US2115603A - Centrifugal switch - Google Patents

Description

April 1933- H. WILCOX 2,115,603

GENTRIFUGAL SWITCH Filed Oct. 10, 1934 2 Shets-Sheet 1 INVENTOR. R F

f g 3 i ATTORNEY.

Filed Oct. 10, 1934 2 SheetsSheet 2 FI A IUVVENTOR. 61 K L7 ATTORNEY.

Patented Apr. 26, 1938 PATENT OFFICE CENTRIFUGAL SWITCH Barry L. Wilcox, Cleveland, Ohio, assignor to The Electric Controller 8; Manufacturing Company, Cleveland, Ohio, a corporation of Ohio Application October 10, 1934, Serial No. 747,761

13 Claim.

This invention relates to an improved switch operable responsive to centrifugal force and to an improved feature which is applicable to all speed switches, whether centrifugal or pressure type, in which contacts open or close in response to changes in rate of rotation.

Speed switches of various kinds are now in use and are frequently employed to control the circuits supplying current to electric motors. It is a common practice to stop electric motors, both of the alternating and direct current type, by applying reverse power to the, motor while it is operating in the forward direction. This provides a very effective means for quickly stopping the motor, but if the reverse power is not interrupted at the instant of standstill, the motor may either reverse or continue to revolve in the forward direction. Such precision is usually beyond the ability of an operator and speed responsive switches either of the centrifugal type or thepressure type have been used to effect the interruption of reverse power automatically.

Centrifugal type speed switches, as usually constructed, have a movable member which is movable radially in response to centrifugal force generated when a revolving body of the switch is turned. The movable member is biased by means of a spring or otherwise to maintain it in the normal position except when the biasing force is overcome by centrifugal force. When the motor with which the switch is associated decreases in speed, the rotating part of the switch also decreases in speed, and, as the motor approaches a complete stop, centrifugal force acting upon the movable part of the centrifugal switch becomes so small that the biasing force acting on the movable member moves the movable member to the normal position. This causes a circuit through the centrifugal switch to be interrupted and causes the magnetic contactor in the line leading to the motor to open thereby interrupting the flowof the reverse current to the motor.

Oil pump, or pressure type, speed switches have a pump or pressure generating device which the interruption of power at the precise instant of standstill under varying conditions of load, temperature and voltage of the reverse power applied to the motor.

Speed switches of the pressure type are usually affected by temperature. A switch set for correct operation when cold will not be correct when the pressure fluid becomes warm. Speed switches which have metallic butt contacts are affected by vibration and may give premature operation due to momentary separation of contacts.

Speed switches in which the movable element moves on mechanical bearings or pivots and actuated by springs are affected by friction which introduces inaccuracies of operation.

I have found that this diiiiculty can be overcome by the use of a switch operable responsive to centrifugal force in which mercury is the movable element and the contacting device. The actuating force is the resultant between centrifugal force and the force of gravity and since both are a function of density, the balance or point of operation is independent of density, and hence independent of temperature which affects density.

The mercury as a contacting device moves radially outward on increasing rate of rotation and completely submerges the electrodes eliminating the effects of vibration.

The mercury also provides a frictionless contacting device which eliminates inaccuracies in operation caused by variable friction in the movable element.

The magnetic contactors, usually employed to control motors, have an electrical and mechanical inertia requiring a definite period of time to interrupt the power carried by their main contacts after the circuit to their magnet coils has been opened. This time interval is quite constant. For this reason it has been found necessary to adjust the speed switch contacts to open, on decreasing speed, at this same period of time before the motor comes to a stop, so that the contactors will interrupt the reverse power to the motor at the instant of standstill.

In practice, any particular motor stopping under the influence of reverse power may have various rates of deceleration so that the period intermediate the time when the motor reaches a given speed and the time that it comes to rest, will vary. If the speed switch is to initiate the interruption of the reverse power at a definite time before the motor reaches standstill, it must open its contacts at a higher speed when the rate of deceleration is high and at a lower speed when the rate of deceleration is low, thereby allowing the contactors a constant interval of time in which to interrupt the reverse power. I have found that these dimculties can be overcome by the use of a switch which is responsive not only to centrifugal force, but also to changes in the rate of rotation of the revolving members of the switch. I

It is an object of this invention to provide an improved switch operable responsive to centrifugal force.

Another object of the invention is to provide an improved switch responsive to centrifugal force and to changes in the rate of rotation of the switch.

A further object of the invention is to provide an improved switch operable responsive to centrifugal force and to changes in rotative speed, and in which the responsiveness of the switch to either centrifugal force or to changes in the rotative speed of the switch or to both may be adjustably varied.

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompany drawings, in which Fig. 1 is an elevational view of one embodiment of the switch provided by this invention.

Fig. 2 is a fragmentary sectional view taken substantially along the line 22 of Fig. 1.

Fig. 3 is a wiring diagram showing the circuit connections employed in one application of the centrifugal switch provided by this invention.

Fig. 4 is an elevational view of a modified form of the centrifugal switch provided by my invention, and

Fig. 5 is an enlarged fragmentary view of a portion of the switch shown in Fig. 4 with parts broken away and shown in section.

Referring to the drawings I have shown in Fig. 1 one embodiment of the improved centrifugal switch provided by my invention, and, as therein illustrated, the switch comprises a rotating shaft indicated generally at I, this shaft preferably being disposed to rotate about a substantially vertical axis. The shaft I is supported in bearings in the arms 3 and 4 of the frame indioated generally at 5. The frame 5 may be of any desired construction and preferably has a portion 6 adjoining the arms 3 and 4 and adapted to be secured to a suitable support, not shown. The shaft I has a bevel gear 8 secured thereon and meshing with the gear 9 mounted on the end of the shaft I [I which is supported in suitable bearings in the frame 5. The shaft I0 is driven either directly or indirectly from the motor to be controlled by any suitable means, as by a belt running on the pulley II which is mounted on the shaft I0. As will be understood when the pulley II is revolved the gear 9 turns the gear 8 and causes the shaft I to rotate.

Mounted on the shaft I are a pair of metallic disks I3 and I4 which are spaced apart by the fiber bushing I5 and which are held in place by means of the fiber or insulating bushings I5 and I1. A bracket I8 is mounted on the disk I4 adjacent the periphery thereof and is held in place by means of screw I9, the bracket I8 being rotatable about the axis of the screw IS. A clamp, indicated generally by the reference character 25, is secured in the bracket I8 so as to be pivotable on the screw 2I carried by the bracket l8. A glass tube 22 is held in the clamp 20. The tube 22 has a pair of contacts 23 and 24 secured thereanaeos in, these being positioned at the radially outer end of the tube. A small quantity of mercury indicated at 25 is sealed within the tube, the merweight indicated at 29 is secured to the rlisk I4.

to counterbalance the weight of the switch mechanism so that the switch will be dynamically balanced when it is revolving.

A block of insulating material 30 is secured to the frame portion 5 by suitable means, not shown, and a pair of brushes 3| are secured thereto. Each of the brushes 3i comprises a short piece of resilient metal which is provided with a block of suitable brush material, as for instance carbon, indicated at 32, and which engages one of the disks I3 or I4. The brushes 2| are secured to the insulating block 30 by means of screws 22 which also provide means for the attachment of the circuit connections leading to and from the switch.

In operation the shaft I is revolved and the mercury 25 contained within the tube 22 is thrown outwardly so that it submerges the contacts 23 and 24 to complete a circuit therebetween. The speed at which the shaft I must revolve before the mercury 25 is thrown outwardly will depend upon the angle at which the tube 22 is disposed and this may be adjustably varied by pivoting the clamp 20 on the axis of the screw 2|. If the tube 22 is in a comparatively horizontal position the mercury 25 will move outwardly at relatively low rotative speeds of the shaft I, as the force of gravity which must be overcome by the mercury in order to move outwardly will be relatively small. Similarly, if the tube 22 is in a position more nearly approaching the vertical the mercury 25 will not move outwardly until the rotative speed of the shaft I is relatively high. Likewise, when the shaft I is rotating at a speed at which the mercury is located at the outer end of the tube 22 and the rotative speed of the shaft I is decreased, the speed at which the mercury will move radially inwardly will depend upon the position of the tube 22, this speed being relatively high when the tube is in a position approaching the vertical and being relatively low if the tube is in a position approaching the horizontal.

It will be seen, however, that with any given adjustment of the tube 22 in the radial plane the rotative speed of the shaft I at which the mercury will move from the radially inner portion of the tube to the radially outer portion of the tube, will be relatively higher than the rotative speed at which the mercury moves from the radially outer portion of the tube to the radially inner portion of the tube, because, when the mercury is at the radially outer end of the tube the radius of rotation of the mercury, on which the centrifugal force depends, is greater than when the mercury is at the inner end of the tube. Therefore with any particular adjustment of the tube 22 a higher rotative speed of the shaft I is required to cause the mercury to move from the inner end of the tube to the outer end of the tube than is required to cause the mercury to move from the radially outer end of the tube to the inner end.

- The speeds of the shaft I which are effective to cause movement of the mercury ll as a result of centrifugal force may be adjustably varied by adjusting the tube 22 on the axis II to vary the angular inclination of the tube in the radial plane. With the tube in the radial plane the mercury will not be affected by the angular acceleration or deceleration of the shaft I. In the switch provided by this invention the tube It is turned out of true radial plane in order that operation of the switch is responsive to changes in the rate of rotation of the shaft I.

The podtion of the tube out of the radial plane is clearly illustrated in Fig. 2 of the drawings where it will be seen that the inner end of the tube is located rotatively in advance of the outer end of the tube. The position of the tube with respect to the true radial plane can-be adjustably varied by rotating the bracket I8 about the axis of the screw I9 and it can be held in the adjusted position by tightening the screw l9.

In operation, when the shaft I is rotating at a relatively high speed, with the mercury 25 located at the radially outer end of the tube 22, if the speed of rotation of the shaft I is then decreased, the angular speed of the shaft at which the mercury 25 will move inwardly is determined by the resultant of the following forces; the component of the centrifugal force acting parallel to the longitudinal axis of the tube in an outward direction, the component of gravity acting parallel to the longitudinal axis of the tube in an inward direction and the component of the force of deceleration of the mercury acting parallel to the longitudinal axis of the tube also in an inward direction. The mercury 25 will be urged outwardly by the continually decreasing centrifugal force generated as a result of rotation of the mercury and it will be urged radially inwardly by gravity tending to cause the mercury to flow to the lower end of the tube which is the radially inner end, and the force of gravity will be supplemented by the inertia of the mercury if it-were not subjected to this force.

which will tend to cause it to flow to the radially inner end of the tube which is rotatively in advance of the radially outer end. The magnitude of this latter force will depend upon the rate of deceleration of the shaft I. If the shaft I is decelerating rapidly the component of the force of deceleration acting on the mercury in an inward direction will be relatively great, and this will cause the mercury to move inwardly at a somewhat higher rotative speed of the shaft I than the speed at which it would move inwardly Likewise if the shaft I is decelerating slowly the effect of inertia on the mercury will be relatively small, or almost negligible, and the mercury will not move inwardly until a somewhat lower rotative speed of the shaft l is obtained.

Because of this method of operation the time interval intermediate the time at which the switch operates, and the time at which the motor stops turning, will be maintained substantially uniform irrespective of the rate of deceleration of the motor. If the motor decelerates rapidly, this switch opens at a relatively high rotative speed, while if the motor decelerates slowly the switch does not open until somewhat lower rotative speed is obtained. The mechanical and electrical inertia of the magnetic contactors controlling the flow of current to the motor and hence controlling the application of reverse current to the motor is substantially constant at all times, and the centrifugal switch which I have provided can be accurately adjusted so as to open the circuit to the contactors at the proper time interval before the motor stops turning to insure that the magnetic contactor will open the circuit to the motor at approximately the instant the motor-comes to a complete stop, and because of the construction of the switch provided by this invention it will always accomplish this result, regardless of changes in operating conditions which may produce changes in the rate of deceleration of the motor.

In Fig. 3 I have shown one set of circuit connections which may be employed with the switch provided by this invention. As therein illustrated the current is supplied by the wires 40 and I, the circuit to the motor being controlled by a magnetic contactor having a winding 42 and contacts 42a. The line 40 is connected to the armature 43 through forward and reverse contacts F and R, while the line 4| is connected to the series field H through an acceleration unit indicated generally at 45, which may be of any well known construction and need not be described in detail. The series field 44 is connected to the armature 43 through forward and reverse contacts indicated at F and R. The forward and reverse contacts F and R are controlled by the windings F and R, which are controlled by the manually operable switch lever 40, which may be moved to a position to complete a circuit through either winding to close either set of contacts and thereby determine the direction of the flow of current to the armature. A manually operable switch indicated at I! is placed in the circuit between the winding 42 and the wire 40, and when this switch is closed a circuit is established through the winding 42 to the wire I, and when this winding is energized the contacts "a are closed, thereby completing a circuit through either the winding F' or R', depending upon the position of the switch lever 46. When the winding F' is energized the contacts F controlled thereby are closed, completing a circuit to the motor and causing the motor to rotate the centrifugal switch 50 in the direction of the arrow shown in Figure 2. As soon as the speed of the motor passes a predetermined point the mercury in the tube of the centrifugal switch is thrown outwardly to complete a circuit through this switch. The centrifugal switch maintains the circuit through the winding 42 after the manually operated switch 41 is released.

When it is desired to stop the motor the switch lever 46 is moved to the opposite position to 'deenergize the winding 'F' to open the contacts F, and to energize the winding R to close the contacts R. This effects a reversal of the flow of current to the armature and causes a rapid deceleration of the armature l3 and also of the centrifugal switch which is driven from the armature. When the speed of the motor decreases to a certain value, depending on the adjustment of the centrifugally operated switch and on the rate of deceleration of the motor, the contacts of the centrifugal switch are opened, thereby interrupting the circuit through the winding 42, openingthe contacts 4211' and interrupting the circuit through the winding R. This causes the winding R to be de-energized and allows the contacts R controlled thereby to be opened.

The time interval intermediate the opening of the circuit through the winding 42 and the opening of the contacts R will be substantially con stant and will depend upon the mechanical and electrical inertia of the contactor controlled by to open at a substantially fixed periodbefore the motor stops, this'period being equal in length to that required by the contactors to operate so as to interrupt the flow of reverse current to the motor at the instant the motor stops turning; This will prevent reversal of the motor due to the continued application of reverse current to the motor after it has stopped rotating and it also prevents coasting of the motor due to the interruption of the reverse current before the motor has stopped revolving. As the switch is responsive to changes in rotative speed of the motor as well as to centrifugal force the switch automatically adjusts itself to any changes in operating conditions which affect the rate of deceleration of the motor.

In Fig. 4 I have shown another embodiment of the switch provided by my invention. This switch is generally similar in construction to that shown in Fig. 1 and comprises a frame indicated generally at 5| in which is rotatively supported ashaft 52, the frame 5| being mounted so that the axis of the shaft 52 is substantially vertical. A gear 53 is secured on the shaft 52 and is driven by the gear 54 which is mounted on the shaft 55, which is supported on suitable bearings in the frame 5| and which may be driven either directly or indirectly from the motor to be controlled by any suitable means as by a belt running over the pulley 55. A fiber or insulating sleeve 51 is fitted on the shaft 52 and three metallic disks 58, 59, and 50 are mounted on the sleeve 51 and are held in place by fibre or insulating bushings 6|, 52, and 53.

The disk 59 is somewhat thicker than the disks 58 and 60 and is provided with a pair of threaded apertures 64 extending radially of the disk 59 at an angle of approximately 45 to the axis of the shaft 52. In each of the threaded apertures 64 is mounted a threaded bolt or stud 65 having a bracket indicated generally by the reference character 55 secured on the end thereof, while a lock nut 51 is mounted on the stud 65 so that it can be tightened against the face of the disk 59 to hold the bracket 66 in adjusted positions.

The bracket 66 is preferably formed of sheet metal and has an arm 65' and'an angular portion 58 through which the head of the stud 55 extends. The arm 65' is provided with a pair of arcuate slots 69. The contact elements employed in this switch are generally similar to those employed in the switch shown in Fig. 1 and each comprises a sealed tube Hi supported by a bracket 55 and held by a pair of blocks H having recessed portions adapted to receive the tube 10. The blocks H are also provided with apertures through which extend bolts 12 which also extend through the arcuate slots 69 in the bracket arm 55'. As will be understood, when the bolts 12 are tightened the blocks H are pressed firmly into engagement with the tube 10 to hold the tube in position. The plane of the tube relative to the horizontal can be adjusted by loosening the bolts I2 and moving the bolts in the arcuate slots 59. This effects movement of the tube 10 about the axis 13, which lies in a plane extending substan-' tially perpendicular to the plane of the axis of the bolt 55, and allows the radially inner and outer ends of the tube III to be adjusted vertically relative to each other. A quantity of mercury indicated at is sealed within the tube 10 while the contacts 15 and 11 extend into the tube 10 so as to be engaged by the mercury to complete a circuit therebetween when the mercury moves to the radially outer end of the tube 19.

One of the contacts from each of the tubes ll is connected to the bracket and therethrough to the metallic disk 59, while the other contact on one of the tubes I0 is connected to the disk 59 and the other contact on the other tubes 19 is of switch is much easier to adjust than that shown in Fig. 1. In the switch shown in Fig. 1

after the tube is adjusted either about the axis l9 or 2| adjustment of the tube about the other axis affects the first adjustment, with the result that accurate adjustment of the tube is very difficult, and this problem is overcome in the form of switch shown in Fig. 4. In the type of switch shown in Fig. 1 the position of the tube 22 preferably is first adjusted about the axis 2|, the tube being previously moved about the axis l9 so as to be in a substantially radial position. The adjustment of the tube about the axis 2| is then made and this regulates the operation of the switch in response to centrifugal force. Next, the position of the tube is adjusted about the axis l9 to regulate its response to changes in the rate of rotation of the shaft the radially inner end of the tube being turned rotatively so as to be in advance of the radially outer end of the tube. However, when the adjustment of the tube about the axis I9 is made the radially outer end of the tube is moved inwardly radially thereby reducing the magnitude of the centrifugal force operating on the mercury and altering the previous adjustment made by adjusting the tube about the axis 2|, accordingly a slight readjustment of the tube about the axis 2| might be necessary to compensate for the change in the effective centrifugal force due to rotating the tube 22 out of the radial plane.

In the type of switch shown on Figs. 4 and 5, the adjustment can best be accomplished by the following method. The bracket 85 is adjusted so as to position the tube 10 in a substantially radial plane of the shaft 52, and the tube III is then adjusted about the axis 13 and it is held in the adjusted position by tightening the bolts 12. This regulates the response of the mercury 15 to centrifugal force and controls the operation of the switch in response to slowly changing speeds. Next the position of the tube I0 is adjusted for responsiveness to changes in the rate of rotation of the shaft 52. This is accomplished by rotating the bracket 56 and the bolt 65 about the axis of the bolt which extends iira plane at substantially 45 to the axis of the shaft 52. This causes the inner end of the tube 19 to be moved rotatlvely in advance of the outer end of the tube 10 and also moves the radially outer end of the tube radially inwardly slightly so as to reduce the magnitude of the centrifugal force operating on the mercury. This, however, is offset 'so as not to alter the first adjustment of the tube because the radially inner end of the tube is raised slightly and the radially outer end of the tribe is lowered slightly so that the effect of gravity tending to move the mercury radially inwardly is slightly decreased, thus maintaining the first adjustment.

While the switch of the type shown in Fig. 4

auaooa of switch provided by my invention is not limited to the use of a pair of switch units, but that-one of these units may be omitted and a suitable counter-weight substituted for it. Where a pair of switches are employed, one of the switch units controls the a plication of current to a motor for one direction of rotation while the other switch controls the application of current to a motor for the other direction of rotation. The tube 10 of one of the switches has its radially inner end rotatively in advance of the radially outer end for one direction of rotation, while the other tube has its radially inner end rotatively in advance of the radially outer end for the opposite direction of rotation. The switches are herein shown as connected in series and would be substituted for the single switch indicated at III in the diagram shown in Fig. 3. These would then control the circuit to the motor, the opening of the circuit being effected by the switch which is set to control that particular direction of rotation.

From the foregoing it will be seen that I have provided an improved switch responsive to the force of gravity, centrifugal force and responsive also to changes in the speed of rotation of the switch and in which the responsiveness of the switch to centrifugal force and to changes in the speed of rotation may be adjustably varied. It will also be seen that I have provided an improved switch which may be easily adjusted. Although I have described my device as being responsive to decelerating conditions, it is obvious that my invention is equally responsive to accelerating conditions. While the preferred embodiments of the switch have been illustrated and described in detail, it should be understood that the invention is not limited to these details of construction but that numerous changes may be made without departing from the scope of the following claims.

I claim:

1. In a device of the class described, a member revolvable about an axis, a movable element associated with the revolvable member and movable in a path defined by said member, the movable element being movable responsive to centrifugal force in a path disposed at an angle to a radial plane extending through the axis of the revolvable member and intersecting said path, whereby the movable element is responsive to changes in the speed of the revolvable member.

2. An electric switch, comprising: a rotatable driving member; contact means; controlling means revolvable by said driving member and movable under influence of forces caused by said revolution to control said contact means; means for directing the movement of said controlling means in an inclined path disposed at an angle to a plane passing through said axis of rotation of said driving member and intersecting said path; and means for adjusting said directing means to alter said inclination of the path.

3. An electric switch, comprising: a driving member rotatable about an axis; contact means; and controlling means revolvable by said driving member and movable under influence of forces caused by said revolution to control said contact means, said controlling means being movable in a path intersecting a plane passing through said axis of rotation of said driving member and intersecting said path.

4. An electric switch comprising a driving member rotatable about a fixed axis, contact means, controlling means revolvable by the driving member and concurrently movable under influence of forces caused by said revolution to control the contact means, means constraining the controlling means to a path of movement angularly disposed to the plane which is defined by the axis of the driving member and radius of revolution of the controlling means, and means to adjust the angular disposition of said path with respect to said plane.

5. An electric switch, comprising: a rotatable driving member; contact means; and controlling I means rotatable by said driving member and movable in response to changes in angular velocities of said driving member to operate said contact means, and movable in response to rates of decrease in angular velocity of said driving member to again operate said contact means.

6. In a device of the class described, a member revolvable about an axis, an element movable in a path defined by said member, said element having a normal position and being movable from said normal position responsive to centrifugal force, said path being disposed at an angle to a plane passing through said axis and intersecting said path, the end of said path toward the axis being positioned revolvably in advance of the other end of said path whereby said element is movable towards the axis responsive to decreases in the revolving speed of said member, and a contact controlled by said element.

'7. In a device of the class described, a, member revolvable about a substantially vertical axis, an element movable in a path defined by said memher, said path being disposed at an angle to a plane passing through said axis and intersecting said path whereby said element is responsive to centrifugal force and to changes in the speed of said revolving member, and a contact controlled by said element.

8. In a. device of the class described, a member revolvable about an axis, an element associated with said member and movable in a path defined by said member, said path having the portion thereof remote from said axis positioned higher than and revolvably behind the portion thereof adjacent said axis, and means to adjustably vary the relative positions of the portions of said path both vertically and revolvably.

9. In a device of the class described, a member revolvable about a substantially vertical axis, a movable element associated with said member, the element being movable in an inclined path disposed at an angle to a vertical plane passing through said axis and intersecting said path, and means to vary the inclination of said path and the angle said path makes with said plane, said means comprising a support rotatable about an axis disposed substantially at 45 to said vertical axis, and a second support rotatably supported on said first member and rotatable on an axis extending substantially perpendicular to the axis on which the first support is rotatable, said supports being so arranged with respect to each other that adjusting of said path with respect to one of said supports leaves the adjustment of said path with respect to the other of said supports substantially unaltered.

10. In a device of the class described, a member revolvable about an axis, an element associated with said member and movable in a path defined by said member, said element having a normal position and being movable from said normal position responsive to centrifugal force, the path defined by said member being inclined and disposed at an angle to a plane passing through said axis and intersecting said path, whereby the element is responsive to changes in the speeds of the revolving member, a contact controlled by said element, and means to adjustably vary the amount of inclination of said path.

11. In a device 01' the class described, a member revolvable about an axis,'an element movable in a path defined by said member, said element having a normal position and being movable from said normal position responsive to centrifugal force, said path defined by said member being disposed at an angle to a plane passing through said axis and intersecting said path, whereby the element is responsive to changes in the speeds of the revolving member, a contact controlled by said element, and means to adjustably vary the angle said path-makes with said plane, whereby the effect of changes in speed of the revolving member is adjustably varied.

12. In a device of the class described, a member revolvable about an axis, an element movable in a path defined by said member, said path being inclined and disposed at an angle to a plane passing through said axis and intersecting said path, whereby the element is responsive to centrifugal Iorce and to changes in the speed of the revolving member, a contact controlled by the element, and means to adjustably vary the inclination of said path and the angle said path makes with said plane.

13. In a device of the class described, a member revolvable about a substantially vertical axis, an element movable in a path defined by said member, said path having the portion thereof remote from the axis of said member positioned higher than and revolvably behind the portion thereof adjacent the axis of said member, and means to adjustably vary the relative positions of the portions of said path both vertically and revolvably, whereby an adjustment of either one of said positions does not aflect the adjustment of said other position.

HARRY L. WILCOX.

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