
Between the extremes of the turret being locked and no revolution of the small motor, or, in other words, under normal conditions, the large motor drives the turret at an intermediate speed, depending upon the torque required. When the small machine acts as a generator the torque required to drive it acts as a brake upon the differential and causes the turret to rotate, due to the difference in torque of the large and small motors. If the required torque is small, or the resistance to rotation is small, the friction of the gears is sufficient to furnish enough braking torque to turn the turret without the small machine acting as a generator; in which case it will then draw from the line only the small current necessary to practically rotate its armature idly. In case the turret load is entirely removed, the small machine would act as a motor entirely and help to overcome the friction of the gears.
MAGNETIC CLUTCH.
As has been stated, reversal of the turret is accomplished by a double magnetic clutch operating a set of reversing gears, and in the off position of the turret controller both sides of this clutch are de-energized, thus entirely disconnecting the driving gear from the main turret driving shaft although the motors and differential may be still operating at full speed. The clutch consists of a central body containing the two coils and is rigidly keyed
to the differential shaft. The armatures of the clutch are secured by cap screws to their gears which are fitted with bronze bushings and turn idly on the shaft when the coils are de-energized. The side thrust of the gears against the central portion of the clutch is taken up on bronze collars. When either one of the clutch coils is energized, its armature is attracted and held fast and the torque of the driving shaft is then transferred to the turret shaft through the corresponding gears, while the other gear and corresponding armature turns idly on the shaft.
The central portion of the clutch, its pole pieces and gears are of steel, as well as the discs holding the armatures to the gears, and the armatures themselves are cast iron to form a bearing surface against the steel poles. Three bronze collector rings are securely bolted to the central body and the pole pieces extend slightly beyond the surface of these rings and afford mechanical protection. A sheet metal casing extends over the whole clutch and prevents mechanical injury to the clutch or accidental short circuiting of the collector rings or brushes. The leads from the coils to the collector rings are made water-tight through the clutch casings.
MOTOR OPERATION.
The large motors, which, in the case of 12" turrets are 25 H. P. and of the 8" turrets 15 H. P. have a speed variation of about 2 to 1 by field control. The small motors for 12" turrets are 10 H.P. and for 8" turrets are 5 H. P. and they have a speed ratio of 3 to 1 by field control. The large motors operate from 400 to 800 R. P. M., the small motors from 300 to 900 R. P. M. The gearing within the differentials has approximately a ratio of 2 4 to 1, corresponding to the relative speeds of 400 and 900 R. P. M. This is seen from Fig. 4 where the details of the differential are shown in right-line form and where the driving gears of the large and small motors have respectively 72 and 32 teeth or a ratio of 9 to 4; these being in turn driven by other gears which have the same and equal ratio of 29 to 91 from each motor. Consequently, when the large motor is running at 400 R. P. M. and the small one at 900 R. P. M. there is no resultant motion of the differential shaft, which is the condition when the controller is in the off position.
The motor field leads are carried to the small master controller and the first movement of the controller strengthens the field of the small motor by cutting out a small section of resistance, reducing the speed of this motor slightly and causing the differential to be unbalanced and a very slow resultant motion of the differential shaft is produced. While the field of the small motor is being continually strengthened by cutting out resistance. the field of the large motor remains at its constant strength, and the small motor field is strengthened until the armature is running at about 300 R. P. M., the large one during the time the small one is changing from 900 to 300 R. P. M. running at about 400 R. P. M. At this time with the ordinary turret gearing from the main driving shaft, the turret will be turning at about 25° per minute. Further rotation of the trainer's controller adds resistance to the field of the large motor, the small one at this time remaining constant, increasing its speed until it is operating at about 800 R. P. M., when the turret is then turning at its maximum speed of 100° per minute.
MASTER CONTROLLER.
The whole operation of starting the motors, of rotating the turret in either direction and varying the speed is accomplished by means of a small master controller in the turret. None of the armature leads are taken to this controller but only the motor field and clutch leads and a relay circuit from the motor starting boxes and those are all carried in a lead of small interior communication cable.
Each turret is equipped with two complete driving units, each unit consisting of the large and small motors, the differential gear, double magnetic clutch, reversing gears and an automatic starting box. Both driving units are controlled by the one small master or trainer's controller and either set may be put in operation by means of a starting and throw-over switch on the controller. In addition to starting and stopping the motors, varying their speeds and reversing the turret rotation, the master controller also effects the resetting of the circuit breakers after overload by the operation of a throw-over switch.
An open view of the controller is shown in Fig. 5 showing the throw-over switch on the left at the top of controller and the controlling hand wheel at the top through the center. The speed regulation is accomplished by means of connections made on the drum cylinder and by the insertion of resistance in the shunt fields of either motor as may be required.
This resistance is self-contained in separate compartments in the base of the controller, and is made readily accessible by removal of the cover around this portion of the controller. The resistance is of the unit type, and entirely enclosed, preventing the discharge of sparks in the possible event of a burn-out of the resistance. A small stationary commutator is installed in the controller for the purpose of making the various field connections to the unit resistances below. The segments on one side of the controller are cross connected to the segments on the opposite side, so that the same resistance is used when operating the turret in either direction. A small brush holder, carrying a carbon brush, bears on the commutator segments and is revolved by the drum cylinder. The controller is provided with a star wheel, having indents only at the off position and the first running position on either side. No other definite positions are provided and the carbon brush may be moved freely from the first to the last commutator segments, of which there are about 80.
The small auxiliary lever which operates the throw-over switch is mechanically interlocked with the main operating wheel so that it is impossible to throw this lever and start the motors with the operating wheel in any but the off position. In case of a blowing, of the circuit breakers, it is simply necessary to turn the operating wheel to the off position and throw the starting lever to its off position, which resets the circuit breaker and the equipment may then be again immediately started as before.
One revolution of the controller hand wheel gives the complete range of turret speeds from 4° to woe per minute in either direction of rotation.
The throw-over switch is in principle essentially a throw-over knife switch and corresponds to a double throw knife switch with six blades as shown in Fig. 7. Each arm of the throw-over switch corresponds to one blade and is insulated from the remaining arms.
In the central position of the throw-over switch lever both driving units are at rest, but as the lever is thrown to either side a corresponding driving unit is started and complete connections are made to the driving motors and starting panels; the other driving unit and panel being entirely inoperative.
THE STARTING BOXES.
The automatic motor starting boxes are furnished in watertight casings and contain the necessary apparatus for starting the motors from the trainer's controller and bringing them automatically up to their proper speeds and placing them in readiness to train the turret. They contain four electrically controlled switches or contactors which provide automatic starting and stopping of the motors from the trainer's station. A view of a starting box is shown in Fig. 6.
These boxes are also provided with an overload device causing the contactors to open the circuit in case of overload and which may be reset from the trainer's controller.
Two of the contactors function as line switches and two as accelerators for cutting out the armature starting resistance which is mounted at the back of the panel. These two accelerators are equipped with relays called "individual series relays" which are set to drop their plungers at a predetermined amount of current, and as each plunger carries a disc for controlling the circuit to the solenoid of the next contactor, these relays regulate the time of cutting out the armature resistance and bringing the motors up to the required speed. This operation will be better understood when the wiring diagram is being considered.
WIRING DIAGRAM.
A complete diagrammatic wiring diagram is shown in Fig. 7, showing the wiring of the motors, motor fields, magnetic clutch, master controller, automatic starting box and the various leads connecting them. Only one unit is shown, the other being entirely similar in its operation.
The control wires connecting a panel to the drum controller are shown in a conduit and may be traced by the corresponding lettering of the wire given at the point where the wire enters and at the point where it leaves the conduit. For example, the wire at binding post E' enters the conduit and leaves the conduit at a point in the drum controller marked E'. Similarly the various connecting wires between the contact buttons on the reversing switch base and the drum fingers and wires leading to the starting panels are encased in a conduit within the drum controller. These leads may also be traced by the similar lettering.
METHOD OF OPERATION.
Starting the Motors.—To start the driving unit shown, it is necessary that the hand wheel of the controller should be in the off position, after which the throw-over switch is thrown in a clockwise direction. This movement connects the middle contact of each group with the clockwise outside contact button of that group. Thus P" is connected to PP', CC to CC', FF to F', E to E', etc. This connects the leads of the unit shown and entirely disconnects all leads to the other unit which is rendered inoperative.
The main power lines and leads to the motors, including resistances, relays, blow-out coils and overload coils are shown in heavy lines, while all auxiliary starting and controlling lines are shown in light lines.
Current from the main line comes to the terminal marked + line, through the blow-out coil of No. 1 clapper switch, then to and through the right-hand pilot fuse. Here the current divides; one part flows through the resistance XY, through the retaining coil of the overload magnet, through the single switch marked normal to the binding post PP' through the lead to the controller to the terminal in the drum marked PP' to the contact button PP' of the throw-over switch, to the center contact button P", to the terminal marked P" in the controller drum, through the lead to the terminal P" in the starting box, through the left-hand pilot fuse, thence to the terminal on the blow-out coil of No. 4 clapper switch, to the terminal marked — line and then to the negative main lead.
This above described circuit energizes the retaining coil of the overload magnet.
The second circuit from the lower point of the right-hand pilot fuse is led to the right-hand contact post of the auxiliary disc contact on the second clapper switch, then through the contact disc to a similar post on the third clapper switch and from this post via the disc to the upper terminal of the fourth or right-hand clapper switch coil. This terminal is also connected to the upper terminal of the coil of No. 1 clapper switch. From these upper terminals current flows through the coils of No. 1 and No. 4 clapper switches to the common lead which connects to the overload and then follows the path described by the first circuit back to the negative lead.
These clapper switch coils, Nos. 1 and 4, are energized by full voltage and they close immediately. The closing of these switches places the two motors in circuit with all the starting resistance. Current flows from the positive line through the blow-out coil of No. 1 clapper switch, through the switch proper and then through the main overload coil. From this point the circuit divides, but as the second and third clapper switches are open, the current flows through the series relay No. 1, through all the starting resistances to the point marked No. 3, then to the terminal marked Arm, then to the common point between the two armatures where it divides through the two armatures, then from the common connecting point to the terminal marked Arm in the right-hand side of the panel, thence through No. 4 clapper switch and blow-out coil to the negative line. This completes the circuit and the motors start as the fields are energized at the same time as follows:
The instant clapper No. closes, current flows to binding post E on the panel to the binding post E in the controller drum and then to contact button E' on the throw-over switch. From here current flows to the center contact button E which is connected to the drum contact finger E in the controller. Finger E is always in contact with the drum segment so that the entire drum cylinder is supplied with positive potential. The drum cylinder being in the off position as shown, finger F is in contact with the cylinder and consequently positive potential is fed through this finger to the contact button F', then to binding post F' in the drum and from there to the field terminal of the large motor F'. Current flows from here through the field of the large motor to the negative line through No. 4 clapper switch, and this field is energized with full potential.
The drum cylinder being of positive potential, the current, in addition to taking the circuit described above, flows to the commutator brush B which is mechanically and electrically connected to the drum cylinder, then through all the small motor resistance steps to finger FF in the controller, to center contact button FF on the throw-over switch, then to the contact button FF' and then to right-hand terminal FF' of the small motor field. Current then flows through the small motor field to the negative line through
No. 4 clapper switch. This energizes the small motor field at the same time that the large motor field is energized, but it is supplied with reduced voltage while the large motor field has full potential.
Acceleration- of the Motors.—The first rush of current through the series relay No. i causes it to lift immediately, raising the disc connecting the two contact posts. As the motor increases its speed, its counter electro-motive force increases causing the current to decrease and when it has decreased to a certain value, predetermined by the adjustment of the relay, the disc drops and makes contact between its two contact posts. When clapper switch No. 1 closes, it makes contact with the left-hand contact post of series relay No. 1, and current now flows from clapper switch No. 1 by way of the disc to the upper terminal of the switch coil of clapper switch No. 2, by way of the upper disc of clapper switch No. 3. The lower terminal of the coil of clapper switch No. 2 is connected to the negative lead previously described, so current flows through the coil and clapper switch No. 2 closes. The closing of this switch short-circuits the first section of armature resistance, that between No. 1 and No. 2, since the armature current can now pass directly from the overload coil through clapper switch No. 2 and series relay No. 2 to the point marked No. 2, instead of flowing through relay No. i and the first step of armature starting resistance. The cutting out of this section of the armature resistance provides the motors with a second current inrush, which speeds up the motors and lifts relay No. 2. As the accelerating current decreases again to a certain predetermined value, relay No. 2 drops and current now flows from clapper switch No. 2, by way of the relay disc to the upper terminal of the coil of clapper switch No. 3. The lower terminal of this coil is connected to the line of negative potential, so current flows through the coil and clapper switch No. 3 closes. This cuts out the remaining section of armature resistance, since the current can now flow directly from the overload coil through clapper switch No. 3 to the motor armatures. This gives the armatures another rush of current and they come up to their full speeds as determined by their shunt field strengths.
Protective Circuits.—The closing of clapper switch No. 3 opens its upper auxiliary disc and so cuts off the positive lead from relay No. r to switch coil No. 2 which allows clapper switch No. 2 to open. The opening of this switch does not affect the main circuit as it is no longer carrying current and the power required to energize the coil is saved. The opening of switch No. 2 cuts off the positive lead to the third clapper switch coil by breaking contact with the left-hand contact post of relay No. 2, but the coil of switch No. 3 still retains current through the resistance AB, since switch No. 3 is of positive potential and makes contact with the contact post B. The current in the coil of switch No. 3 is reduced by means of the resistance AB and this serves to prevent the coil from overheating.
It must be remembered that the coils of clapper switches No. 1 and No. 4 obtained their positive feed through the lower auxiliary contact discs of switches Nos. 2 and 3, consequently when No. 2 closed, this circuit was broken and it was also broken when No. 3 closed. The coil of switches Nos. 1 and 4 are energized, however, through the resistance CD, which is connected in parallel around the two auxiliary discs. This resistance reduces the current flowing through the coils of switches Nos. 1 and 4 and protects them from overheating. It will be noticed here that the motors could not have been started had either clapper switch No. 2 or No. 3 been closed for any reason when it was desired to start the motors, since switches Nos. 1 and 4 will not close on the reduced current flowing through the resistance CD. In other words, the switches will remain closed on a smaller current than that required to close them. This so-called interlocking circuit serves to protect the motors from undue current, such as would result if either switch No. 2 or No. 3 were closed previous to the line switches Nos. and 4.
Overload.—In case of overload the small overload switch opens and cuts off the negative lead of all four switch coils and thus positively opens the clapper switches, which in turn opens the motor circuit. The retaining coil is still energized, though the main circuit is opened, and the overload plunger will remain in the tripped position until the retaining coil is de-energized. This is accomplished by moving the throw-over switch to the " off " position which breaks the negative lead of all the control circuits. When the retaining coil is de-energized the overload plunger drops and the overload switch is again closed. The motors may be then started by moving the throw-over switch lever to the " on " position, when the motors will start as previously described.
Testing Switch.—The throw-over knife switch on the panel is used in testing out from the panel, as it carries the negative feed to the four coils and to the retaining overload coil. The motors may be stopped or the overload reset by opening this knife switch, since it interrupts the feed circuit the same as opening the connection between the contact buttons P" and PP' on the throw-over on the switch base in the drum controller. By throwing the knife switch to the " testing " position, circuit is established direct from the negative line to the overload switch; that is, the circuit P", PP' is by-passed and the motors started, irrespective of the motor controller. The shunt fields are energized even though the throw over switch is in the " off " position, since the E.F and FF circuits are closed, due to permanent connections between the outside contact buttons of each group and the adjacent buttons. E.E' and E" are connected when the lever is in the " off " position, as also are F.F' and F", etc.
The circuit breakers may be reset after overload by opening and again closing the knife switch, so that all the functions may be had by the knife switch control except the speed variation and the closing of the magnetic clutch circuits.
Speed Variations.—After having started up the motors by moving the throw-over switch to the " on " position, the hand wheel of the drum controller is moved in order to start the turret. If it is moved in such a direction as to cause the cylinder to make contact to drum contact finger CC, positive current is fed to finger CC, then to central contact button CC" of the throw-over switch, to button CC' and then to the terminal CC' of the magnetic clutch coil. The common terminals of the clutch coils are connected to the negative line and the clutch CC' is thus energized by full potential and power is transmitted to the turret. The large motor has full field strength and runs at its normal speed while the small motor has full weak field and runs at its maximum speed, and since the small motor tendency is to reverse the turret, the turret turns at a very slow speed.
As the hand wheel is turned still further, the commutator brush B moves over the commutator and gradually cuts out the small motor shunt resistance step by step, finger FF receiving positive current through the resistance steps 1, 2, 3, etc., which are gradually being cut out, since the brush is positive and is approaching step No. 1. This action decreases the small motor speed by increasing the field strength, the large motor speed remaining the same, which allows the turret to turn at increasingly higher speeds. When the brush has arrived at segment No. i all the small motor shunt field resistance is out of circuit and both motors are running at normal speed. Further movement of the hand wheel causes finger FF to make contact with the drum cylinder, thus feeding positive potential to the small motor shunt field. At this time, drum finger F rides off the drum cylinder, and receives its positive potential from segment No. 61, or through the large motor shunt field resistance steps Nos. 61, 62, 63, etc., as the brush rides over them and cuts resistance into the large motor shunt field. This gradually weakens the large motor shunt field and speeds up the motor, the small motor speed remaining the same, and this causes the turret to revolve still faster. This continues until all of the large motor field resistance is in circuit when the large motor will be running at its maximum speed, the small motor at its normal speed, and the turret will be turning at its maximum speed.
Reversing the hand wheel rotation reverses the cycle and the turret is turned at decreasing speeds until the " off" position of the drum cylinder is again reached, at which point the clutch coil CC' is de-energized and the turret stops, although the motors continue running. If the hand wheel is turned still further in the same direction, finger C will make contact with the drum cylinder and feed positive potential by way of the contact buttons C and C' through the conduit to clutch coil C', which energizes that side of the clutch and connects power to the turret the same as before, except the train of gears has an idler inserted which reverses the direction of rotation.
The commutator segments are cross connected so that a further movement of the hand wheel produces the same functioning and speed variation, as when being turned in the opposite direction. It is thus seen that the turret is reversed by means of the hand wheel and that the complete range of speed variation is obtained in either direction by one turn of the hand wheel from one extreme position to the other.
It should be noted that both clutch coils are de-energized in the " off " position which has the effect of stopping the turret quickly and accurately. Permanent connections are made between the field resistances and the positive finger E, so that if for any reason the brush B was lifted from the commutator, the field circuits would not be opened.
The motors may be stopped by bringing the drum cylinder to the " off " position and then moving the throw-over switch lever to the " off " position, which movement opens the negative feed circuit P.
In order to start the other driving unit which is identical with the one described, it is only necessary to move the throw-over switch lever, so as turn the throw-over switch in a counter-clockwise direction. This causes a cycle of operations identical with that previously described.
CARE OF MAINTENANCE.
The differential casing should be kept approximately half full of grease for the lubrication and the cushioning of the differential gears. The several grease cups in the various bearings should be kept filled also with grease, although in most cases, one filling of the grease cups will furnish sufficient lubrication for a long period.
The clutch rings and brush holder should be examined occasionally, and the space between the clutch rings kept free from dirt, chips, etc. At long periods the carbon brushes bearing on the clutch rings will require renewal.
Occasionally the covers should be removed from the automatic starting boxes and inspection made of all contacts, especially the disc contacts, to see that they are clean and that the parts make proper contact in operation. The auxiliary contacts on the contactors require renewal at very infrequent periods.
The master controller, which is the essential feature of both driving units, should receive care and attention and the commutator especially inspected at regular intervals to see that the contact between the carbon brush and commutator bars is good and that there is no danger of grounding between commutator segments, owing to the collection of dirt, etc. Accumulation of moisture or dirt upon this commutator may cause grounding between segments and tend to eat out the insulating mica between segments. In the case of the possible burn-out of a resistance unit, the same may be removed from the controller and spare unit inserted without disturbing adjacent units. In inserting new resistance, special care should be taken to see that the proper amount of resistance is in circuit, as the proper operation of the system depends upon the required amount of resistance in circuit on a given controller position. If, for example, a unit was removed and a new resistance unit of higher ohmic value inserted in the field of the small motor, it would tend to produce too high a speed of the small motor, which would unbalance the differential in the wrong direction, and tend to make the small motor instead of the large one drive the turret a thing to be avoided. If too much resistance is inserted in the field of the large motor, it will require the motor to drive the turret on the last controller position at a speed greater than 100° a minute and weakening its field to this point may tend to produce poor commutation.