US3651741A - Saw mill feedworks - Google Patents

Abstract

A feedworks for sawmills incorporating structure for converting steam systems to water-drive systems and, irrespective of the type of drive system employed, including means for interrupting or metering fluid-flow in the feedworks for stopping or at least slowing down the feedworks'' carriage when traveling at an excessive speed proximate its extremity of travel, as a safety feature.

Description

Elite tats e11 Sylvester 1 Mar. 28, 1972 [54] SAW M11911 FEEDWQRKS 2,922,439 1/1960 Palmer ..91/405 3,216,444 11/1965 Herner. [72] invent James Sylvester Salt Lake Utah 3,272,083 9/1966 Stoll ..91/405 [73] Assignee: Gardner Machines, lnc., Salt Lake City, 3,440,932 4/1969 Gutnikov et a1. ..91/435 Utah [22] Filed, May 11, 1970 Primary Examiner-Paul E. Maslousky Attorney-M. Ralph Shaffer [2]] Appl. No.: 36,105

[57] ABSTRACT [52] US. Cl ..91/435, 91/459, 91/466 A feedworks for Sawmills incorporating Structure for c0nven [51] m- Cl Flsb 111/04 F1513 13/044 ing steam systems to water-drive systems and, irrespective of Field 01 Search 1/406, 405, 435, 459, 466 the yp of drive System employed, including means for nap rupting or metering fluid-flowin the feedworks for stopping or [56] References clued at least slowing down the feedworks carriage when traveling UNITED STATES PATENTS at an excessive speed proximate its extremity of travel, as a safety feature. 2,158,060 5/1939 Alden ..91/406 2,871,830 2/1959 Wirth et al ..91/435 8 Claims, 9 Drawing Figures PATENTEDMAR28 I972 SHEET 1 OF 2 INENTOR James Lyivesier His Aimme PATENTEDMAR28 1912 SHEET 2 BF 2 JFIG. 6

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INVENTUR. James LSyIvesfer His Attorney JFIQB SAW MILL FEEDWORKS This invention relates to feedworks for sawmills, and more particularly, to improvements in feedworks wherein an automatic safety feature is incorporated whereby carriage travel may be slowed down and/or stopped at extremities of its travel in the event of power failure, malfunction, or inattention by the operator; the invention also includes means for converting conventional steam systems to water-drive systems.

In the past, a number of different types of feedwork for sawmills have been developed. Conventional systems incorporate a steam drive for reciprocating the log carriage and reciprocating rod thereof along a course of travel, this for cutting a log in rough planks according to the manipulation of carriage structure. In steam systems there are a number of disadvantages including the requirement of fuel and boiler apparatus to heat water to steam temperature, gasket sealing, and the compressible nature of steam which detracts from the feature of a steady positive drive.

In the present invention the conventional steam system is converted to a water-drive system wherein, by virtue of the noncompressible nature of water, a positive fast-acting response is had relative to carriage travel upon manipulation of the associated controls. Further, the requirement of fuel and steam boilers is eliminated.

An additional prior difficulty has been the problem of the danger presented when heavy reciprocating masses are involved, as in feedworks. It is believed most important to supply in a feedworks, whether steam or water driven, a suitable safety feature whereby, at at least the outermost extremity of travel, there is some automatic means for slowing down or stopping the carriage in its travel if it is going at an excessive rate ofspeed at such point.

In the present invention, not only is provision made for converting a steam system to a water drive system, but also the feedworks, of whatever nature, is supplied with a structural safety provision whereby, where carriage travel is excessive proximate its outermost extremity of travel, for example, automatic control means come into play to reduce or even to shut off fluid-flow in feedworks circuit, thereby affecting advantageously the fluid drive of the carriage.

Accordingly, the principal object of the present invention is to provide an improved feedworks for sawmills.

An additional object is to provide in a sawmill feedworks certain operating improvements.

An additional object is to provide structural means for converting a steam system to a fluid-drive system in a sawmill feedworks.

An additional object of the present invention is to provide structural means as a safety feature whereby, at least at one extremity of carriage travel, or proximate such extremity, means is supplied for automatically slowing down and/or stopping a carriage traveling at an excessive speed.

A further object of the invention is to provide a safety feature whereby, in the event of malfunction, operator inattention, power failure, the carriage is automatically stopped or slowed down in the event ofsuccessive travel speeds thereof.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings in which:

FIG. 1 is a plan view of a steam-driven feedworks system as to its basic operating essentials, the detailed carriage mechanisms not being shown since the same forms no part of the present invention.

FIG. 2 is a plan view similar to FIG. I, but illustrates the system of FIG. I as being converted from steam-drive to water-drive; the system shown in FIG. 2 is illustrated in fragmentary view and incorporates valve and valve shut-off structural provisions.

FIG. 3 is a fragmentary transverse section taken along the line 3-3 in FIG. 2.

FIG. 4 is a fragmentary front elevation of the left-hand portion of the system wherein the carriage approaches an outermost extremity of travel, the embodiment of a portion of the safety feature incorporated in the invention being shown.

FIG. 5 is similar to FIG. 4 but illustrates another component which can be used in assisting to slow down or stop the carriage at its outermost extremity in travel.

FIG. 6 is a diagrammatic view in schematic form of a pneumatic and electronic safety system for slowing down or stopping the carriage of the feedwork at an extremity of travel thereof.

FIG. 6A is a diagram of various waveforms occuring at portions at the circuit part of FIG. 6, in the event of certain conditions happening.

FIG. 6B is a diagram of the lower portion of FIG. 6 wherein the control valve condition has been reversed.

FIG. 7 is a view of an alternate safety system wherein a pressure-operated pneumatic switch means is incorporated in shutting off or metering fluid flow in the feedwork system in the event of excessive carriage speed at its extremity of travel.

In FIG. 1 feedworks cylinder 10 is made up of a plurality of sections 11-14 which are bolted or otherwise secured together at their end flanges in the manner illustrated. Sections 11 and 14 include suitable ports 15 and 16 on the underside thereof for receiving the respective ends 17 and 18 of conduit 19 and 20, respectively. Conduit 19 and 20 are routed, as shown by respective dotted lines 21 and 22, to a conventional steam supply and control system 23 which is standard in the art. Section 1 1 includes an end fitting 24 which is supplied with ajournaling bore 25 and contained journal packing 26, this for journaling piston rod 27 of the feedworks. The piston rod 27 is provided with a piston 28 in conventional manner as shown in dotted line configuration in FIG. 1.

Piston rod 27 is connected to carriage 28 in any usual manner, see FIG. 4. Carriage 28 is shown in FIG. I in abbreviated form, the bed 29 and wheels 30 journaled thereto being illustrated. The remainder of the carriage structure as, for example, the log manipulating and control apparatus is deleted for purposes of clarity and forms no part of this invention.

It is seen in FIG. 1 that the feedworks therein shown, a steam-type gun," includes an end flange 30 which is bolted or otherwise secured to flange 31 of Section 14. When it is desired to modify the equipment so that a water-type system is provided, then this flange 30 is removed and replaced by a 180 elbow 32, see FIG. 2. The latter is bolted or otherwise secured to the flange 31 as shown in FIG. 2. The structure 24 of FIG. I is then removed and replaced by a suitable custom fitting or structural equivalent in the form of a tee 33. The latter includes an arcuate leg extremity 34 which is bolted to the flange 35 of valve 36. Valve 36 includes a flange 37 which is bolted to flange 38 of cylindrical section 39. Cylindrical section 39 is joined by a elbow 40 to composite valve control and reservoir unit 41 which is actuated by control unit 42. Units 41 and 42 may be conventional in form, form in themselves no part of the present invention, and utilize the structure illustrated in U.S. Pat. Nos. 3,049,147 and 3,168,854, assigned to the assignee of the present invention, and incorporated fully herein by way of reference.

Continuing, elbow 42 is bolted between unit 41 and cylindrical section 43. The latter is joined at its flange 44 to flange 45 of elbow 32.

FIG. 3 illustrates in section of the valve 36 which may take the form of a plug valve as indicated by the gate 46 rotatably disposed in gate seat 47. Valve gate 46 includes integral shaft 48, the latter being provided with pinion 49. Pinion 49 meshes with rack gear 50, and the latter is pinned by suitable means 51 to control piston rod 52 of pressure cylinder 91. The control piston rod 52 is shown in diagrammatic form in FIGS. 6 and 7, by the way of example.

As in conventional practice, the carriage 28, see FIGS. 4 and 5, conventionally rolls upon tracks 53 and 54, and may be provided with a pneumatic bumper stop 55 of conventional form (see FIG. 5), or can be supplied with an electrical limit stop system including platform 56 and limit switches 57 and 58 disposed thereon. The limit switches 57 and 58 will be conventional in form, having switch arms 59 and 60 provided with rollers 61 and 62 and compression springs 63 and 64. The limit switches 57 and 58 are normally open type which close upon the respective depression of their respective switch arms, as shown in connection with switch S7 in FIG. 6.

In FIG. 6 a schematic diagram of a representative valve actuating system is illustrated. Alternating current input plug 57' is connected by leads 58 and 59 to an AC-to-DC converter 60 the output side of which is grounded or maintained in a common reference potential 61. The positive side of converter 60 is connected by leads 62 and 63 to respective terminals of limit switches 57 and 58, respectively. The remaining terminals of switches 57 and 58 are respectively connected to conventional, unistable multivibrator MVI and multivibrator MV2 in the manner illustrated. The remaining input terminals are maintained at said common reference potential. The output of each of the multivibrators MVl and MV2 is coupled through respective coupling capacitors 64 and 65 to a common reference juncture 66 leading into the input side of trigger T. Trigger T is connected by lead 67 to relay winding 68 of relay 69, the remaining winding terminal of which is grounded, and relay arm 70 and relay contact 71 are respectively connected to solenoid 72 and positive electrical supply terminal 73. The remaining terminal of solenoid 72 is connected by lead 74 back to relay arm 70 of relay 69. Solenoid 72 includes a solenoid plunger 75, which withdraws inwardly when the solenoid 72 is energized and which is urged outwardly by compression spring 76 operating against plunger reaction means 77 when the solenoid is not in its energized state. As shown in FIG. 6, the solenoid 72 is a DC solenoid which is energized by virtue of the positive and negative terminals 73 and 78 being directly connected to the solenoid 72 through relay arm 70. Thus, in the present condition shown the four-way valve 79 is in normal position, that is, in its regular operating condition during regular use of the feedworks. Control valve 79 may include an outer cylindrical housing 80 and an inner spool 81, the former being provided with valve apertures 82-87 and the latter being supplied with spool apertures 88-90.

Before the operation of the valve is described it is best to point out that a control cylinder 91 includes cylinder member 92 journaling piston 93. The latter is connected to the piston rod 52, previously described, which actuates rack gear 50. The latter meshes with pinion 49 which is keyed to the valve 36.

Control cylinder 91 is a double-acting cylinder having respective lines 94 and 95 engaging the ports 86 and 87 of valve 79 in the manner illustrated.

The consideration of the right-hand portion of FIG. 6 as to operation will now be made. In the normal condition, as hereinafter explained, relay 69 will not be energized.

Accordingly, solenoid 72 remains in an energized state, being coupled to positive and negative terminals 73 and 78 via relay arm 70 which now is closed. Thus, solenoid 72 is shown in FIG. 6 in its energized state, at which point the valve spool aperture 90 provides communication between ports 85 and 87. This provides for exhaust to the atmosphere. It is noted that valve spool port 89 provides communication between ports 83 and 86 so that air under pressure from compressor C is communicated through line 94 to the left-hand side of control cylinder 91. This operates to urge piston 93 to the right so as to advance rack gear 50 to the right and thus revolve pinion 49 in a clockwise direction, so as to render the valve 36 in open condition. Kindly note the arcuate arrow 0 in FIG. 6.

Suppose, however, that the valve is to be suddenly closed, this because of the fact that through negligence or inadvertence of the operator, the carriage 28 is traveling too rapidly in the direction to the left. In such event, limit switch 58 will be initially closed by the travel thereover of the underside of carriage 28, and this will be followed in close succession by a subsequent closure oflimit switch 57. Again, see FIG. 4. Multivibrator MVl will be chosen such that an initiating pulse, as for example by the closure of limit switch 58, will produce an output pulse of predetermined width, see pulse P1 in FIG. 6. Now, if limit switch 57 is also closed in a very short space of time, that is in a time less than the time duration of pulse P1, then the output pulse P2 of multivibrator MV2 will occur which will be additive relative to the positive pulse P1, this to produce a pulse waveform P3 in FIG. 6. Since the effect is cumulative, then the threshold 1 of trigger T, such as a thyratron tube stage, will be exceeded so that trigger stage T will fire to energize the relay winding 68 of relay 69. This will produce an immediate fall of relay arm from contact 71 so that the potential difference supplied to solenoid 72 is removed. This action causes a forward advancement, that is, to the right, of solenoid plunger and hence of valve spool 81, such that aperture 88 now provides a communication between ports 82 and 86, whereas aperture 89 will provide communication between ports 84 and 87. Such results in a reversal of pressure fluid to the cylinder 91 so that the piston 93 will be urged to the left, see FIG. 6B. This results in a leftward movement of rack gear 50 and a consequent counter-revolvement, see arrow C, of valve pinion 49 to close valve 36. The revolvement of the pinion, of course, revolves the valve plug 46 in the opposite direction so that a closed or essentially closed condition of the valve is achieved. Valve closure will result in an immediate stop in the outwardly traveling carriage and reciprocating piston rod 27. If desired, the valve can have a metering aperture or simply be provided with a structure such that a metered closing (or slight opening) of the valve exists when the limit switches have been operated in the manner hereinbefore described. It is preferable that the carriage come, not to a dead stop, by virtue of the safety system of the invention, but rather that there simply be a slowing down of the unit to call the attention to the operator that a dangerous condition exists.

If the carriage 28, at its extremity of travel proximate the limit switch 51 in FIG. 4, travels at rate of speed which is slower than the pulse width of pulse P1, then the generated pulse F2 from multivibrator MV2 will occur after the time of occurrence of the trailing edge of pulse P1, in which event there will be no additive effect as is shown at composite pulse P3. This then will not serve to trigger the trigger I since the threshold 1 of the latter will not have been exceeded by the input pulse thereto. In such event the relay 69 remains nonactivated and arm 70 will continue to contact relay terminal 71.

FIG. 6A illustrates in enlarged diagrammatic form the pulses or waveforms Pl-P3 as referenced in FIG. 6. FIG. 6B illustrates the position wherein the relay 69 is energized in a manner heretofore described such as to disconnect arm 70 from relay contact 71. Again, clockwise revolvement ofpinion 49 produces an opening of valve 36 whereas a counterclockwise revolveinent of pinion 49 in the direction of the arcuate arrow C, as accomplished by the leftward movement of rack gear 50, will produce a closing actual or metered of the corresponding valve 36.

At this point it is to be mentioned that in the embodiment and condition of FIG. 6 the cylinder is vented to the outside atmosphere via port 85. In FIG. 6B venting takes place via aperture 88 through port 82.

FIG. 7 represents a slightly different embodiment of the invention, but with the system portion R being identical to the corresponding system portion shown in FIG. 6. Likewise, its nature ofoperation will be identical.

In FIG. 7 a bumper unit 96, which may comprise the device 55in FIG. 5, includes a rod 97 terminating at one extremity in a rounded bumper end 98 and at the remaining extremity as a pneumatic piston 99. Pneumatic piston 99 is disposed within cylinder 100. The same is provided with a base 101 which is apertured at 102 approximate the cup configured switch arm 103 of limit switch 104. The terminals of the latter are connected by leads 105 and 106 to relay winding 107 and also to input AC plug 108 in the manner indicated. The remaining 101029 man side of the input plug 108 is grounded, as shown. Likewise, the remaining side of relay winding 107 is maintained at ground or common reference potential. In addition to being provided with relay winding 107, the relay 109 includes the arm 70 and contact 71, corresponding to relay 69 shown in FIG. 6.

In operation relative to FIG. 7, a rapid bump caused by the high-velocity travel of carriage 28 will depress rod 97 and hence piston 99 so that there is a rapid exhaust of air through apertures 102 and V. This in turn produces a depression of the switch arm 103 of normally open switch 104. Such depression serves to energize relay 109 so as to pull downwardly arm 70 and hence disconnect solenoid 72 from its source of power. This results in an outward extension of valve spool 81 so as ultimately, and in the manner shown and described relative to HO. 6, close the valve 36 operatively associated with pinion 49.

Where the travel of the carriage 28 is below a predetermined minimum, then the switch 104 will not be activated since the air pressure proceeding through aperture 102 will be insufficient to depress switch arm 103. A suitable compression spring 109 will be provided in the bumper device 96 so as to abut the rounded end 98 of rod 97 and hence provide an outer restoring force for piston 99 when the carriage is removed from contact therefrom.

It is noted that there is provided a brief closing of the valve in the case of an emergency condition. The same effect will obtain when electrical power fails at the feedworks site. Of course, a complete closing down rather than an intermittent interruption of fluid through the conduit including cylindrical section 39 is possible, as by choosing a bistable relay for relay 169 or 109. Generally, a brief interruption will be sufficient, in most instances, for the operator to be alerted and to actuate the equipment appropriately. Further, relays 69 and 109 may be time-delay relays, if desired. Again, a bistable relay can be employed in lieu of relay 69 where it is intended that the line remain closed for a period of time.

Accordingly, the present invention has provided, firstly, a system for modifying conventional steam-type feedworks for a more modern water-type feedworks where the necessity of steam and fuel is avoided and, secondly, provides a feedworks systems wherein a rapidly accelerating mass can be stopped before damage is done either to the equipment or to surroundings.

It should be added that where a steam-type feedworks is converted to a water-drive feedworks, see FIGS. 1 and 2, then the ports and 16 will be plugged and the conduits 19 and 20, together with their associated equipment, removed. The end fitting device 24 may be reinstalled to the right of tee 33, or may be replaced by an equivalent packing gland S with associated journaling structure, as desired. Furthermore, in the use of a rotatable type valve as shown in FIG. 3, cylinder 91 should be dimensioned such that a rotational displacement of the valve gate 46 is between fully open and metered or partially closed position. If the valve is to be rotated to a fully closed position, a suitable metering aperture should be provided in the valve to avoid any chances of impact shock damage. Any occurrence of power failure will, of course, be accompanied by a deenergization of solenoid 72 in FIG. 6, by way of example, so that valve 36 in FIG. 3 will remain closed until power is again available.

Relative to the safety feature, the same may be installed at either or both extremities of travel relative to carriage 28 or proximate thereto. Again, a suitable device such as this illustrated in FIGS. 6 and 7, so that carriage speed may be utilized to automatically activate the safety, valve-closure system.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

lclaim:

1. A sawmill feedworks, in combination, an operating cylinder having a piston, a piston rod coupled to said piston and extending outwardly out of and beyond said cylinder, a track means, a reciprocating carriage ridably engaging said track means and connected to said piston rod and being constructed and arranged to reciprocate back and forth in accordance with the reciprocation of said piston, means connected to said cylinder for introducing fluid into said cylinder such as to fluid-drive said piston back and forth within said cylinder and, hence, said carriage beyond said cylinder, and means, including electrical means, responsive to an excessive speed of travel, above a maximum allowable speed, of said carriage at a designated area of travel thereof for automatically conditioning said fluid-drive to decelerate the movement of said piston and, hence, of said carriage proximate said designated area, said electrical means being responsive to electrical power failure thereto for stopping piston and carriage travel.

2. The structure of claim 1 wherein said fluid introducing means comprises means for introducing hydraulic fluid into said cylinder, for the purpose set forth.

3. Structure according to claim 1 wherein said conditioning means comprises said electrical means responsive to said excessive speed of travel for generating an electrical pulse, and electromechanical means responsive to said electrical pulse for so conditioning said fluid-drive.

4. Structure according to claim 1 wherein said operating cylinder includes fluid conduit coupled to opposite extremities thereof, said fluid introducing means comprising means for circulating, back and forth, fluid within said conduit, valve means interposed in said conduit for restricting fluid-flow therein at desired times, said conditioning means comprising said electrical means responsive to said excessive speed of travel for generating an electrical impulse, an electromechanical means intercoupling said electrical means with said valve means for actuating said valve means to constrict fluid flow within said conduit in response to the presence of said electrical impulse.

5. Structure according to claim 1 wherein said conditioning means comprises means for stopping fluid-flow and thereby interrupting said fluid-drive, to stop the movement of said piston and, hence, of said carriage proximate said designated area.

6. Structure according to claim 1 wherein said fluid introducing means comprises conduit means connected to op posite ends of said cylinder for powering said piston in a double-action movement, said fluid introducing means for applying fluid to said conduit at desired times, valve means interposed in said conduit means for changing flow through said conduit from full-flow to metered condition, said conditioning means comprising means for sensing said excessive speed to produce an energy pulse, and means intercoupled between said sensing means and said valve for changing the condition of said valve to a metered condition upon the occurrence of said energy pulse.

7. A sawmill feedworks, in combination, an operating cylinder having a piston, a piston rod coupled to said piston and extending outwardly beyond said cylinder, track means, a reciprocating carriage ridably engaging said track means and connected to said piston rod, fluid conduit connected to said cylinder on opposite sides of said piston for all positions of travel of the latter, for supplying fluid to said conduit to fluiddrive said piston in a desired one of two reverse directions, a valve interposed in said fluid conduit for metering fluid-flow therein, and means, including electrical means, responsive to the speed of travel of said piston rod and also responsive to electrical power failure relative to said electrical means for metering said valve.

8. A sawmill feedworks, in combination, an operating cylinder having a piston, a piston rod coupled to said piston and extending outwardly beyond said cylinder, track means, a reciprocating carriage ridably engaging said track means and connected to said piston rod, fluid conduit connected to said cylinder on opposite sides of said piston for all positions of travel of the latter, for supplying fluid to said conduit to fluiddrive said piston in a desired one of two reverse directions, a valve interposed in said fluid conduit for closing fluid-flow therein, and means, including electrical means, responsive to the speed of travel of said piston rod and also responsive to electrical power failure relative to said electrical means for closing said valve.

HHIYH)

Claims (8)

1. A sawmill feedworks, in combination, an operating cylinder having a piston, a piston rod coupled to said piston and extending outwardly out of and beyond said cylinder, a track means, a reciprocating carriage ridably engaging said track means and connected to said piston rod and being constructed and arranged to reciprocate back and forth in accordance with the reciprocation of said piston, means connected to said cylinder for introducing fluid into said cylinder such as to fluid-drive said piston back and forth within said cylinder and, hence, said carriage beyond said cylinder, and means, including electrical means, responsive to an excessive speed of travel, above a maximum allowable speed, of said carriage at a designated area of travel thereof for automatically conditioning said fluid-drive to decelerate the movement of said piston and, hence, of said carriage proximate said designated area, said electrical means being responsive to electrical power failure thereto for stopping piston and carriage travel.

2. The structure of claim 1 wherein said fluid introducing means comprises means for introducing hydraulic fluid into said cylinder, for the purpose set forth.

3. Structure according to claim 1 wherein said conditioning means comprises said electrical means responsive to said excessive speed of travel for generating an electrical pulse, and electromechanical means responsive to said electrical pulse for so conditioning said fluid-drive.

4. Structure according to claim 1 wherein said operating cylinder includes fluid conduit coupled to opposite extremities thereof, said fluid introducing means comprising means for circulating, back and forth, fluid within said conduit, valve means interposed in said conduit for restricting fluiD-flow therein at desired times, said conditioning means comprising said electrical means responsive to said excessive speed of travel for generating an electrical impulse, an electromechanical means intercoupling said electrical means with said valve means for actuating said valve means to constrict fluid flow within said conduit in response to the presence of said electrical impulse.

5. Structure according to claim 1 wherein said conditioning means comprises means for stopping fluid-flow and thereby interrupting said fluid-drive, to stop the movement of said piston and, hence, of said carriage proximate said designated area.

6. Structure according to claim 1 wherein said fluid introducing means comprises conduit means connected to opposite ends of said cylinder for powering said piston in a double-action movement, said fluid introducing means for applying fluid to said conduit at desired times, valve means interposed in said conduit means for changing flow through said conduit from full-flow to metered condition, said conditioning means comprising means for sensing said excessive speed to produce an energy pulse, and means intercoupled between said sensing means and said valve for changing the condition of said valve to a metered condition upon the occurrence of said energy pulse.

7. A sawmill feedworks, in combination, an operating cylinder having a piston, a piston rod coupled to said piston and extending outwardly beyond said cylinder, track means, a reciprocating carriage ridably engaging said track means and connected to said piston rod, fluid conduit connected to said cylinder on opposite sides of said piston for all positions of travel of the latter, for supplying fluid to said conduit to fluid-drive said piston in a desired one of two reverse directions, a valve interposed in said fluid conduit for metering fluid-flow therein, and means, including electrical means, responsive to the speed of travel of said piston rod and also responsive to electrical power failure relative to said electrical means for metering said valve.

8. A sawmill feedworks, in combination, an operating cylinder having a piston, a piston rod coupled to said piston and extending outwardly beyond said cylinder, track means, a reciprocating carriage ridably engaging said track means and connected to said piston rod, fluid conduit connected to said cylinder on opposite sides of said piston for all positions of travel of the latter, for supplying fluid to said conduit to fluid-drive said piston in a desired one of two reverse directions, a valve interposed in said fluid conduit for closing fluid-flow therein, and means, including electrical means, responsive to the speed of travel of said piston rod and also responsive to electrical power failure relative to said electrical means for closing said valve.

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