US3141348A

US3141348A - Operating mechanism

Info

Publication number: US3141348A
Application number: US134235A
Authority: US
Inventors: John K Dixon
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1961-08-28
Filing date: 1961-08-28
Publication date: 1964-07-21
Anticipated expiration: 1981-07-21

Description

July 2l, 1964 J. K. DIXON 3,141,348

OPERATING MEcHANIsM July 21, 1964 J. K. DIXON 3,141,348

OPERATING MECHANISM Filed Aug. 28. 1961 2 Sheets-Sheet. 2

United States Patent O 3,141,348 PERATN G MECHANISM .Tohu K. Dixon, Milwaukee, Wis., assigner to Allis- Cvhialmers Manufacturing Company, Milwaukee,

Filed Aug. 28, 1961, Ser. No. 134,235 3 Claims. (Cl. 'i4-425) This invention pertains to an operating mechanism in general and more particularly to an operating mechanism for controlling the ow of elastic fluid through an elastic fluid turbine. A

In certain uses of elastic iiuid turbines, it is necessary to have reserve power available for running the turbine at a faster speed and greater horsepower than is normally required. A particular application of such an arrangement is a steam turbine used on a marine vessel. Most of the time during operation of a ship the steam turbine providing the power for driving the ship will only be required to produce suiiicient power to propel the ship at cruising speed. It is, therefore, desirable to design the steam turbine so that it will be most eicient at the power required to propel the ship at this cruising speed.

In a steam turbine, low ow capacity turbine blading provides more eiiicient rotative power at cruising speed than high flow capacity blading. It is, therefore, common practice to provide two sets of turbine blading, one being of the high capacity type for above cruising operation and another set of turbine blading of low capacity for operation at cruising speed or below.

It is necessary in such an arrangement to provide a steam inlet valve which is selectively positionable to slightly vary the amount of steam to the turbine blading to increase and decrease the horsepower output of the turbine and hence the ship speed. This can quite eiiiciently be accomplished by providing a hand wheel with a worm thereon which drivingly engages a worm wheel connected to the inlet valve and thereby is capable of slight variations in vthe amount of steam admitted to the turbine. By turning the hand wheel the operator can slightly adjust the amount of steam admitted to the turbine and thereby slowly or quickly adjust the speed of the ship up `to cruising speed. However, when it is desired to operate the ship at above cruising speed, it is necessary to bypass the low capacity turbine blading and admit the steam directly to the high capacity blading. It is desirable that this change of steam direction be accomplished quickly. This change in steam direction can be accomplished by providing a bypass valve connecting the steam inlet valve directly with the high capacity turbine blading. It would be desirable if the bypassV valve would automatically open when the operator requires speed above cruising. It would be possible to provide a separate actuating mechanism controlled by the ship operator to open the bypass valve and admit the steam to the high capacity blading. However, it would be more desirable if the same control could be used to both slowly and slightly vary the amount of steam admitted to the turbine and, furthermore, quickly open the bypass valve when cruising speed is to be exceeded without any additional or separate signal from the ships operator.

lt is, therefore, the general intention of the subject invention to provide an operating mechanism which can be used to slowly rotate a shaft and also quickly rotate the shaft.

It is a further object of the subject invention to provide an operating mechanism including a worm drivingly engaging a worm wheel wherein the worm is capable of both rotational and longitudinal movement to drive the worm wheel at different rotational speeds.

A further object of the subject invention is to provide an elastic fluid turbine having low capacity and high capacity elastic uid blading, including a bypass valve selectively positionable to bypass the low capacity blading, with an operating mechanism which is capable of slight adjustment of the amount of elastic fluid admitted to the turbine and also capable of quick operation of the bypass valve.

Another object of the subject invention is to provide an operating mechanism for an elastic fluid turbine of the hereinbefore described type wherein rotation of a worm rotates a worm wheel to control the amount of elastic fluid admitted to the turbine and wherein longitudinal movement of the worm rotates the worm wheel to open the bypass valve to admit elastic uid directly to the high capacity turbine blading.

An additional object of the subject invention is to provide an operating mechanism for an elastic iuid turbine of the hereinbefore described type wherein power means are utilized to longitudinally move `the worm to drive the worm wheel.

A further object of the subject invention is to provide an operating mechanism for an elastic iluid turbine of the hereinbefore described type wherein the power means holds the worm shaft against indiscriminate longitudinal movement and a safety device is provided which is operative to engage the worm shaft and hold same against longitudinal movement in response to a failure of the power means.

These and other objects of the subject invention will become more fully apparent when the following description is read in light of the attached drawing, wherein:

FIGS. 1 through 4 are schematic diagrams of the invention showing the elements thereof in different positions of operation.

Referring to the drawings, and particularly FIG. 1, a main steam inlet valve generally designated 11 is shown in a partially opened position. Steam from a source (not shown) is admitted to a steam chest 12 through a steam inlet 13. A series of valve seats 14 are provided in the lower wall of the inlet valve and these valve seats when opened permit steam to enter a turbine inlet pipe 16. This pipe is connected to the inlet of a turbine generally designated 17. The turbine has a spindle 18 to which are connected three sets of

turbine blades

19, 21 and 22. The turbine blade set 19 is a pilot set of blades upon which all of the steam impinges. The set of blades 21 are low capacity blading which will only pass a limited amount of steam therethrough. The blades 21 will cause the turbine to develop a predetermined horsepower, however, as additional steam is admitted to these blades, the horsepower output of the turbine will not increase as the additional steam cannot pass through the blading. The set of turbine blading 22. is of the high capacity type and all of the steam which can be admitted to the turbine can pass therethrough to increase the horsepower output of the turbine. As the steam expands through the blade set 22, it passes through an exhaust or cross over pipe 23 and may then be directed to a lower pressure turbine (not shown).

As herein shown, a bypass valve 24 may be integrally connected to the turbine 17. This bypass valve may include two

valve seats

26 and 27 and longitudinally

reciprocable valves

28 and 29 which are movable to close and open the

valve seats

26 and 27, respectively. An inlet chamber 31 of the bypass valve 24 is in steam communication with Vthe turbine 17 on the upstream side of the low capacity blading 21. An exhaust port 32 in the bypass valve is in steam communication with a turbine charnber 36 on the downstream side of the low capacity turbine blading and on the upstream side of the high capacity turbine blading 22. In this manner when the bypass valve 2? is open, steam is permitted to pass through the valve seat 26 and through the exhaust port 32 and impinge 3 directly on the high capacity turbine blading 22. Although two partially pressure balanced valves are herein shown because of the high pressures involved, it would be understood that a single valve would suice in many instances. In the embodiment shown, a conduit 30 directs the steam passing through seat 27 to port 32.

The bypass valve 24 may be operated in any conventional manner and is herein shown as having a valve stern 33 extending into operative engagement with a bifurcated end of a plunger 34. The plunger 34 may be reciprocably received in a bore 36 provided in one end of the bypass valve 24. The valve stem 33 may be provided with an annular shoulder 37 against which one end of a spring 38 is seated. The other end of the spring 38 is seated against one wall of the plunger 34. In this manner, the valve stem 33 and the connected

valves

28 and 29 are biased by means of the spring 38 into seating engagement with the

valve seats

26 and 27 and thereby close the bypass valve to passage of steam. The plunger 34 may be provided with a flange 39 on the bifurcated end thereof which is capable upon movement in a right hand direction, as viewed in FIG. 1, to contact the shoulder 37 and move the valve stern 33 to the right. This results in a right hand movement of the

valves

28 and 29 opening the

valve seats

26 and 27 and permitting steam to iiow therethrough. When the plunger 34 is moved to the left, the valve stem follows this movement due to the urging of the spring 33.

The plunger 34 may be moved in any manner and is herein shown for purposes of illustration as having two

cam follower rollers

41 and 42 attached thereto. A cam 43 in operative engagement with both the

followers

41 and 42 is rotatable to move the plunger 34 in either the left or the right hand direction.

The inlet valve 11 may be constructed in any conventional manner so as to vary the amount of steam admitted to the turbine and is herein shown for purposes of illustration as being provided with a number of valves 46 for selective cooperative engagement with the valve seats 14. As can be seen in FIGS. l and 2, the valves 46 have stems 47 of varying lengths. The valve stems 47 pass through a lift bar 48. Each valve stem has a shoulder 49 thereon which is engaged by the lift bar 48 as it is moved upwards. Due to the different lengths of the valve stems 47 as the lift bar 48 is moved upward the individual valves are lifted at different times as the lift bar engages the shoulders 49. Suction caused by the steam passing through the valve 11 and gravity cause the valves to reseat as the bar 48 is lowered.

The lift bar 43 may be moved in any convenient manner and is herein shown as being connected to a longitudinally disposed link 51 by means of

rods

52 and 53 which are pivotally connected to the outer ends of the link 51. The link 51 is pivotally connected to an additional link 54 which is pivotally connected to one end of a lever 56. The lever 56 is fulcrumed on a support 57 intermediate the ends thereof and has its other end bifurcated and provided with two cam follower rollers 58 and 59. The cam follower rollers 5S and 59 operatively engage a cam 61 which is eccentrically connected to a drive shaft 62. Rigidly connected in -any conventional manner to one end of the drive shaft 62 is a worm wheel 63. As can best be seen in FIGS. 3 and 4, the drive shaft 62 extends beyond the worm wheel 63 and a wheel 64 is attached thereto. The wheel 64 has two circumferentially spaced protuberances 66 and 67 on the periphery thereof. Both the worm wheel 63 and wheel 64 are connected to the drive shaft 62 for rotation therewith. The other end of the drive shaft 62 may be provided with a bevel gear 63 which is drivingly engaged with an additional bevel gear 69 which is connected for rotation with the cam shaft 44.

The worm wheel 63 may be journaled for rotation in a cylindrical housing '71 which may be integrally formed with a worm housing 72. The worm housing 72 has a worm shaft 73 journaled for rotation therein to which is rigidly connected a worm 74 drivingly engaging the worm wheel 63. The worm shaft 73, as viewed in FIG. 1, extends upward without the worm housing 72 and may be provided with an internally splined portion 76 into which is received a splined section of a shaft 77 to which may be connected a hand wheel 78. Support means 79 may be provided in any conventional manner to permit rotation of the shaft 77 while resisting longitudinal movement thereof. The splines on

theshafts

73 and 77 permit longitudinal movement of the worm shaft 73 relative to the hand wheel shaft 77.

As viewed in FIG. 1, the lower portion of the worm housing 72 may be formed to provide a power cylinder 31. Reciprocably contained within the power cylinder 01 is a piston 82. Attached to the piston for movement therewith is a shaft 83. The upper end of shaft 83 may be provided with threaded portion 34 for connection to a piston 86 which is reciprocably received within the worm housing 72. The lower end of worm shaft 73 may be of reduced diameter and may have an annular shoulder 87 thereon. This shoulder is contained in a cylindrical recess 8S in the piston 86. This connection permits relative rotation between the piston rod 83 and the worm shaft 73, while resisting relative longitudinal movement therebetween.

In the event of a failure of the power cylinder 81, to hold the worm shaft 73 against longitudinal movement, a safety means generally designated 89 is provided. The safety means may be supported in any conventional manner and is herein shown for purposes of illustration as having a housing which is formed integrally with the worm housing 72. A cylindrical chamber 91 in the safety means housing slidably receives a piston 92 which is rigidly connected to one end of a piston rod 93. The other end of the piston rod 93 is contained in a bore which is open to the interior of worm housing 72. A spring 94 seated between the left hand end (as shown in FIG. 1) of the safety means housing 89 and the piston 92 biases the piston rod 93 towards the worm housing 72. When the piston rod is permitted to move into the worm housing, it will either-be above or below the piston 86. The piston 86 will be held against longitudinal movement between the rod 93 and either a lower wall 96 of the worm housing or an annular flange 97 provided on the inner periphery of the worm housing 72.

A pressure fluid supply` line 98 delivers pressurized uid from a source (not shown) to the safety means chamber 91 through a conduit 99, to a main control valve 101 through an inlet port 102 and to a pilot valve 103 through a conduit 104. In this manner it can be seen that pressurized fluid is continually acting on the piston 92 of the safety means 89 thereby overcoming the urging of the spring 94 and withholding the rod 93 from entering the worm housing 72.

Pressurized fluid is furthermore continually acting on the pilot valve 103. This valve may comprise a cylindrical housing 106 which is divided into three

uid chambers

107, 108 and 109. Valve seats 111 and 112 are provided between these chambers. Reciprocably contained within the valve housing 106 is a valve stern 113 having

valves

114 and 116 attached thereto. The

valves

114 and 116 are positioned for operative engagement with the valve seats 111 and 112, respectively. A spring 117 seated against one end of the valve housing 106 and against the valve 114 biases the

valves

114 and 116 to a position to close the valve 114 and open the valve 116 as shown in FIG. 1. The valve stem 113 extends without the valve housing 106 and is in abutting engagement with a lever 118 which is pivotally connected to the valve housing 106. As shown in FIG. 1, a cam follower roller 119 is rotatably connected to the lever 118 and is operatively engaged with the wheel 64 connected to the main drive shaft 62.

A conduit 121 in fluid communication with the fluid chamber 108 of pilot valve 103 is also in fluid communication with the main control valve 101. Positioned in the conduit 121 is a conventional check Valve 122 Which permits ow of fluid from the pilot valve 103 to the main control valve, however, blocks the flow of fluid in the reverse direction.

An additional pilot valve 123 similar to the pilot valve 103 is provided with a cylindrical housing divided into two fluid chambers 124 and 126. The center wall of the pilot valve 123 has a valve seat therein. A valve 127 is reciprocably received in the pilot valve 123 for operative engagement with the valve seat and is connected to a valve Stem 128 which extends without the pilot valve housing and is positioned for abutting engagement with a lever 129. A spring 131 biases the valve 127 into a closed position to block the ow of fluid between the chambers 124 and 126. The lever 129 is pivotally connected to the pilot valve 123 and is provided at one end thereof with a cam follower roller 132. The cam follower roller 132 is in operative engagement with the wheel 64. A conduit 133 connects the iluid chamber 124 in uid communication with the conduit 121 in downstream relation to the check valve 122.

Referring to FIGS. 3 and 4, the main control valve 101, shown herein for purposes of illustration, includes two longitudinally

reciprocable piston rods

134 and 136. The piston rods are supported for longitudinal movement within the control valve 101. The piston rod 134 has two longitudinally spaced pistons 137 and 138 thereon. Piston 137 is slidably contained within a fluid chamber 139 and piston 138 is slidably contained Within a fluid chamber 141. The two chambers 139 and 141 are connected together in iluid communication by the passage 142 and an additional chamber 143 is connected in uid communication to chamber 139 by passage 144.

Piston rod 136 has two pistons 146 and 147 connected thereto. Piston 146 is slidably contained in a chamber 148 and piston 147 is slidably contained in an additional chamber 149.

Chambers

148 and 149 are connected in uid communication by the passage 151. Chambers 143 and 148 are connected in fluid communication by the passage 152. Additional chambers 141 and 149 are connected in iiuid communication by the passage 153. Each of the

piston rods

134 and 136 and the attached pistons are biased to the right as viewed in FIGS. 3 and 4 by

springs

154 and 156, respectively.

The chamber 139 is connected in fluid communication with the upper end of power cylinder 81 by means of a conduit 158. The lower end of power cylinder 81 is connected in fluid communication with the passage 151 by means of conduit 159. Pressurized fluid in conduit 98 is delivered to chamber 148 through the inlet port 102 and discharge uid from chamber 141 is directed to a sump (not shown) by means of conduit 161.

The operation of the subject invention will now be described by referring rst to FIG. 1. Assuming that the ships operator wishes to increase the speed from below cruising to cruising speed, the hand wheel 78 is turned in a counterclockwise direction causing the worm 74 to rotate the worm wheel 63 in a clockwise direction forcing the cam 61 to pivot the lever 56 in a counterclockwise direction about the fulcrum support 57. This causes the lift bar 48 to move upward increasing the number of valves 46 removed from their coacting seats 14. As this occurs, more steam from the chamber 12 passes through the valve seats and acts on the

turbine blades

19, 21 and 22 causing the turbine and hence the ship to move at a greater speed. As the operator continues to turn the hand wheel, more valves are lifted from their respective seats and more steam is directed to the turbine to increase the speed of the ship. As the worm wheel 63 rotates, the main drive Shaft 62 causes the bevel gear 68 to rotate and hence, due to the bevel gear connection with the shaft 44, causes the cam 43 to also rotate. The profile of the cam 43 is such that the plunger 34 does not move to unseat the

valves

28 and 29 of the bypass valve 24 until the protuberances 66 and 67 contact the pilot valves

cam follower rollers

119 and 132.

When it is desired to increase the speed of the Ship above cruising speed, the operator continues to rotate the hand wheel 78 in a counterclockwise direction. The worm wheel 63 is rotated to the point where the protuberances 66 and 67 contact the

cam follower rollers

119 and 132. The lever 129 is pivoted out of contact with the valve stem 128 and hence has no effect on the position of valve 127 which remains closed. However, lever 118 is pivoted into engagement with valve stem 113 and forces valve 114 from its seat while moving valve 116V into engagement with its seat. At this point pressurized fluid in the conduit 104 passes through the valve seat 111 and into the conduit 121 passing through the check valve 122 into the main control valve 101. The resultant force of this uid acting upon the pistons 138 and 147 (FIG. 3) causes both

piston rods

134 and 136 and the attached pistons to move to the left against the urging of

springs

154 and 156. Pressurized uid is then permitted to pass from chamber 148 into the passageway 151 through the conduit 159 into the lower portion of the power cylinder 81 and move the piston 82 upward. Since the worm shaft 73 is connected for longitudinal movement with the piston 82, upward movement of piston 82 causes upward movement of Worm 74 causing a faster rotation of worm Wheel 63. As Worm Wheel 63 is rotated as a result of longitudinal movement of worm '74, the drive shaft 62 rotates cam shaft 44 and causes faster rotation of the cam 43. Because of the profile of cam 43, this rotation causes a larger radius surface of the cam to act on the cam follower roller 42 forcing the plunger 34 to the right and causing the flange 39 to contact the shoulder 37 formed on the bypass valve piston rod 33. The

bypass valves

28 and 29 are thus removed from their

seats

26 and 27 and the steam in conduit 16 is permitted to pass through the bypass valve directly into chamber 25 and to impinge on the high capacity turbine blading 22. Due to the profile of cam 61, the position of valves 46 remains constant while the bypass valve is being opened.

Although not shown, the profile of cam 43 is such that the

bypass valves

28 and 29 are slightly opened before the protuberances 66 and 67 Contact the

cam follower rollers

119 and 132. In this manner the bypass valve 24 permits a throttling of steam through the bypass valve to impinge directly on the high capacity turbine blading and thereby insure a smooth increase in speed from cruising to above cruising operation.

Once the bypass valve has been opened, continued counterclockwise rotation of the hand wheel '78 will open additional inlet valves 46 to permit more steam to impinge directly on the high capacity turbine blading through the bypass valve 24.

When it is desired to decrease the speed of the turbine, the hand wheel '78 is turned in a clockwise direction causing the worm wheel 63 to rotate in a counterclockwise direction as indicated in FIG. 4. As the protuberances 66 and 67 contact the

cam followers

119 and 132, lever 118 is rocked out of engagement with valve stem 113 permitting spring 117 to close the valve 114 blocking conduit 104 from conduit 121 and valve 116 is unseated permitting fluid in the conduit 121 above the check valve 122 to pass through valve seat 112 and return to sump (not shown) through a return conduit 162.

When protuberance 67 contacts cam follower roller 132, the lever 129 is caused to engage valve stem 128 removing valve 127 from its seat. This permits fluid in the conduit 121 downstream of the check valve 122 to pass through the valve 123 and return to sump (not shown) through an exhaust conduit 163. At this point pressurized fluid is drained from the right hand end of main control valve 101 and due to the urging of

springs

154 and 156 the

piston rods

134 and 136 and the attached pistons move to the right. Pressurized lluid in conduit 98 then passes through chamber 143 by way of passage 14E-ft into chamber 139. From chamber 139 the fluid passes through conduit into the upper portion of power cylinder S1. Pressurized fluid in the upper portion of cylinder 81 forces piston h2 downward urging duid from the lower portion of the power cylinder through conduit 159 into chamber 149 through passage 151. From chamber 149 the fluid passes through passage 153 into chamber M1 and out through the exhaust conduit 161 to the sump (not shown).

As the piston 82 moves downward, the worm shaft 7.3 also moves downward causing the worm to rotate the worm wheel in a counterclockwise direction. Counterclockwise rotation of worm wheel 63 causes the drive shaft 62 to rotate the shaft 4d and the attached cam 43 in a counterclockwise direction moving plunger 3d to the left and permitting the spring 3S to ciose the bypass valve 24. When the protuberances 66 and e7 pass beyond the

cam follower roller

119 and 132, respectively, they have returned to the position shown in FIG. 1 and the turbine is again operating at or below cruising speed.

In the event of a failure of the power means, the worm wheel 63 might offer sufiicient resistance to rotation of the worm 74 so that the worm shaft 73 would merely move in a longitudinal direction rather than rotate the worm wheel. It is, therefore, desirable to provide an emergency device wherein the Worm shaft 73 is held against longitudinal movement in the event of a failure of the power system. To provide for the possibility of a failure of the power system, the piston 92 is held in a disengaged position due to the pressure duid acting on the right hand side of the piston. If there should be a failure of the power system, the spring 9d will cause the piston rod 93 to move to the right into the worm housing 72. above or below the piston S6 and thereby hold the worm shaft against longitudinal movement while permitting rotational movement thereof. The bypass valve 24 may be opened and closed without the use of the power cylinder 81, however, a considerable number of additional rotations of the hand wheel '7d would he required.

While only one embodiment of the subiect invention has been shown and described herein, it will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the invention or from the scope of the appended claims.

What is claimed is:

1. An operating mechanism comprising: a support; a rst shaft rotatably supported by said support; a worm wheel connected to said first shaft for rotation therewith; a second shaft supported by said support, said second shaft being capable of both rotational and longitudinal movement; a worm connected to said second shaft for movement therewith and drivingly engaging said worm Wheel;

CII

control means connected to said second shaft forrotating same; power means engaging said second shaft and resisting longitudinal movement thereof, said power means being responsive to a predeterminedrotated position of said control means to longitudinally move said second shaft to cause said first shaft to rotate a predetermined amount.

2. An operating mechanismcornprising: a support; a first shaft rotatably supported by said support; a worm wheel connected to said first shaft for rotation therewith; a second shaft supported by said support, said second shaft being capable of both rotational and longitudinal movement; a worm connected to said second shaft for movement therewith and drivingly engaging said worm wheel; power means engaging said second shaft and resisting longitudinal movement thereof, said power means being responsive to a predetermined rotated position of said first shaft to longitudinally move said second shaft to cause said first shaft to rotate a predetermined amount; safety means positioned for selective engagement with said operating mechanism to hold said second shaft against longitudinal movement, said safety means being responsive toa failure of said power means to engage said second shaft, and control means connected to said second shaft for rotating same.

3. An operating mechanism comprising: a support; a first shaft rotatably supported by said support; a worm wheel connected to said first shaft for rotation therewith; a second shaft supported by said support, said second shaft being capable of both rotational and longitudinal movement; aworm connected to said second shaft for movement therewith and drivingly engaging said worm wheel; control means for rotating said second shaft; means rotatably connecting said control means to said second v shaft, said means permitting longitudinal movement of said second shaft relative to said control means; power means engaging said second shaft and resisting longitudinal movement thereof, said power means being responsive to a predetermined rotated position of said control means to longitudinally move said second shaft to cause said first shaft to rotate a predetermined amount.

References Cited in the le of this patent UNITED STATES PATENTS 1,117,306 Banner Nov. 17, 1914 1,223,342 London Apr. 17, 1917 v1,385,970 Norton July 26, 1921 1,387,636 Alden Aug. 16, 1921 1,476,801 Dahlstrand Dec. 11, 1923 2,793,630 Halik May 28, 1957 2,903,894 Legros Sept. 15, 1959 3,012,448 Abraham Dec. 12, 1961

Claims

1. AN OPERATING MECHANISM COMPRISING: A SUPPORT; A FIRST SHAFT ROTATABLY SUPPORTED BY SAID SUPPORT; A WORM WHEEL CONNECTED TO SAID FIRST SHAFT FOR ROTATION THEREWITH; A SECOND SHAFT SUPPORTED BY SAID SUPPORT, SAID SECOND SHAFT BEING CAPABLE OF BOTH ROTATIONAL AND LONGITUDINAL MOVEMENT; A WORM CONNECTED TO SAID SECOND SHAFT FOR MOVEMENT THEREWITH AND DRIVINGLY ENGAGING SAID WORM WHEEL; CONTROL MEANS CONNECTED TO SAID SECOND SHAFT FOR ROTATING SAME; POWER MEANS ENGAGING SAID SECOND SHAFT AND RESISTING LONGITUDINAL MOVEMENT THEREOF, SAID POWER MEANS BEING RESPONSIVE TO A PREDETERMINED ROTATED POSITION OF SAID CONTROL MEANS TO LONGITUDINALLY MOVE SAID SECOND SHAFT TO CAUSE SAID FIRST SHAFT TO ROTATE A PREDETERMINED AMOUNT.