US1476824A - Speed-control apparatus - Google Patents

Description

M. E. LEEDS SPEED CONTROL APPARATUS Dec. 11, 1923. 1,476,824 I Filed Jan. 22, 1919 .F'ICi 1 27 FIG: Z. 26 26 25 INVENTOR 37 m cga 2 A TTORNEY Patented Dec. 11, 1923.

UNITED STATES PATENT OFFICE.

MORRIS E. LEEDS, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO LEEDS 66 NORTH- RUP COMPANY, OF PHILADELPHIA. PENNSYLVANIA, A CORPORATION OF PENN- SYLVANIA.

SPEED-CONTROL APPARATUS.

Application filed January 22, 1919. Serial No. 272,435.

T all whom it'may concern."

Be it known that I, Monms E. LEEDS, a citizen of the United States, residing in the city of Philadelphia, county of Philadelphia, and *State of Pennsylvania, have invented a new and useful Speed-Control Apparatus, of which the following is a specification.

My invention relates to speed control apparatus comprising a centrifugal device or governor controlling co-acting contacts which may control any suitable circuit to effect a speed control, but which are employed more particularly to control the speed of an electric motor which drives the governor.

It is the object of my invention to pro-- vide speed control apparatus of the character referred to which shall be capable with great nicety to control the speed of a device, such as an electric motor and apparatus driven thereby, whereby the speed fluctuations may be reduced, for example, to the order of one-tenth of 1% or less, as required, for example, in a chronograph employed in measurementof flight of projectiles.

While my invention is applicable to various types of centrifugal governors, it is particularly applicable to apparatus such as disclosed in my prior Patent No. 1,057,- 436 and produces a marked improvement in nicety of speed control, in some cases the fluctuation from desired or critical speed being reduced to one-fifth to one-tenth of. that attained by apparatus such as described in said Letters Patent.

For an illustration of some of the forms my invention may take, reference may be had to the accompanying drawing, in which:

Fig. 1 is an elevational view, some parts in section, illustrating a centrif al governor embodying my invention an driven by and controlling the speed of an electri motor.

Fig. 2 is a plan view of one form of spring suitable for my invention before bending the same to the form shown in Fi 1.

lg. 3 is a side elevational. view of the spring of Fig. 2.

Fig. 4 is a fragmentary elevational view illustrating a modified form of resilient mounting for one of the governor contacts.

Fig. 5 is a fragmentary elevational view of a further modification of resilient mounting for the governor contact.

Fig. 6 is a diagrammatic view of one of various types of electric motor which may be employed and the control thereof by the governor contacts.

Referring to Fig. l, M is an electric motor whose armature or rotor is mounted upon and drives the shaft 1 mounted in the usual bearings 2, 2. Secured to the shaft 1 by the screw 3 is the coupling 4, which may be of insulating material, upon which is secured by screw 5 the worm 6 driving the gear 7 secured upon the shaft 8 having a bearing in the member 9. The shaft 8 drives any suitable device or mechanism whose speed is to be controlled with great nicety, though the shaft 1 may directly drive the device or mechanism whose speed is to be controlled. The shaft 10 coaxial with the motor shaft 1 is secured to the coupling 4 by screw 11. Secured upon the shaft 10 is the cylindrical hub 12 on the supporting member or bracket 13. On the arm 14 of the bracket 13 there is pivoted at 15 the lever 16 having secured thereto or integral therewith the lever arm 17 preferably screw threaded, upon which is threaded or otherwise longitudinally adjust-ably supported the governor weight 18. The lever arm 17 which with the lever arm 16 may be considered to form a bell crank lever, extends preferably substantially parallel with the axis of the shaft 10. To the lever arm 17 is attached one end of a spring 19, shown under tension, Whose other end is secured to the rod 20 extending through an arm 21 of the bracket 13, different tensions being given to the spring 19 according to the position of the rod 20 which is secured in any of its adjusted positions by screw 22.

The movable arm 16 carries the rotary and longitudinally movable contact 23 adapted to engage the spr' g mounted stationary contact 24 which ay be the lower surface of the free end of the easily yielding bowed leaf spring 25 or a separate contact piece, as shown, secured upon the free end of the s ring 25, whose other end is secured "to t e vertically adjustable screw or abutment 26 threaded in the arm 26 which may be carried by. the member 9, a nut 27 looking the screw 26 after-it has been adjusted to suitable position. A suitable stop, as 2 6 carried by screw 26, may be provided -.brush 3O bears upon the hub 12, of metal,

which is in electrical communication through the metal parts 13, 14 and 16 with the contact 23. The brush 30 is mounted in a socket in the conducting member or brush holder 31, the spring 32 keeping'the brush 30 in contact with the hub 12. One circuit wire, as 33, is connected to the brush holder 31, while the other circuit wire, as 34, is connected to contact 24 through the member 26, screw 26 and spring 25.

The relation of the spring 19 and weight 18 may be made anything suitable or desirable, as for procuring a stable, unstable or neutral governor, to all of which types of governor my invention is applicable.

The operation is as follows:

The motor M drives the shaft 10 and rotates the bracket or supporting member 13 and associated parts, the member 9 being sufficiently to the rear to allow free rotation. Accordingly the contact 23 rotates in engagement with respect to the stationary contact 24. When the speed of rotation exceeds a predetermined critical speed, the centrifugal force exerted by'the Weight 18 causes it to move outwardly from the axis of rotation in opposition to spring 19, thereby moving the lever arm 17 slightly in a counterclockwise direction about the pivot 15, an adjustable stop 16 on arm 21 serving to limit the downward movement of lever 16. The weight 18 is on a short lever arm, while the contact 23 is on a long lever arm, and therefore a slight movement of the weight 18 is accompanied by a relatively greater movement on the part of contact 23, with the result that upon a slight increase of speed above a predetermined critical speed the contact 23 is withdrawn from engagement with contact 24, breaking the circuit in which they are included.

The circuit including the contacts 23 and 24 ma be any circuit, as for example, such asin icated in Fig. 6, where the motor M is shown as a series motor having the armature A and the series field windings f. The motor M is supplied with current rom the conductors 35 and 36 extending from any suitable source of current. In series with the motor are the resistances 37 and 38. The conductors 33 and 34 connect the contacts 23 and 24 in a circuit shunting the resistance 38, which latter is in effect cut out of circuit when the contacts 23 and 24 are in engagement With each other.

The effect is therefore to change the amount of resistance in the circuit of the motor M as the speed increases above the desired critical speed, the motor then slowing slightly, with a resultant reengagement of the contacts, with a tendency again to increase the speed of the motor.

- It has been found that a governor such as above described, whether it be neutral, stable or unstable, but with the stationary contact 24 rigidly mounted as illustrated in the above mentioned Letters Patent, does not open and close its contact with the extreme nicety and certainty sometimes desired.- A properly behaving governor, particularly when neutral or unstable, should maintain the contacts in engagement with each other until the critical speed is reached, and then should completely and effectually separate the'contacts. -In the case of an unstable governor, at critical speed the centrifugal member should fly out to the extreme limit permitted by its stop. A governor with the stationary contact rigidly mounted as in said Letters Patent does not so behave, but on the contrary, the resistance at the contacts may vary through wide limits. In some cases the resistance at the contacts, or what may be compared to the resistance at -the contacts, ranges, relatively, from a fraction of an ohm to several hundred ohms, with resultant imperfect or incomplete circuit rupture and im erfection of control. This is believed to be due to toughening of the contact surfaces resulting from wear and sparking, causing the contacts to make intermittent contact and in effeet to bounce on each other or chatter as they revolve with respect to each other,.due-

to small irregularities in their engaging surfaces. The periods of the bouncing or chattering depend upon the difference between the force exerted by the spring and the centrifugal force and the moment of the moving system about the pivot, as 15. This difference between the two forces varies from a relatively strong force at speeds below the critical speed to practically zero at critical speed.

Whatever causes the bouncing or chattering occurs once for each revolution of the rotary contact; and it is believed that in practice bouncing or chattering is caused a plurality of times for each revolution. In order that the contacts shall not materially separatefrom each other before critical speed is reached notwithstanding the bouncfiig or chattering, it is necessary that they shall follow each other quite continuously notwithstanding irregularities in their contact surfaces. This is accomplished by to elongate the same distance.

making the spring 25 light or weak in the or to longitudinal movement of contact 23 Withoutaffecting the governor. For example, spring 25, especially in the governor illustrated, may yield a given short distance to a force which is about one-half to onetenth the force necessary to cause spring 19 And a similar relation may hold where spring 19 is replaced by gravity to oppose the centrifugal force exerted by weight 18.

The spring 25 and contact 24. as a resilient system, after having yielded or bounced away from contact 23 must very quickly and promptly return to normal position with respect to contact 23. This is accomplished by maki g the natural period of the resilient system short. The half period of vibration of the resilient system should be at least as short as and preferably considerably shorter than the time occupied for one revolution of the contact or governor shaft 10. By way of example merely, and Without limitation of my invention thereto, it may be stated that where the governor shaft 1t makes 53 i revolutions per second, the natural period of a half-vibration of the resilient contact system in the direction of longitudinal movement of the contacts, that is, in a direction longitudinally of the governor shaft, is preferably at least onetwenty-fifth of a second and may be with advantage one-fiftieth of a second; and it will be understood that the relative period of vibration may be even shorter.

It is also desirable that the mass of spring 25, or of spring 25 with contact 24. if a contact as 24 be mployed, shall be small, and preferably so small as not to affect the action or behavior of the rotating governor system, as by reaction thereon through Contact 23.

It will be understood, therefore, that my improved results are attained by using a spring contact system which preferably has small mam and which yields readily to the forces incident to the bouncing or chattering or to longitudinal movement of the rotary contact, without, however, materially disturbing the governor as regards the relation of the forces exerted by the spring 19 and the weight 18; and further, by making the natural period of the resilient sys tem so short that after yielding or bouncing restoration is so prompt that the contacts may be said to be substantially continuously in engagement with each other. By this arran ment the contact resistance is low and varies but slightly; and when the contacts separate the effectually electrically separate to pr uce practically infinite resistance between them.

When contact 24 is omitted, as it may be, the spring 25 itself directly contacts with contact 23; and in such case the characteristics of the yielding or resilient contact system 25 are the same as those above described.

While With the contact 24 rigidly mount-- ed as described in said Letters Patent very small fluctuation of speed is attainable, nevertheless by my improvements herein described the fluctuation in speed may be reduced to one-fifth or one-tenth of what it is, other things being the same, when the contact 24 is rigidly mounted. By the mprovements herein described the variation of speed from critical speed may be reduced to one-tenth of 1%, or even less.

As further improving the operation, the area of contact between contacts 23 and 2t is reduced as by making eitherof the contacts, as 23, conical at its end, as indicated.

In lieu of bowing the spring 25 as indicated in Fig. 1, the same may be disposed as indicated at 25*, Fig. 4-. a

By preference the spring 250$ Fig. 1 and the springs 25 of Fig. 4 may taper, aS indicated in Fig. 2, from its large end, where secured to the support, to the small end, where a contact as 24 may be attarhed. These springs may also diminish in thlC-KDQSS from the end where secured to the support to the contact end as indicated in Fig. 3. Figs. 2 and 3 show the spring 25 before bending to the form shown in Fig. 1, or as employed in Fig. 4.

While the bowed spring 25 of Fig. 1 is the preferred form, the contact 24 may also be otherwise resiliently mounted, as upon the end of a helical spring 39, as shown in Fig. 5.

As in the case of Fig. 1, the, contact 24 may be omitted in Figs. 4 and 5, and the ends of the springs 25 and 32 themselves contact with the rotary contact 28.

The hereinbefore described characteristics of the resilient or yielding contact system of Fig. 1 are preferably had also by the systems of Figs. 4 and 5.

While it is preferred that the yielding or resilient contact systems, comprising springs 25, 25 and 39, shall be stationary, it will be understood that by mere reversal such resilienit or yielding contact systems may be secured upon and rotate with the governor arm 16 with the contact surface of such system cooperating with a stationary contact.

What I claim is:

1. Speed control apparatus comprising a centrifugal governor, a contact, a resiliently yielding contact system, said contact and said system engaging each other in the axis of rotation of the rotating structure of said governor, said system having small mass and having a natural eriod of vibration longitudinall of the axis of rotation of said governor which is at least as short as the time of onerevolution of the rotating struc; ture of said governor.

2. Spied control apparatus comprising a centrifugal governor, cooperatin contacts controlled by the governor, one ot said contacts rotating with said governor and engaging another of said contacts in the axis of rotation, and a resilient mounting for least one of said contacts having a natural period of vibration which is at'least as short as the period of one revolution of said rotating contact, said contacts normally engag ing each other and separating upon excess of speed above a predetermined critical speed. i

3. Speed control apparatus comprising a centrifugal governor, cooperatin contacts controlled by the governor, one 0 said contacts rotating with said governor and engaging anotherof said contacts in the axis of rotation, and a spring supporting one of said contacts and constituting a system having a natural period of vibration which is shorter than the period of one revolution otsaid rotating contact.

4. Speed control apparatus comprising a centrifugal governor, cooperating contacts controlled by the governor, one of said contacts rotating with said governor and engaging another of said contacts in the axis of rotation, and a spring supporting one of said contacts yielding easily to the cooperating contact and constituting a system having a natural period of vibration which is shorter than the period of one revolution of said rotating contact.

5. Speed governing apparatus for preventing fluctuation of speed greater than one-fifth of 1% comprising a centrifugal governor, a contact, a resiliently yielding contact system, said contact and said system engaging each other in the axis of rotation of said overnor and one of them rotating with sand governor, said system yielding easily in a direction longitudinally of the axis of rotation of said governor, and having a natural eriod of restoration in said direction Whic is at least as short as the time of one revolution of said governor.

6. Apparatus for controlling the speed of an electric motor comprising a centrifugal governor whose speed corresponds with the speed of the motor, and motor control contacts disposed at the axis of rotation of said governor and one of them actuated by said governor, one of said contacts comprised in a resilient system having such characteristics that speed variation in excess of one-fifth of one per centum is prevented.

In testimony whereof I have hereunto affixed my signature this day of January, 1919.

MORRIS E. LEEDS,

Images