US3896693A - Gang saw with improved damping means - Google Patents

Abstract

A crankshaft cradle is provided to damp out vibrations in a gang saw. The cradle is used to support the crankshaft and is pivotally attached to the gang saw frame. Forces that would normally be transferred from the crankshaft to the frame are damped out by means of the movable cradle, the movable cradle being pivotally attached to the frame by pendulum links.

Description

United States Patent Johansson July 29, 1975 GANG SAW WITH IMPROVED DAMPING 2,740,436 4/1956 Woodruff 83/748 MEANS 3,763,716 10/1973 Blomberg 74/604 3,791,227 2/1974 Cherry 74/52 [75] Inventor: Tage Hjalmar Johansson.

Sollentuna, Sweden [73] Assignee: Kockum Industri Aktiebolag,

Soderhamn, Sweden [22] Filed: Apr. 5, 1974 [21] Appl. No.: 458,358

[30] Foreign Application Priority Data Apr. 13, 1973 Germany 2318820 [52] U.S. Cl. 83/748; 74/52; 74/604 [51] Int. Cl. B27B 3/12 [58] Field of Search 83/748. 751, 779; 74/604, 74/603, 44, 42, 52

[56] References Cited UNITED STATES PATENTS 834,958 11/1906 Wilkin 83/748 Primary ExaminerDonald R. Schran Attorney, Agent, or Firm-Cushman, Darby & Cushman [57] ABSTRACT A crankshaft cradle is provided to damp out vibrations in a gang saw. The cradle is used to support the crankshaft and is pivotally attached to the gang saw frame. Forces that would normally be transferred from the crankshaft to the frame are damped out by means of the movable cradle, the movable cradle being pivotally attached to the frame by pendulum links.

4 Claims, 4 Drawing Figures PATENTEI] JUL 2 9 I975 W F MM Fig. 4

GANG SAW WITH IMPROVED DAMPING MEANS BACKGROUND OF THE INVENTION This invention relates to gang saws. and more particularly to a device to aid in damping vibrations in a gang saw frame.

Gang saws are often used for the conversion of saw logs into boards and planks. The gang saws commonly used today have a main frame resting on a foundation wherein the frame has vertical guides for a sash in which the sash holds parallel vertical saw blades so that the blades may be reciprocated vertically in the main frame. In such a gang saw a crankshaft is typically coupled with the sash by means of a connecting rod.

The improvements made in recent years to gang saws of this kind relate to individual components, such as the saw blades, the sash and the bearings. The basic design, on the other hand, has not been changed and the problems relating to the gang saw vibrations still exist with the present-day gang saws. Therefore, a careful anchor ing of the main frame to a foundation is required. The vibrations to a substantial extent are caused by the strong fluctuating forces which are produced as a consequence of the movements of the sash, the connecting rod and the counterweight of the crankshaft and which are transmitted to the frame through the crankshaft.

Swedish patent 198,133 discloses the use of a freely oscillating weight on the top of a frame structure in which the natural frequency of the pendulum is adjusted to act in opposition to the vibrations of the main frame. This device has been found to be inadequate when applied to a typical gang saw, because a gang saw is subjected to a wide variation of vibrations, and a more responsive damping method is required.

Another Swedish patent No. 198,921, attempts to deal with the crankshaft to frame vibration problem by utilizing unbalanced weights connected to the crankshaft and rotated in opposite directions at the speed of the crankshaft to reduce vertical vibrations in the main frame. Such unbalanced weights must be driven by a separate power source from the crankshaft power source and are hence impractical.

The instant invention provides a solution to the vibration problem by employing a novel crankshaft cradle structure.

The object of the invention is to provide a gang saw of the kind hereinafter described in which the vibrations to the main frame are substantially reduced.

To this end, in the gang saw according to the invention, the crankshaft is rotatably journaled in a cradle which is carried by the main frame and movable relative to the main frame substantially horizontally and transversely of the axis of rotation of the crankshaft under the influence of the forces which the crankshaft imposes on the cradle during the rotation of the crankshaft.

Since the crankshaft is thus free to move relative to the main frame horizontally and transversely of its axis, it will, during its rotation, reciprocate horizontally at the frequency of the vertical reciprocation of the sash. This horizontal reciprocation has a phase shift relative to the vertical sash reciprocation such that the crankshaft is in its mean or center position when the sash is in its extreme positions and the crankshaft is at its extreme horizontal positions when the sash is at its center or mean position. These movements of the crankshaft result in a very substantial reduction of the fluctuations of the forces imposed on the main frame by the crankshaft and, hence, a substantial reduction of the vibrations of the main frame.

The movability of the cradle may be realized in different ways. For example, the cradle may be slidably mounted on straight, horizontal guides extending transversely of the crankshaft and resiliently urged towards its center position by springs opposing the reciprocation. Instead of straight guides the gang saw may have guides which are curved in the vertical direction such that the cradle is gradually raised relative to the main frame as it is displaced from the mean position on so that the reciprocation is opposed by the weight of the cradle and the crankshaft.

In the preferred embodiment, however, the cradle is suspended in pendulum fashion from the main frame on both sides of the crankshaft by means of pendulum links. Preferably the pendulum links are parallel or approximately parallel.

Additional objects of the present invention reside in the specific construction of the exemplary apparatus hereinafter particularly described in the specification and shown in the several drawings.

BRIEF DESCRIPTION OF THE DRAWINGS A gang saw constructed in accordance with the invention will be described hereinafter with reference to the accompanying drawings.

FIG. 1 is a side elevational view of one embodiment of the gang saw according to the invention.

FIG. 2 shows the lower portion of the gang saw as taken along lines 22 of FIG. 1.

FIG. 3 is a schematic drawing which illustrates the crankshaft movement in relation to an xy coordinate system.

FIG. 4 graphically illustrates the position of the sash along an x coordinate with respect to the position of the crankshaft along a y coordinate as the crankshaft is rotated through a phase angle, (b.

Novel features of the improved device in accordance with the present invention will be more readily understood from a consideration of the following description taken together with the accompanying drawing, in which certain preferred adaptations are illustrated with the various parts thereof identified by suitable reference characters in each of the views, and in which:

DETAILED DESCRIPTION OF THE INVENTION The gang saw as illustrated in FIG. I has a main frame 11 secured to a foundation 12. An electric or hydraulic motor 13 rotates a crank mechanism, which includes a crankshaft 14 supported by the lower portion of the main frame and a connecting rod 15. The crankshaft 14 is rotated at a constant speed. The upper portion of the main frame 11 is provided with vertical sash guides 16 and 16a which may be adjustable. These guides 16 and 16a coact with slide blocks 17 on a rigid sash 18 in which a plurality of parallel saw blades 19 are secured in vertical planes. The sash 18 is pivotally connected to the connecting rod 15 and thus moves up and down the main fram 11 when the crankshaft 14 is rotated. The crankshaft is provided with a counterweight (not shown) which is disposed diametrically opposite to the crank pin and serves to balance the weight of the sash and the connecting rod. Logs to be sawed are moved horizontally through the main frame 11 and the sash 18 by means of upper and lower feed rolls 20 in a manner well known. The feed rolls are adjustable in a vertical plane to accomodate logs of varying diamcters.

So far as it has been described above, the illustrated gang saw is conventional. The novel feature of this invention resides in the fact that the bearings 21 of the crankshaft 14 are not stationary in the main frame 11 but are rather mounted on a cradle 22 which is suspended in pendulum fashion from the main frame I! on both sides of the crankshaft 14 through four parallel links 23 of equal lengths. The cradle 22 includes two transverse beams 24 rigidly connected to each other through two longitudinal beams 25.

The cradle 22 can thus oscillate substantially horizontally and perpendicularly of the axis of rotation of the crankshaft; and excessive deflection may be prevented by fixed abutmcnts (not shown). The oscillation is free in the sense that the movements of the cradle are not positively guided, and within the limits fixed by abutments, are opposed only by friction, inertia forces and gravity. Because the cradle 22 is suspended in pendulum fashion by means of pendulum links 23, the cradle 22 is slightly raised as it is moved in one horizontal direction or the other from its mean position. The mean position is defined by the pendulum links 23 being vertical and the cradle 22 and the crankshaft 14 being in their lowermost position. Thus it can be seen that gravity always tends to return the cradle 22 to its mean position. As shown in FIG. I, the cradle 22 also carries the motor 13 which is connected by means of a belt 13a to a pulley 14a which drives crankshaft 14. The motor 13 thus is oscillated with the cradle 22.

As the sash I8 is reciprocated vertically in the main frame 11 during the sawing operation, cradle 22 and crankshaft 14 are oscillated transversely about their mean position on the pendulum links 23. This transverse oscillation is caused primarily by the counterweight (which offsets the center of gravity of the crankshaft from the axis of rotation) and is of the same frequency as the vertical reciprocation of the sash 18 but has a phase shift relative to the latter such that the eradlc 22 and the crankshaft 14 are in their left-hand extreme position (see FIG. I and FIG. 3) when the downwardly moving sash is about halfway to its lower extreme position. When the sash I8 is in its upper or lower extreme position. the cradle 22 and the crankshaft l4 are in their mean position, and when the upwardly moving sash 18 is about halfway to its upper extreme position, the cradle and the crankshaft are in their right-hand extreme position.

The amplitude of the transverse oscillation of the eradle 22 naturally depends on the geometry, the masses of the cradle 22 and the crankshaft l4 and the other moving parts, but for practical purposes may be considered independent of the speed of rotation of the crankshaft. As a non-limitating example. the deflection has been found to be about five cm in either horizontal direction from the mean position in a gang saw constructed in accordance with the invention where the combined mass of the cradle 22, the crankshaft 14, the connecting rod and the sash 18 is about 3,500 kilograms. In this example, the speed of rotation of the crankshaft is approximately 380 rpm, the length of the pendulum links 23 is approximately 24 cm and the transverse distance between the links 23, is approximately 150 cm.

In this gang saw, the combined tensile force in the pendulum links 23, i.e., the force imposed on the main frame 11 by the cradle 22, fluctuates between 7,300 and 8,400 pounds (32,300 and 37,400 Newtons). The vertical component of this force is almost exclusively the weight of the recited components. The horizontal force component fluctuates between 0 and 1,500 pounds (0 and 7,350 Newtons) in either direction. If the crankshaft 14 has been stationary in the main frame ll is the case in conventional gang saws, it has been found that the horizontal force component would have fluctuated between 0 and 31,000 pounds (0 and 137,000 Newtons). It may be readily appreciated that the foregoing specific embodiment results in a substantial reduction of the horizontal force component.

From a consideration of FIG. 3 and FIG. 4, it can be seen that when the crankshaft 14 is at its maximum positive or negative x coordinate position, the sash is at its mean or zero origin position on the y coordinate. Conversely, when the sash is displaced to its maximum positive or negative y coordinate position, the crankshaft is displaced to its mean or zero origin x coordinate position. Noting FIG. 4 in particular, there is shown the re lationship between the phase angle and the displacements along the x and y coordinates.

In the illustrated embodiment, the transverse oscillation is opposed almost exclusively by gravity. However, it would be within the scope of the invention to provide springs or other means constantly urging the cradle 22 towards its mean position. Naturally, the pendulum links 23 need not be exactly parallel and vertical in the mean position as shown but can be disposed such that they are slightly inclined to the vertical plane in the mean position.

Moreover. although in the illustrated embodiment the motor 13 is carried by and oscillates with the cradle 22, the motor 13 may be stationary relative to the frame 11. In this case the relative movements of the cradle and the motor are accomodated by the power transmission between the motor and the crankshaft.

The foregoing specific embodiment has been described for the purpose of illustrating the principles of the present invention, and the same is subject to modification without departure therefrom. Therefore, the invention includes all modifications encompassed within the spirit and scope of the appended claims.

What is claimed is:

1. In a gang saw having a frame and a driven crankshaft, means for substantially damping out vibrations transferred from the crankshaft to the frame, said damping means comprising:

a. means for operatively journaling said crankshaft said means comprising a cradle,

b. means for movably securing said journaling means to said frame wherein said movably securing means allows substantially horizontal displacement of said crankshaft with respect to said frame when said crankshaft has a force applied thereto and,

wherein said movably securing means comprises a plurality of links, each of said links being pivotally connected to said cradle and pivotally connected to said frame,

wherein said links are disposed in substantially parallel relationship to each other which enable said cradle to be displaced in a substantially horizontal direction when a connecting rod imparts a rotational movement to said crankshaft,

said connecting rod is operatively connected at a distal end from said crankshaft to one end of a series of substantially parallel saw blades, said distal end being operatively connected to one end of said saw blades by means of a first sash vertically displaceable within a first vertical guide disposed in said frame, and

wherein said saw blades have their opposite end being operatively connected by means of a second sash vertically displaceable within a second vertical guide disposed in said frame.

so that when said first sash and said second sash are said horizontal mean and extreme positions of said crankshaft resulting from a pendulum-like movement of said cradle caused by forces applied to said saw blades and asid connecting rod from a wood sawing operation.

2. A gang saw comprising:

a. a frame,

b. a sash having a plurality of parallel vertical saw blades,

c drive means for reciprocating said sash up and down in said frame and including a crankshaft rotatable about an axis and a connecting rod interconnecting said sash and said crankshaft.

d. means journaling said crankshaft. and

e. means movably securing said journaling means to said frame and allowing oscillation of said journaling means and said crankshaft with respect to the frame independently of the reciprocation of the sash and in a substantially horizontal direction transverse to the axis of rotation of said crankshaft.

3. A gang saw as recited in claim 2 wherein said journaling means comprises a cradle and wherein said securing means comprises a plurality of links, each of said links being pivotally connected to said cradle and pivotally connected to said frame.

4. A gang saw as recited in claim 3 wherein said links are disposed in substantially parallel relationship to each other and pivotally connected to said cradle on either side of said crankshaft.

Claims (4)

1. In a gang saw having a frame and a driven crankshaft, means for substantially damping out vibrations transferred from the crankshaft to the frame, said damping means comprising: a. means for operatively journaling said crankshaft, b. means for movably securing said journaling means to said frame wherein said movably securing means allows substantially horizontal displacement of said crankshaft with respect to said frame when said crankshaft has a force applied thereto, said journaling means comprises a cradle and wherein said movably securing means comprises a plurality of links, each of said links being pivotally connected to said cradle and pivotally connected to said frame, said links are disposed in substantially parallel relationship to each other which enable said cradle to be displaced in a substantially horizontal direction when a connecting rod imparts a rotational movement to said crankshaft, said connecting rod is operatively connected at a distal end from said crankshaft to one end of a series of substantially parallel saw blades, said distal end being operatively connected to one end of said saw blades by means of a first sash vertically displaceable within a first vertical guide disposed in said frame, and wherein said saw blades have their opposite end being operatively connected by means of a second sash vertically displaceable within a second vertical guide disposed in said frame, so that when said first sash and said second sash are vertically displaced to a mean vertical position, said crankshaft will be correspondingly displaced to a substantially horizontal extreme position with respect to said frame, and when said first sash and said second sash are displaced to their extreme vertical positions, said crankshaft will be correspondingly positioned in a horizontal mean position with respect to said frame, said horizontal mean and extreme positions of said crankshaft resulting from a pendulum-like movement of said cradle caused by forces applied to said saw blades and asid connecting rod from a wood sawing operation.

2. A gang saw comprising: a. a frame, b. a sash having a plurality of parallel vertical saw blades, c. drive means for reciprocating said sash up and down in said frame and including a crankshaft rotatable about an axis and a connecting rod interconnecting said sash and said crankshaft, D. means journaling said crankshaft, and e. means movably securing said journaling means to said frame and allowing oscillation of said journaling means and said crankshaft with respect to the frame independently of the reciprocation of the sash and in a substantially horizontal direction transverse to the axis of rotation of said crankshaft.

3. A gang saw as recited in claim 2 wherein said journaling means comprises a cradle and wherein said securing means comprises a plurality of links, each of said links being pivotally connected to said cradle and pivotally connected to said frame.

4. A gang saw as recited in claim 3 wherein said links are disposed in substantially parallel relationship to each other and pivotally connected to said cradle on either side of said crankshaft.

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