US1939588A - Control system - Google Patents

Description

1933- F. c. BIGGERT, JR., ET'AL I 1,939,538

CONTROL SYSTEM Filed 001:. 2, 1931 Patented Dec. 12, 1933 CONTROL SYSTEM Florence C. Biggert, Jr., Grafton, and Robert H. Ellis, Pittsburgh, Pa., assignors to United Engineering & Foundry Company, Pittsburgh, Pa., a corporation of Pennsylvania Application October 2, 1931. Serial No. 566,518 12 Claims. ((1164-68) This invention relates to a control system and more particularly to an improved system for controlling the operation of what is commonly knownin the metal working art as a flying shear,

although as will be readily appreciated'from the following description it may be utilized with various other devices having similar operating characteristics.

In the cutting of moving stock by means of flying shears it is essential in order to produce cuts of accurate lengths to drive the shears in positive synchronism with the stock. To accomplish this end it has been the customary practice in the past to mechanically tie the driving mechanism employed to operate the feeding means with that of the shears. Such. arrangements where any appreciable degree of flexibility of speed control is demanded are exceedingly complicated and costly, as well as diflicult to manufacture and maintain. In an effort to avoid these difliculties, various forms of electrically controlled driving arrangements have been provided. These, however, as heretofore practiced, although of simple construction and affording a more flexible speed control, as well as a satisfactory solution to many of the difficulties common to the mechanical drives, have failed in their provisions of sufliciently positive and precise speed regulation between the shears 80 and the stock, to meet with the demands of accuracy in cutting required for many purposes.

With this in view, it is the primary object of this invention, generally stated, to provide an improved electrically controlled driving system 85 for apparatus, such as flying shears, which is positive in operation, simple of construction and which incorporates the advantages of both the older mechanical and previously practiced electrical drives without the disadvantages of either.

A further object is to provide an electrically controlled drive for flying shears in which provision is made for starting the shears in a manner to control the amount of material cropped from the leading end of the stock as the stock it is started through the shear, and also insure the first cut, as well as the succeeding cuts, being made when the shears are operating in positive synchronism with the stock.

Another object is to provide an electrically controlled and operative drive which is capable of absorbing the shock produced when the shear blades engage the moving stock as the cut is made and for doing so without injury to the driving elements.

These and numerous other objects, as well as the various other advantages andnovel features of the invention, will be apparent when the following detailed description is read in conjunction with the accompanying drawings, wherein the single figure shown illustrates what is now considered the preferred embodiment of the invention.

Referring to the drawing a common form of shear arrangement is shown which comprises a shear 1, a piece of stock 2, and a set of pinch rolls 3 for feeding the stock continuously through the shears. In place of the pinch rolls any other suitable work feeding device, such as a rolling mill may be substituted, and as shown here may be coupled directly to a driving motor 4 by means of a drive shaft 5 to receive its operating power.

In accordance with this invention shear 1 may be any of a number of well known forms of shears, for example, a drum type shear in which the knives mounted thereon are adapted to come into cutting engagement on intermittent revolutions of the drums or with every revolution thereof, or it may be a revolving blade form of shear equipped with a driving connection for adjusting the cutting speed of the blades independently of the overall rotary speed or other forms which are adapted to be operated from a constant or uniform main source of power supply. With such shears the lengths of the cuts are determined by the relative speeds of the feeding mechanisms and the shears 86 and for accuracy in cuts there must be no departure from the speed relation between the two.

In addition to cutting the stock into lengths of accurate size another requirement which is imposed upon flying shears such as are con- 90, templated by this invention is that they must include a provision for controlling the amount of crop end removed from the forward end of each piece of stock. To accomplish this the shears must be provided with means for varying their 5 speed between pieces of stock or they must be stopped and restarted during such intervals. In accordance with the latter form of operation the cutting blades must be in a suitable position relative to the leading end of the stock as it advances toward them and a reasonable control over the starting of the shears must be provided. This requires that the shears be stopped in a definite position after they complete their opm5 eration on each piece of stock and that they be restarted as the leading end of the succeeding piece of stock arrives at a definite point in advance of the shears. Also that the shears be accelerated rapidly to the exact cutting speed 110 suitable to the desired length of out before the cut is made.

The mass and corresponding inertia of flying shears and their associated parts are usually large and the-desired starting time from rest to cutting speed is usually small; hence, a high starting torque is required for acceleration. When the shears are once running at constant speed however, they require but comparatively low torque, but it is essential, as stated above, in order to produce accurate cuts that their speed relation to the stock be maintained absolutely constant.

With this in view, a motor 6 having a high starting torque and in which the torque de-- power to start the shear in the manner desired.

is also provided with sufficient power to overcome the friction of the shear and do the work of cutting at cutting speeds with some power in reserve. Preferably, it is a series type direct current motor or device having the characteristics of such motors, and in addition. to meeting such demands, is capable of doing so over quite a wide range of speed. The speed may be varied by simply inserting a variable resistance in the power circuit and thus avoid a speed change gear connection for variation of speed.

To provide for maintaining the speed relation between the shear and stock constant so as to insure accurate cutting, a synchronous machine '7 which is normally adapted to function as a motor and which has a pull-out torque in excess of the torque which motor 6 is capable of developing at cutting speeds, is also coupled to shear 1. For supplying alternating current to this motor which is synchronized with the speed of the stock or for electrically coupling it for synchronized actions with the stock feeding mechanism another synchronous machine 8 isemployed being electrically connected to machine '1 by a circuit consisting of conductors 9 and 11. This latter machine while normally adapted to function as a generator is provided with the same or similar pull-out and load characteristics as 'machine '7, and to insure its operating in positive synchronism with pinch rolls 3, it is connected through a speed change gear unit 12 and gears 13 and 14 directly to the drive shaft 5 of motor 4, the latterrmotor having sufficient capacity to supply the power demands of machine 8.

In the preferred operation of the system, machine 7 i is adjusted to function as a motor and to carry a small portion of the friction load imposed on the shear and is adapted to be electric'ally connectedv to machine 8 during the starting of the shear before motor 6 completely accelerates the shear up to cuttingspeed. In this way, machine 7 assists to some extent'in the acceleration of the shear and because of its high pull-out'torque prevents motor 6 exceeding the shear speed selected for a predetermined length of cut and also insures the speed of the shear being maintained in synchronism with that of the stock. For accomplishing such a result, machine 8 and speed change gear unit 12 may be considered as speed regulators and machine 7 .ment with switch 22 when both motor 6 and maby means of the speed change gear unit 12.

As illustrated in the drawing a source of current supply provided by supply mains Li and La may be employed for operating both motors 4 and 6, these motors, being connected thereto by conductors 15 and 16, and 17 and 18, respectively. To increase the speed control over the system a variable resistor '19 may be connected in the supply circuit of motor 4. For automatically starting and stopping the shear,'a pair of flag switches 21 and 22 are connected in parallel circuit relation to each other in the circuit of motor 6, for example, as in conductor 1'1, and are adjustably positioned in the path of travel of the stock in the front and rear, respectively, of the shear.

With such an arrangement, as soon as the leading end of stock 2 engages flag switch 21, motor 6 is energized to set the shear in motion. If desired, machine 7 may be started at the same instant by employing a magnetic contactor 23 for closing the circuit, connecting machines 8 and ,7 and placing the actuating coil of this contactor across motor 6 as shown, or in any other suitable position where it will be controlled by switches 21 and 22. As another altematlve, a ,centrifugal switch 24 may be coupled to machine 7 and its contacts connected in shunt relation with switch 23, the governor of the switch being adjusted to 1 close the circuit at any speed desired. 11 such provision is made, a hand switch 25 may be inserted in the circuit of switch 23 and opened in case the centrifugal switch 24 is employed. Also in such case a magnetic switch 20 may be inserted in series with switch 24 and adapted as shown to close with switch 21 and open with switch 22. Either type of control, however, will be adapted to set machine 7 in operation before the cut is made, and, preferably, for a purpose which will presently appear before cutting speed is reached. Under such conditions this motor functions to assist in the drive of the shear. Although if the speed of the shear exceeds the speed desired i when machine 7 is energized, the" latter instead of functioning as a motor will function as a generator. n the latter occurs, it sends its generated power back to shaft-5 by causing machine 8 to function as a motor and at the same time maintains shear 1 in synchronism with rolls 3.

When the trailing end of the stock passes switch 21, it will fall open. However, motor 6 and machine '1 will be maintained in operation until such. end of the stock passes out of engageshaft of motor 6 with its operating coil connected in series with that motor. In this way 14b the brake is automatically released when motor 6 isenergized and applied when it is deenergized.

It will be appreciated of course that other and more positive acting means of well'known form may be employed for positively positioning the blades each time the shear is stopped; that the switches 21 and 22 may have their position altered for different speeds of operation and that a re sistor 27 as referred to above may be employed to vary the speed of motor 6 to accord with any speed selected by changing gear unit 12 which selection determines the lengths of the cuts.

Another feature of this invention resides in its ability to relieve the shear of deleterious shocks at the instant of cutting. In flying shears, as is known, the time of cutting is very short and during such time quite heavy loads are imposed upon the shear parts. If the speed of the shear is rigidly maintained during this period, these heavy strains are transmitted throughout the driving mechanism, as is the case in a direct and complete mechanical drive, and greatly reduces the life of such a drive. If, however, the speed of the shear be permitted to retard slightly during the cutting instant, the kinetic energy of the shear parts assists in performing the cut and the stresses in the mechanism are greatly reduced.

It is characteristic of a synchronous motor that when it is driving a load the rotor lags its field by some part of a phase angle, and when being driven as a generator it leads its field by some part of a phase angle. In fact this lag or lead may amount to percent of a pole pitch. This permits an oscillation of a portion of a pole pitch when the machine is changed from motor to generator operation where the torques vary from positive to negative value. In accordance with this invention this characteristic of machine 7 is employed to advantage in making it possible to utilize the kinetic energy of the shear parts to assist in performing the cuts, it being appreciated that motor 6 also permits of such performance. To best employ such feature the proper selection of pole pitch and gear ratio between motor 7 and shear 1 is selected to provide the speed drop neeessary to take advantage of the kinetic energy of the shear parts to supply the cutting forces, and by such selection, as will be understood, machine 7 may be operated continuously as either a motor or a generator, or as both. After the cut is completed the combined torques of motors 6 and 7 will be available to reestablish the true running speed of the shear and by properly proportioning the loads on the motors there will be no jump- -g of poles and the exact shear rotation per minute will be maintained.

According to the provisions of the patent statutes, we have explained the principle and mode of operation of our invention and have illustrated and described what we now consider to be its best embodiment. However, we desire ,to have it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim: 1

1. The combination with a work machine of the type subjected to sudden impacts in. operation which is adapted to operate upon moving stock, of means for feeding stock to said machine, a driving motor'operably coupled to the work machine which is adapted to start it from rest independently of said feeding means and rapidly accelerate to operating speed, an electro-synchronous machine coupled to said work machine for positively controlling its operating sred, and a second electro-synchronous machine iven in synchronism with said feeding mechanism and electrically coupled to said first mentioned synchronous machine whereby ,positive synchronous operation is maintained between said stock feeding means and said work machine..

2. The combination with a flying shear of a driving motor having a comparatively high starting torque operably coupled thereto, and an electro-synchronous machine also coupled to said shear for controlling its operating speed.

3. The combination with a flying shear of a driving motor having a relatively high starting torque, which decreases as its speed increases, operably coupled to said shear for rapidly accelerating and driving it, an electro-synchronous machine positively coupled to the shear, and means for supplying alternating current of a given frequency to said synchronous machine to control the operating speed of the shear.

4. The combination of a flying shear having a series type direct current motor and a synchronous motor both operably coupled thereto, said series motor being adapted to carry the major portion of the shear load and to accelerate it from rest to operating speed in a relatively short period of time and said synchronous motoradapted to positively control the operating speed of the shear.

5. The combination of a flying shear having a variable speed motor operably coupled thereto for supplying its operating power, a synchronous machine coupled to it for positively controlling its cutting speed, and means for selectively connecting a source of synchronous power to said synchronous machine.

6. The combination with a flying shear of means for feeding stock to said shear, a driving motor having a relatively high starting torque for starting said shear from rest and accelerating it to cutting speed in a relatively short period of time, a synchronous machine coupled to said shear to control its cutting speed, means for automatically energizing said driving motor as the leading end of a piece of stock is fed to the shear, and means for automatically energizing said synchronous machine before the first cut is made.

7. The combination with a flying shear of means for feeding stock to said shear, a variable speed motor having a comparatively high starting torque coupled to said shear for starting and operating it, an electro-synchronous machine, having a pull-out torque in excess of the full speed torque of said motor, positively coupled to said shear, a second motor positively coupled to said stock feeding means, a second electrosynchronous machine positively coupled to said stock feeding means, and means for electrically connecting said electro-synchronous machines together to provide positive synchronous operation between the shear and the stock feeding means.

8. The combination with a flying shear of means for feeding stock to said shear, a variable speed motor having a comparatively high starting torque coupled to said shear for rapidly accelerating and operating it, an electro-synchronous machine positively coupled to the shear for controlling its speed, a second motor positively coupled to said stock feeding means, a second electro-synchronous machine also positively coupled to said stock feeding means, a flag switch 'for starting said first mentioned motor and arranged to be operated by the advancing end of a piece of stock before it reaches the shears, and means for automatically electrically connecting said electro-synchronous machines together before the first cut is made to provide synchronous operation between said shear and stock.

9. The combination with a flying shear of means for feeding stock to said shear, a variable speed ing motor, a flag switch adjustably arranged in the path of the stock in front of said shear and connected to start said first mentioned motor when the leading end of the stock engages the flag, means arranged to be operated automatically to electrically connect said synchronous machines together before the first cut is made whereby to provide positive synchronous action between the shear and stock and thereby insure accurate lengths of cut, and a second flag switch arranged to maintain the shear in operation until thetrailing end of the stock has passed a predetermined point.

10. The combination with a flying shear of means for feeding stock to said shear, a variable speed motor having a comparatively high starting torque coupled to said shear for accelerating it from rest at a rapid speed and supplying it with operating power, an electro-synchronous machine positively coupled to said shear, a driving motor 'coupled to said stock feeding means, a second electro-synchronous machine coupled to said driving motor, a flag switch adjustably arranged in the path of the stock in front of said shear and connected to start saidjirst mentioned motor when the leading end of the stock engages the 1 flag, means arranged to be operated automatically to electrically connect said synchronous machines together before the first cut is made whereby to provide positive synchronous action between the shear and stock to insure accurate lengths of cut, a second flag switch arranged to maintain the shear in operation until the trailing end of the stock has passed a predetermined point, and means for'stopping the shear at substantially the same point in its cycle of operation each time it is stopped.

11. The combination with a flying shear of means of feeding stock to it, a variable speed motor having a comparatively high starting torque coupled to said shear, means for varying the speed and starting characteristics of said motor, an electro-synchronous machine positively coupled to said shear, a driving motor positively coupled to said stock feeding means, a second electro-synchronous machine positively coupled through a speed change gear unit to said driving motor, and means for electrically coupling said electro-synchronous machines together when said shear is operated whereby to maintain the speed of said shear in positive synchronism with said stock feeding means and at a speed'relative thereto determined by the setting of said speed change gear unit. I

12. The combination with a flying shear of a direct current motor for starting and operating said shear, a synchronous motor positively coupled to the shear for controlling its speed, means for continuously feeding stock through the shear, a motor connected to positively operate said feeding means, a synchronous generator positively coupled to be driven in synchronism with said feed mechanism, and means for electrically con-- necting saidsynchronous motor to receive current from said synchronous generator and thereby maintain the speed of said shear in positive synchronism with that of said stock.

FLORENCE C. BIGGERT, JR. ROBERT H. ELLIS.

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