CA1322933C - Bandmill with automatic track and strain control system - Google Patents
Bandmill with automatic track and strain control systemInfo
- Publication number
- CA1322933C CA1322933C CA000560632A CA560632A CA1322933C CA 1322933 C CA1322933 C CA 1322933C CA 000560632 A CA000560632 A CA 000560632A CA 560632 A CA560632 A CA 560632A CA 1322933 C CA1322933 C CA 1322933C
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- Prior art keywords
- wheel
- arbor
- blade
- support frame
- bandmill
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- Expired - Lifetime
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Abstract
Abstract A bandmill has first and second wheels and an endless saw blade trained about the wheels. The wheels are mounted to rotate about respective axes which lie in a common plane, but the first wheel is adjustable in position relative to the second wheel with respect to both its distance from the second wheel and its orientation relative to the second wheel. A tensioning mechanism is effective to force the first wheel away from the second wheel, while maintaining the axes of rotation of the two wheels substantially parallel, in response to a signal which is provided by a load cell and repre-sents the tension in the saw blade. A wheel tilt mechanism is effective to adjust the angular posi-tion of the first wheel relative to the second wheel in response to a signal indicating the path followed by the saw blade, for maintaining the blade on a proper path.
Description
1 ~22933 BANDMILL WITH AUTOMATIC TRACK
AND STRAIN CONTROL SYSTEM
Background of the Invention This invention relates to a bandmill having an automatic track and strain control system.
A bandmill is used for cutting lumber. A
conventional vertical bandmill comprises a support frame, two wheels, one disposed vertically above the other, and an endless saw blade trained about the wheels. The lower wheel is driven and the upper wheel idles. The blade is maintained under tension, and accordingly when the lower wheel is driven the blade passes endlessly about the wheels. A cutting throat is provided between the upper and lower wheels along the downward run of the blade. In order to ensure that the blade remains in position on the wheels, the wheels are crowned and their relative positions are accurately determined so that the plane containing the maximum circumference of the upper wheel coincides with the plane containing the maximum circumference of the lower wheel. This need for accurate positioning of wheels implies that the conventional bandmill is expensive to construct because a massive support structure is required in order to support the wheels with the required degree of stability.
The support structure that is conventionally used for a bandmill comprises a concrete base and a support frame mounted on the base. The support A
AND STRAIN CONTROL SYSTEM
Background of the Invention This invention relates to a bandmill having an automatic track and strain control system.
A bandmill is used for cutting lumber. A
conventional vertical bandmill comprises a support frame, two wheels, one disposed vertically above the other, and an endless saw blade trained about the wheels. The lower wheel is driven and the upper wheel idles. The blade is maintained under tension, and accordingly when the lower wheel is driven the blade passes endlessly about the wheels. A cutting throat is provided between the upper and lower wheels along the downward run of the blade. In order to ensure that the blade remains in position on the wheels, the wheels are crowned and their relative positions are accurately determined so that the plane containing the maximum circumference of the upper wheel coincides with the plane containing the maximum circumference of the lower wheel. This need for accurate positioning of wheels implies that the conventional bandmill is expensive to construct because a massive support structure is required in order to support the wheels with the required degree of stability.
The support structure that is conventionally used for a bandmill comprises a concrete base and a support frame mounted on the base. The support A
frame includes a mechanism for adjusting the vertical position of the upper wheel, whereby the tension in the blade can be adjusted. However, if the upper wheel is moved, it is then necessary to readjust the relative positions of the wheels to achieve precise coincidence of the planes containing the maximum circumference of the two wheels.
Sometimes, it is desirable to employ a bandmill in which the blade passes through the cutting throat in the horizontal direction, or at an angle that is inclined to the horizontal. However, the support structure of the vertical bandmill does not permit ready adjustment of the orientation of the bandmill.
The nature of the support structure also implies that the orientation in which a given bandmill will be used is fixed at the time of manufacture, and accordingly it is necessary to build distinct bandmills for vertical, horizontal and inclined use.
The support structure for the conventional bandmill is not only massive but is also bulky.
If two conventional bandmills are disposed in the same orientation and on the same side of the cutting path, they cannot be any closer together than about two feet. It is proposed in co-pending Canadian Patent Application Serial No. 577,351 filed September 14, 1988, that a sa-~mill should be provided in which any three bandmills out of a group of four bandmills act on a single log on a single pass of the log through a bandmill station. The four bandmills are stationary with respect to the direction of feed of the log through the group of bandmills. The sawmill is designed to process logs that are only eight feet long. The cutting edges . ,~", ` 3 1 322933 of the saw blades must therefore be closer together than about two feet, since otherwise the sawing by the upstream bandmill will be completed before the log starts to be sawn by the downstream bandmill, and this may create difficulties in log handling.
During sawing, the saw blade of a conventional bandmill vibrates in the cutting throat. If the blade is dull or the feed rate is high, the blade tends to snake out of the desired cutting plane as a log is fed through the throat. Consequently, lumber with rough surfaces or of uneven thickness is produced. Moreover, snaking may result in the blade being deflected to such an extent that it strikes other parts of the bandmill, resulting in damage to the bandmill. Hitherto, these problems have been addressed by using a thicker blade, which results in greater kerf loss, or increasing the blade tension, which results in higher maintenance costs.
When the blade of a bandmill is deflected, e.g., d~e to nonuniformities in the log being cut, there is a tendency for blade oscillations to occur, resulting in thicker kerf and impaired ac-curacy.
The stress distribution in the blade of a bandmill depends on the path followed by the blade relative to the wheels, and the stress distribution has a bearing on sawing accuracy. It has been found that improved accuracy is obtained if the bottoms of the gullets of the teeth are maintained close to the edges of the wheels, so that the stiff-ness of the blade in the teeth area is maximized.
However, if the gullets pass over the wheels, there is a tendency for the saw blade to crack in the vicinity of the gullets.
Summary of the Invention In accordance with a first aspect of the present invention there is provided a bandmill comprising a support frame, a first wheel, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, two carriages in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, a second wheel mounted in the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, a differential lever assembly having first and second levers which are mounted pivotally to the support frame and engage the two carriages respectively, tensioning means for forcing the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range, and wherein the tensioning means and the tilt means 3~ comprise a first force member that is effective between the support frame and the first lever and a second force member that is effective between the second lever and the first lever.
In accordance with a second aspect of the present inventiGn there is provided a bandmill 1 3~33 comprising a support frame, a bandmill comprising a support frame, a first wheel, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, first and second arbor supports in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, first and second link members effective on the first and second arbor supports respectively, a second wheel mounted in the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, tensioning means for acting on the arbor supports to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for acting on the arbor supports to adjust the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined rane, and wherein the tensioning means comprise first force means effective between the support frame and the first link member and the tilt means comprise second force means effective between the first link member and the second link member.
In accordance with a third aspect of the present invention there is provided a bandmill comprising a support frame, first, second and third wheels, means supporting the second and third `~' '''~
5a 1 322933 wheels relative to the support frame for rotating about the respective axes, an arbor having two opposite ends and on which the first wheel is mounted, an endless saw blade trained about the wheels, a lever assembly having two levers by which the two opposite ends of the arbor are supported respectively, wherein the two levers are mounted to pivot about a common axis which is parallel to the axes of rotation of the second and third wheels and is stationary with respect thereto, tensioning means effective to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting upon the tensioning means to maintain the tension at a predetermined value, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of at least one other wheel, and tilt control means for sensing the path along which the blade passes and acting upon the tilt means for maintaining the blade on a predetermined path, and wherein the tensioning means and the tilt means comprise a first force member which is effective between the support frame and one of the two levers and a second force member which is effective between said one lever and the other lever.
By providing for adjustment of the tilt of the first wheel, it is possible to avoid the need for the massive support structures that are used in conventional bandmills, since the tile mechanism maintains the saw blade on the proper path. The tensioning mechanism enables a high blade tension to be achieved, so that the amplitude of blade vibration is reduced, and this results in ~,~..
5b 1 3~2~33 consistent sawing. However, the tension is controlled so that it remains low enough that unacceptable maintenance costs are avoided.
In accordance with a fourth aspect of the present invention there is provided a bandmill comprising a support frame composed of two column members and means connecting the column members and maintaining them in spaced, substantially parallel relationship, a first wheel disposed between the two column members, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, two carriages in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, a second wheel disposed between the two column members and mounted to the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, tensioning means for forcing the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range.
Use of such a support structure ensures that when the support structure is moved, the wheel arbors remain in the same relative positions unless one or both of the wheel arbors is moved relative .~,.~ .
5c 1 322q33 to the support structure, and this in turn permits the orientation of the bandmill apparatus to be ; changed, e.g., from a vertical orientation, without its being necessary to dismantle and rebuild the entire bandmill apparatus. This in turn implies that a given bandmill can be installed in any orientation.
In accordance with a fifth aspect of the present invention there is provided a bandmill comprising a support frame composed of first and second frame members, first and second arbor supports mounted on the first and second frame members respectively and movable relative to the support frame, a first arbor having two opposite ends received by the first and second arbor supports respectively, a first wheel mounted on the first arbor for rotation about an axis of the first wheel and disposed between the first and second frame members, a second arbor supported by the first and second frame members at locations spaced apart along the second arbor, a second wheel mounted on the second arbor for rotation about an axis of the second wheel and disposed between the first and second frame members, an endless saw blade trained about the wheels, tensioning means for acting on the arbor supports to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for acting on the arbor supports to adjust the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control ~' p,~
1 322~33 5d means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range.
In accordance with a sixth aspect of the present invention there is provided a bandmill comprising a support frame, an endless saw blade, first and second substantially co-planar wheels spaced apart along a longitudinal axis of the support frame and carrying the endless saw blade, the first wheel being tiltable about a second axis that is substantially normal to the longitudinal axis to vary tracking of the saw blade on the wheels, saw tracking sensing means for producing a tracking output signal which reflects tracking of the saw blade relative to the wheels, and saw tracking control means responsive to the tracking output signal for selectively tilting said first wheel to maintain the saw blade within a desired tracking range, said saw tracking sensing means comprising first and second non-contact sensors, mounting means for mounting the sensors relative to the saw blade so that when the saw blade is within a desired tracking range the first sensor detects gullets of the saw blade and the second sensor detect continuous metal of the saw blade remote from the gullets, the first and second sensors providing first and second sensor output signals respectively, and comparator means for processing the sensor output signals and generating a comparator output signal responsive to the first and second sensor output signals.
In accordance with a seventh aspect of the present invention there is provided a bandmill comprising a support frame having a longitudinal ~, 5e 1 ~22q 33 axis and composed of first and second generally flat side members spaced apart and disposed generally parallel to each other, the first side member comprising a first guide means extending substantially parallel to the longitudinal axis and the second side member comprising a second guide means extending substantially parallel to the longitudinal axis, said first and second guide means being at one end of the support frame, and the bandmill further comprising an endless toothed saw blade, first and second substantially co-planar wheels spaced apart along said longitudinal axis and carrying the endless saw blade, the wheels being located between the first and second side members, a first wheel arbor journalling the first wheel for rotation, first and second carriages mounted on the first and second guide means respectively for movement therealong and carrying the first wheel arbor, a second wheel arbor journalling the second wheel for rotation at the end of the support frame opposite said one end, and arbor moving means located between the first and second side members and engaging the first and second carriages for selectively moving the first and second carriages along the longitudinal axis.
In accordance with an eighth aspect of the present invention there is provided a bandmill comprising a support frame having a longitudinal axis and composed of first and second side members spaced apart and disposed generally parallel to each other, an endless toothed saw blade, first and second substantially co-planar wheels spaced apart along the longitudinal axis of the support frame and carrying the endless saw blade, the wh~els being located between the first and second side ~' ;''; ~'' 5f 1 322933 members, a first wheel arbor journalling the first wheel for rotation, first and second arbor mounting means for carrying the first wheel arbor and cooperating with the first and second side members respectively at one end of the support frame to permit guided movement of the arbor mounting means relative to the support frame, which movement is generally parallel to the longitudinal axis, a second wheel arbor journalling the second wheel for rotation at the end of the support frame opposite said one end, and arbor moving means located between the first and second side members and engaging the first and second arbor mounting means for selectively moving the first and second arbor mounting means along said longitudinal axis, said arbor moving means comprising a first force transmission member engaging the first arbor mounting means, a second force transmission member engaging the second arbor mounting means, first power means effective between the support frame and the first force transmission member, and second power means effective between the first force transmission member and the second force transmission member.
In accordance with a ninth aspect of the present invention there is provided a bandmill comprising a body, an endless toothed saw, first and second substantially co-planar wheels spaced apart along a longitudinal axis of the body and carrying the endless saw, a first wheel arbor journalling the first wheel for rotation, the first wheel arbor having first and second end portions, first and second arbor mounting means for carrying the first and second end portions of the first wheel arbor, the arbor mounting means being guided ~,.-.
,.. .
5g 1 322933 for movement relative to the body in directions parallel to said longitudinal axis, a first force transmission member movable relative to the body and engaging the first arbor mounting means, a second force transmission member movable relative to the body and engaging the second arbor mounting means, a tilt adjustment power means effective between the first and second force transmission members for moving the first and second arbor mounting means differentially, parallel to the longitudinal axis of the body, to vary tilt of said first wheel so as to vary track of the saw on the wheels, and a strain adjustment power means effective between the body and said first force transmission member for moving the first and second arbor mounting means together, parallel to the longitudinal axis of the body, to vary saw strain.
Brief Description of the Drawinqs For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:
FIG. 1 is a side elevation of a horizontal two-wheel bandmill embodying the present invention, FIG. 2 is a sectional view to an enlarged scale showing the manner of mounting of the driven wheel of the FIG. 1 bandmill, FIG. 3 is a vertical sectional view to an enlarged scale showing the manner of mounting of the idler wheel of the FIG. 1 bandmill, FIG. 4 is a side elevation, partly cut away, showing the idler wheel of the FIG. 1 bandmill and the tilt and strain mechanisms therefor, FIG. 5 is a partial vertical sectional view of the FIG. 1 bandmill illustrating the idler wheel and the tilt and strain mechanism, FIG. 6 illustrates part of the blade of the FIG. 1 bandmill and shows features relevant to the positioning of sensor units, FIG. 7 illustrates the arrangement of sensor units relative to the blade, FIG. 8 illustrates the control circuit for the tilt and strain mechanisms, FIG. 9 illustrates waveforms used in explaining the operation of the tilt mechanisms, FIG. 10 illustrates a modification of FIG. 3, FIG. 11 is a simplified side view of a three-wheel bandmill embodying the present invention, and FIG. 12 is a sectional view of the FIG. 11 bandmill, taken on the line XII-XII of FIG. 11.
The FIG. 1 bandmill is illustrated in the drawings in a vertical orientation. However, it is disposed horizontally when in use.
In the different figures of the drawings, like reference numerals denote corresponding elements.
In FIGS. 11 and 12, primed reference numerals de-note elements having similar functions to the ele-ments denoted by the corresponding unprimed numer-als in FIG. 9.
7 ~ 3~z3 Detailed Description The bandmill illustrated in FIGS. 1-8 comprises a support frame 4, a driven wheel 6, an idler wheel 8, and an endless saw blade 66, which is shown in 5 FIGS. 6 and 7 but not in FIGS. 1-5. The support frame 4 comprises two rigid steel columns 4A and 4B
which are held in spaced apart, parallel relation-ship, e.g. by plates 4C that are welded to the columns 4A, 4B. As shown in FIG. 2, the driven wheel 6 is ~eyed to an arbor 10 which is journalled in bearings 14. The bearings 14 are mounted in the columns 4A, 4B respectively. The wheel 6 is coupled by way of the arbor 10 to a hydraulic drive motor 17, which receives hydraulic fluid under pressure from a pump 32 (FIG. 8) by way of a valve 34, which is controlled by a solenoid 134. The valve 34 has a first position in which it delivers fluid under pressure from the p~mp 32 to the motor 17, for driving the motor, and a second position in which it ~0 prevents delivery of fluid to the motor. The coupling between the motor 17 and the arbor 10 is through sheaves and belts, but it may alternatively be a direct drive coupling. The idler wheel 8 (FIG.
3) is journalled on an arbor 12 by means of bearings 16. The arbor 12 is supported at its two opposite ends in spherical bearings 50 which are themselves supported in respective carriages 52. The carriages 52 are slidable along rods 54 which are secured rigidly to the support frame 4, bearings 53 being disposed between the carriages 52 and the rods 54.
A differential lever acsembly comprising two cranked levers 22A and 22B (FI~S. 1, 4, 5) is mounted on a shaft 24 of the support frame 4 by way of sleeve bearings. The lever assembly is accom-modated between the two columns 4A, 4B. Each lever 22 has two arms 40 and 42. At their ends fartherfrom the shaft 24, the arms 40 carry rollers which engage wear plates on the carriages 50 respective-ly. At its end farther from the shaft 24, the arm 42A is coupled to the support frame by way of a single-acting hydraulic cylinder 28 and is coupled to the arm 42B by way of a double-acting hydraulic cylinder 30. As shown in FIG. 8, the cylinders 28 and 30 are connected to the pump 32 by way of respective valves 36 and 38. The valve 36 is a servo valve that is controlled by a solenoid 136 and delivers fluid under pressure to the cylinder 28 to extend the cylinder, or allows hydraulic fluid to leave the cylinder, so that the cylinder can retract, at a rate dependent on the magnitude of the current received by the solenoid 136. The valve 38 is controlled by two solenoids 138b and 138f and has a first position in which it delivers fluid under pressure to one chamber of the cylinder 30 and allows fluid to leave the other chamber of the cylinder 30, a second position in which it allows fluid to leave the one chamber and delivers fluid under pressure to the other chamber, and a third position in which fluid does not enter or leave either chamber except through leakage.
Upon delivery of fluid under pressure to the cylinder 28, the lever assembly is urged to pivot about the axis of the shaft 24 in the clockwise direction shown in FIG. 1, with the relative angu-lar positions of the arms 42 depending on thecondition of the valve 38. The carriages 50 are forced away from the wheel 6 (to the left of FIG.
1) and the wheel 8 also is forced away from the wheel 6. In this manner, the saw blade is placed under tension. The differential nature of the 1 322q33 lever assembly allows the arbor 12,and the wheel 8 carried thereby, to be tilted to a selected extent relative to the arbor 10 and the wheel 6.
A load cell 70 is interposed between the cylin-S der 28 and the arm 42A and provides a pressuresignal representative of the force exerted by the cylinder 28 on the lever 22A. The tension in the saw blade 12 depends upon the force exerted by the cylinder 28, and the pressure signal provided by the load cell 70 is applied to a programmable logic controller (PLC) 72 (FIG. 8). The PLC 72 compares the tension value indicated by the pressure signal with a pre-set range of values. If the tension value indicated by the pressure signal is outside the pre-set range, the PLC provides a current to the solenoid 136 of appropriate magnitude and direction, using an analog PID control loop, to restore the indicated tension value to the pre-set range of values. In this manner, the tension in the saw blade is maintained substantially constant. In the event that the preseure signal starts to vary in oscillating fashion, implying that the blade is oscillating, the controller 72 adjusts the valve 36 so as to damp the oscillation without reducing the blade tension substantially.
FIG. 6 illustrates a portion of the saw blade 66 in plan, at a location in the cutting throat.
It will be seen from FIG. 6 that each tooth 61 is generally triangular in form and that adjacent teeth are separated by gullets 63.
The plane of the forward edge of the driven wheel 6 (the upstream edge with respect to the direction of lumber flow) intersects the plane defining the nominal position of the blade 66 in the cutting throat in a line 68. For proper opera-lo 1 322~33 tion of the bandmill, the line 62 that defines the base of the gullets must lie just forward of the line 68. It is desirable that the line 62 be 1/16"
+/- 1/16" forward of the line 68.
Three sensor units 64b, 64f and 64c are mounted above the plane of the lower run of the blade 66, just upstream (with respect to the direction of movement of the blade) of the cutting throat 60.
The sensor units 64 are used to sense the presence of the blade or its teeth at predetermined loca-tions. It is known to use inductive sensors to sense the presence of a metal object, such as a saw blade, but the short range of conventional inductive sensors renders them less than optimal for detecting whether the blade of a bandmill is at a desired position. Thus, the blade is likely to depart from its nominal path by a distance greater than the range of an inductive sensor, resulting in a possi-bility that the blade will strike the sensor and destroy it, Therefore, use of ~hotoelectric sensor units is preferred. In the preferred embodiment of the invention, each sensor unit is of the kind manufactured b~ Banner Engineering Corp. and sold under the designation SBCI-6. The sensor unit includes a light source (a light-emitting diode) and a photodetector (a photodiode). As shown in FIG. 7, each sensor unit 64 emits a light beam along an optical axis 104. The light beam is directed towards the saw blade. Light incident on the saw blade creates a reflected beam which is collected by the sensor unit 64 and is directed onto the photode-tector. The LED is imaged onto the photodetector if the saw blade is at a distance of from 5 to 7 inches from the sensor unit. The sensor unit provides a 24 volt d.c. output signal if the LED remains imaged on 1 322~33 the photodetector for a time longer than the response time of the sensor unit, and otherwise its output is at 0 volts. The output signals provided by the sensor units are applied to the PLC 72. In order to immunize the sensor unit from the influences of ambient light, the light beam provided by the sensor unit is modu-lated in intensity at 10 kHz and the signal provided by the photodetector is demodulated against a reference signal at 10 kHz. Demodulation occurs over 10 cycles of the reference signal, and accordingly the response time of the sensor unit is 1 ms.
The optical axis 104b of the sensor unit 64b is vertical and intersects the plane of the blade at a distance Dl from the line 68. The optical axis 104f of the sensor unit 64f is vertical and intersects the plane of the blade at a distance D2 from the line 68. When the blade is in the ideal position relative to the wheel 6, the line 64 that defines the position on the teeth where the length of the gullet is equal to half the distance between the points of the teeth is at a distance D from the line 68, and the distance Dl is equal to D plus 1/16" whereas the distance D2 is equal to D minus 1/16". Therefore, when the blade is within the proper tracking range, the light intensity received by each of the sensor unit 64b and 64f varies substantially in accordance with a rectangular waveform, with the duty cycle of the intensity waveform for the sensor 64b somewhat less than 50%
and the duty cycle of the intensity waveform for the sensor 64f somewhat more than 50%.
In an embodiment of the invention, the saw blade is driven at a speed of 10,000 ft/min (50.80 m/s) and the teeth are at a pitch of 1.75 in (4.445 cm). Accordingly, the frequency at which the light 12 t 322933 intensity received by the sensor units 64b, 64f varies at normal operating speed is about 1143 Hz, corresponding to a period of 0.875 ms. However, when the bandmill is started, the frequency at which the light intensity received by the sensor units 64b, 64f varies is much less than 1143 Hz, and the frequency increases as the blade is accele-rated. FIG. 9 illustrates four pairs of waveforms A, B, C, and D, in which the upper waveform of each pair represents the variation in light intensity received by the unit 64b at a given blade speed and the lower waveform represents the corresponding variation in the output voltage provided by the unit 64b.
The PLC 72 includes digital filters 72b, 72f which receive the output signals provided by the sensor units 64b, 64f and provide bi-level output signals for analysis by the PLC. The output signal provided by the filter 72b or 72f is high if the duty cycle of the intensity waveform received by the appropriate sensor unit is greater than 50% and low if the duty cycle is less than 50%. During start-up of the bandmill, the digital filters are adjusted to take account of the progressive increase in the frequency of the intensity waveforms. Ad-justment of the filters is performed automatically as a function of time, because variations in the rate at which the speed of the blade increases during start-up are quite small.
~hen the 2ath of the blade shifts forwards from the ideal position by more than 1/16", the duty cycle of the intensity waveform for the sensor unit 64b becomes greater than 50~ and therefore the output voltase provided by the filter 72b will go high~ Conversely, when the path shifts backwards from the ideal position by more than 1/16", the duty cycle of the intensity waveform for the unit 64f becomes less than 50% and the output signal provided by the filter 72f will go low. The signals provided by the filters 72b and 72f therefore indi-cate whether the path along which the saw blade is passing is within the proper range. If the blade is displaced vertically by more than about 1 inch from its ideal position, the intens.ty of reflected light received by the sensor units 64 is not suf-ficient to cause the detector to respond and ac-cordingly the output voltages provided by the sen-sor units go low.
During operation of the bandmill, the PLC
functions both in a control mode and in a diag-nostic mode. In the control mode, action is taken by the PLC on the basis of the output provided by a single sensor unit 64f or 69b. In particular, if the output voltage of the filter 72b goes high, indicating that the blade is forward of the proper tracking range, the PLC provides an output signal to energize the solenoid 138b momentarily. Energi-zation of the solenoid 138b causes the valve 38 to deliver fluid to the double-acting cylinder 30 in the sense to force the backward end of the arbor 12 away from the arbor 10 relative to the forward end of the arbor 12. This change in the orientation of the idler wheel tends to shift the blade backwards.
Conversely, if the output voltage provided by the filter 72f goes low, the solenoid 138f is energized and the resulting change in orientation of the idler wheel tends tc shift the blade forwards. The delay ti~e through the sensors, the PLC and valve drive solenoids 138f, 138b, between the blade shifting out of the proper tracking range and the 1~ ~ 322933 valve 38 being adjusted in response thereto, is about 50 ms. In order to prevent overcompensation, the controller 72 samples the outputs of the fil-ters 72b, 72f at intervals longer than 50 ms, so that the effect of each adjustment of the valve 38 on the output signals of the filters 72b, 72f can be observed before another adjust~ent is made.
The third sensor unit 64c is positioned to illuminate, and receive light reflected from, a region of the blade that is in the center of the blade with respect to the direction of lumher flow.
Normally, the output signal provided by the unit 64c is high. In the diagnostic mode, the PLC
diagnoses hardware faults in the tracking control system. In ~articular, if the output signals of the filters 72b and 72f are high and the output signal of the sensor unit 64c is low, an indication is given that the sensor unit 64c is faulty; and if the output signals of the filter 72b and the sensor unit 64c are high but that of the filter 72f is low, an indication is given that the sensor unit 64b is faulty. Also, if the tracking of the blade is being adjusted, by energizing one of the sole-noids 138b, 138f, and adjustment continues over more than 20 seconds without the blade being de-tected as having been restored to the proper track-ing range, an indication of a fault in the double-acting solenoid valve is given.
The PLC is also able to diagnose faulty con-ditions in the sawing operation: if the outputsignals of the filter 72f and the sensor unit 64c both go low while the output signal of the load cell remains at an acceptable level, an indication that the blade is snaking is given, and the log ~ 322933 feed is slowed down or stopped. If slowing or stopping the log feed does not result in the output signal of the filter 72f and the sensor unit 64c going high, the motor 17 is sto2ped. If the output signal of the sensor unit 64c goes low and the output signal of the load cell indicates that the tension in the blade is too low, an indication that the blade is broken is given, and the motor 17 is stopped.
Switches 139f and 139b are connected to the solenoids 138f and 138b to allow manual adjustment of the valve 38. Similarly, a switch 135 is pro-vided to allow the motor to be stopped under operator control.
FIG. 10 shows a modification of FIG. 3, ac-cording to which the upper wheel 8 is keyed to the arbor 12. The opposite ends of the arbor are journalled in bearings 78 which are supported by the carriages 52. The bearings 78 permit both tilting and rotation of the arbor 12.
The bandmill shown in FIGS. 11 and 12 is a three-wheel bandmill having a driven wheel 6 and two idler wheels 8 and 80. The idler wheel 8 is keyed to the arbor 12, and the arbor 12 is mounted in the support frame 4 by means of bearings (not shown) which are stationary relative to the bear-ings of the arbor 10. The third wheel is supported by bearings on an arbor 82 which is mounted in the support frame g by way of a lever assembly com-prising levers 22A' and 22B'. The levers 22' pivot about the central axis of a shaft 24', and each lever has two arms 40' and 42'. At their ends farther from the shaft 24', the arms 40' carry respective spherical ~earings 84. The two spheri-c21 bearings 84 receive the opposite ends of the arbor 82. At its end farther fro~ the shaft 24', the arm 42A' is coupled to the support frame by way of a hydraulic cylinder 28 and is coupled to the arm 42B' by way of a hydraulic cylinder 30.
S The bandmills illustrated in FIGS. 1-10 are preferred over that of FIGS. 11 and 12 because the wheel 80 of the FIGS. 1] and 12 bandmill is much smaller in diameter than the wheels 6 and 8 and therefore the blade undergoes more severe bending stresses when passing around the wheel 80 than when passing around the wheels 6 and 8.
It will be appreciated that the present inven-tion is not restricted to the particular embodi-ments that have been described and illustrated, and that variations may be made therein without de-parting from the scope of the invention as defined in the appended claims and equivalents thereof.
For example, it is not essential to the invention in its broadest aspects that the tilting of the wheel 8 or 80 ta~e place by applying forces in the same direction as the forces used to tension the saw blade. Other methods of sensing the path fol-lowed by the saw blade than use of photodetectors in the manner described above may be used. The invention is not restricted to the load cell being in the position shown in the drawings. Two load cells may be provided between the arbor 12 and the lever assemblies 40a and 40b respectively.
Sometimes, it is desirable to employ a bandmill in which the blade passes through the cutting throat in the horizontal direction, or at an angle that is inclined to the horizontal. However, the support structure of the vertical bandmill does not permit ready adjustment of the orientation of the bandmill.
The nature of the support structure also implies that the orientation in which a given bandmill will be used is fixed at the time of manufacture, and accordingly it is necessary to build distinct bandmills for vertical, horizontal and inclined use.
The support structure for the conventional bandmill is not only massive but is also bulky.
If two conventional bandmills are disposed in the same orientation and on the same side of the cutting path, they cannot be any closer together than about two feet. It is proposed in co-pending Canadian Patent Application Serial No. 577,351 filed September 14, 1988, that a sa-~mill should be provided in which any three bandmills out of a group of four bandmills act on a single log on a single pass of the log through a bandmill station. The four bandmills are stationary with respect to the direction of feed of the log through the group of bandmills. The sawmill is designed to process logs that are only eight feet long. The cutting edges . ,~", ` 3 1 322933 of the saw blades must therefore be closer together than about two feet, since otherwise the sawing by the upstream bandmill will be completed before the log starts to be sawn by the downstream bandmill, and this may create difficulties in log handling.
During sawing, the saw blade of a conventional bandmill vibrates in the cutting throat. If the blade is dull or the feed rate is high, the blade tends to snake out of the desired cutting plane as a log is fed through the throat. Consequently, lumber with rough surfaces or of uneven thickness is produced. Moreover, snaking may result in the blade being deflected to such an extent that it strikes other parts of the bandmill, resulting in damage to the bandmill. Hitherto, these problems have been addressed by using a thicker blade, which results in greater kerf loss, or increasing the blade tension, which results in higher maintenance costs.
When the blade of a bandmill is deflected, e.g., d~e to nonuniformities in the log being cut, there is a tendency for blade oscillations to occur, resulting in thicker kerf and impaired ac-curacy.
The stress distribution in the blade of a bandmill depends on the path followed by the blade relative to the wheels, and the stress distribution has a bearing on sawing accuracy. It has been found that improved accuracy is obtained if the bottoms of the gullets of the teeth are maintained close to the edges of the wheels, so that the stiff-ness of the blade in the teeth area is maximized.
However, if the gullets pass over the wheels, there is a tendency for the saw blade to crack in the vicinity of the gullets.
Summary of the Invention In accordance with a first aspect of the present invention there is provided a bandmill comprising a support frame, a first wheel, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, two carriages in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, a second wheel mounted in the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, a differential lever assembly having first and second levers which are mounted pivotally to the support frame and engage the two carriages respectively, tensioning means for forcing the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range, and wherein the tensioning means and the tilt means 3~ comprise a first force member that is effective between the support frame and the first lever and a second force member that is effective between the second lever and the first lever.
In accordance with a second aspect of the present inventiGn there is provided a bandmill 1 3~33 comprising a support frame, a bandmill comprising a support frame, a first wheel, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, first and second arbor supports in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, first and second link members effective on the first and second arbor supports respectively, a second wheel mounted in the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, tensioning means for acting on the arbor supports to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for acting on the arbor supports to adjust the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined rane, and wherein the tensioning means comprise first force means effective between the support frame and the first link member and the tilt means comprise second force means effective between the first link member and the second link member.
In accordance with a third aspect of the present invention there is provided a bandmill comprising a support frame, first, second and third wheels, means supporting the second and third `~' '''~
5a 1 322933 wheels relative to the support frame for rotating about the respective axes, an arbor having two opposite ends and on which the first wheel is mounted, an endless saw blade trained about the wheels, a lever assembly having two levers by which the two opposite ends of the arbor are supported respectively, wherein the two levers are mounted to pivot about a common axis which is parallel to the axes of rotation of the second and third wheels and is stationary with respect thereto, tensioning means effective to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting upon the tensioning means to maintain the tension at a predetermined value, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of at least one other wheel, and tilt control means for sensing the path along which the blade passes and acting upon the tilt means for maintaining the blade on a predetermined path, and wherein the tensioning means and the tilt means comprise a first force member which is effective between the support frame and one of the two levers and a second force member which is effective between said one lever and the other lever.
By providing for adjustment of the tilt of the first wheel, it is possible to avoid the need for the massive support structures that are used in conventional bandmills, since the tile mechanism maintains the saw blade on the proper path. The tensioning mechanism enables a high blade tension to be achieved, so that the amplitude of blade vibration is reduced, and this results in ~,~..
5b 1 3~2~33 consistent sawing. However, the tension is controlled so that it remains low enough that unacceptable maintenance costs are avoided.
In accordance with a fourth aspect of the present invention there is provided a bandmill comprising a support frame composed of two column members and means connecting the column members and maintaining them in spaced, substantially parallel relationship, a first wheel disposed between the two column members, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, two carriages in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, a second wheel disposed between the two column members and mounted to the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, tensioning means for forcing the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range.
Use of such a support structure ensures that when the support structure is moved, the wheel arbors remain in the same relative positions unless one or both of the wheel arbors is moved relative .~,.~ .
5c 1 322q33 to the support structure, and this in turn permits the orientation of the bandmill apparatus to be ; changed, e.g., from a vertical orientation, without its being necessary to dismantle and rebuild the entire bandmill apparatus. This in turn implies that a given bandmill can be installed in any orientation.
In accordance with a fifth aspect of the present invention there is provided a bandmill comprising a support frame composed of first and second frame members, first and second arbor supports mounted on the first and second frame members respectively and movable relative to the support frame, a first arbor having two opposite ends received by the first and second arbor supports respectively, a first wheel mounted on the first arbor for rotation about an axis of the first wheel and disposed between the first and second frame members, a second arbor supported by the first and second frame members at locations spaced apart along the second arbor, a second wheel mounted on the second arbor for rotation about an axis of the second wheel and disposed between the first and second frame members, an endless saw blade trained about the wheels, tensioning means for acting on the arbor supports to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for acting on the arbor supports to adjust the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control ~' p,~
1 322~33 5d means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range.
In accordance with a sixth aspect of the present invention there is provided a bandmill comprising a support frame, an endless saw blade, first and second substantially co-planar wheels spaced apart along a longitudinal axis of the support frame and carrying the endless saw blade, the first wheel being tiltable about a second axis that is substantially normal to the longitudinal axis to vary tracking of the saw blade on the wheels, saw tracking sensing means for producing a tracking output signal which reflects tracking of the saw blade relative to the wheels, and saw tracking control means responsive to the tracking output signal for selectively tilting said first wheel to maintain the saw blade within a desired tracking range, said saw tracking sensing means comprising first and second non-contact sensors, mounting means for mounting the sensors relative to the saw blade so that when the saw blade is within a desired tracking range the first sensor detects gullets of the saw blade and the second sensor detect continuous metal of the saw blade remote from the gullets, the first and second sensors providing first and second sensor output signals respectively, and comparator means for processing the sensor output signals and generating a comparator output signal responsive to the first and second sensor output signals.
In accordance with a seventh aspect of the present invention there is provided a bandmill comprising a support frame having a longitudinal ~, 5e 1 ~22q 33 axis and composed of first and second generally flat side members spaced apart and disposed generally parallel to each other, the first side member comprising a first guide means extending substantially parallel to the longitudinal axis and the second side member comprising a second guide means extending substantially parallel to the longitudinal axis, said first and second guide means being at one end of the support frame, and the bandmill further comprising an endless toothed saw blade, first and second substantially co-planar wheels spaced apart along said longitudinal axis and carrying the endless saw blade, the wheels being located between the first and second side members, a first wheel arbor journalling the first wheel for rotation, first and second carriages mounted on the first and second guide means respectively for movement therealong and carrying the first wheel arbor, a second wheel arbor journalling the second wheel for rotation at the end of the support frame opposite said one end, and arbor moving means located between the first and second side members and engaging the first and second carriages for selectively moving the first and second carriages along the longitudinal axis.
In accordance with an eighth aspect of the present invention there is provided a bandmill comprising a support frame having a longitudinal axis and composed of first and second side members spaced apart and disposed generally parallel to each other, an endless toothed saw blade, first and second substantially co-planar wheels spaced apart along the longitudinal axis of the support frame and carrying the endless saw blade, the wh~els being located between the first and second side ~' ;''; ~'' 5f 1 322933 members, a first wheel arbor journalling the first wheel for rotation, first and second arbor mounting means for carrying the first wheel arbor and cooperating with the first and second side members respectively at one end of the support frame to permit guided movement of the arbor mounting means relative to the support frame, which movement is generally parallel to the longitudinal axis, a second wheel arbor journalling the second wheel for rotation at the end of the support frame opposite said one end, and arbor moving means located between the first and second side members and engaging the first and second arbor mounting means for selectively moving the first and second arbor mounting means along said longitudinal axis, said arbor moving means comprising a first force transmission member engaging the first arbor mounting means, a second force transmission member engaging the second arbor mounting means, first power means effective between the support frame and the first force transmission member, and second power means effective between the first force transmission member and the second force transmission member.
In accordance with a ninth aspect of the present invention there is provided a bandmill comprising a body, an endless toothed saw, first and second substantially co-planar wheels spaced apart along a longitudinal axis of the body and carrying the endless saw, a first wheel arbor journalling the first wheel for rotation, the first wheel arbor having first and second end portions, first and second arbor mounting means for carrying the first and second end portions of the first wheel arbor, the arbor mounting means being guided ~,.-.
,.. .
5g 1 322933 for movement relative to the body in directions parallel to said longitudinal axis, a first force transmission member movable relative to the body and engaging the first arbor mounting means, a second force transmission member movable relative to the body and engaging the second arbor mounting means, a tilt adjustment power means effective between the first and second force transmission members for moving the first and second arbor mounting means differentially, parallel to the longitudinal axis of the body, to vary tilt of said first wheel so as to vary track of the saw on the wheels, and a strain adjustment power means effective between the body and said first force transmission member for moving the first and second arbor mounting means together, parallel to the longitudinal axis of the body, to vary saw strain.
Brief Description of the Drawinqs For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:
FIG. 1 is a side elevation of a horizontal two-wheel bandmill embodying the present invention, FIG. 2 is a sectional view to an enlarged scale showing the manner of mounting of the driven wheel of the FIG. 1 bandmill, FIG. 3 is a vertical sectional view to an enlarged scale showing the manner of mounting of the idler wheel of the FIG. 1 bandmill, FIG. 4 is a side elevation, partly cut away, showing the idler wheel of the FIG. 1 bandmill and the tilt and strain mechanisms therefor, FIG. 5 is a partial vertical sectional view of the FIG. 1 bandmill illustrating the idler wheel and the tilt and strain mechanism, FIG. 6 illustrates part of the blade of the FIG. 1 bandmill and shows features relevant to the positioning of sensor units, FIG. 7 illustrates the arrangement of sensor units relative to the blade, FIG. 8 illustrates the control circuit for the tilt and strain mechanisms, FIG. 9 illustrates waveforms used in explaining the operation of the tilt mechanisms, FIG. 10 illustrates a modification of FIG. 3, FIG. 11 is a simplified side view of a three-wheel bandmill embodying the present invention, and FIG. 12 is a sectional view of the FIG. 11 bandmill, taken on the line XII-XII of FIG. 11.
The FIG. 1 bandmill is illustrated in the drawings in a vertical orientation. However, it is disposed horizontally when in use.
In the different figures of the drawings, like reference numerals denote corresponding elements.
In FIGS. 11 and 12, primed reference numerals de-note elements having similar functions to the ele-ments denoted by the corresponding unprimed numer-als in FIG. 9.
7 ~ 3~z3 Detailed Description The bandmill illustrated in FIGS. 1-8 comprises a support frame 4, a driven wheel 6, an idler wheel 8, and an endless saw blade 66, which is shown in 5 FIGS. 6 and 7 but not in FIGS. 1-5. The support frame 4 comprises two rigid steel columns 4A and 4B
which are held in spaced apart, parallel relation-ship, e.g. by plates 4C that are welded to the columns 4A, 4B. As shown in FIG. 2, the driven wheel 6 is ~eyed to an arbor 10 which is journalled in bearings 14. The bearings 14 are mounted in the columns 4A, 4B respectively. The wheel 6 is coupled by way of the arbor 10 to a hydraulic drive motor 17, which receives hydraulic fluid under pressure from a pump 32 (FIG. 8) by way of a valve 34, which is controlled by a solenoid 134. The valve 34 has a first position in which it delivers fluid under pressure from the p~mp 32 to the motor 17, for driving the motor, and a second position in which it ~0 prevents delivery of fluid to the motor. The coupling between the motor 17 and the arbor 10 is through sheaves and belts, but it may alternatively be a direct drive coupling. The idler wheel 8 (FIG.
3) is journalled on an arbor 12 by means of bearings 16. The arbor 12 is supported at its two opposite ends in spherical bearings 50 which are themselves supported in respective carriages 52. The carriages 52 are slidable along rods 54 which are secured rigidly to the support frame 4, bearings 53 being disposed between the carriages 52 and the rods 54.
A differential lever acsembly comprising two cranked levers 22A and 22B (FI~S. 1, 4, 5) is mounted on a shaft 24 of the support frame 4 by way of sleeve bearings. The lever assembly is accom-modated between the two columns 4A, 4B. Each lever 22 has two arms 40 and 42. At their ends fartherfrom the shaft 24, the arms 40 carry rollers which engage wear plates on the carriages 50 respective-ly. At its end farther from the shaft 24, the arm 42A is coupled to the support frame by way of a single-acting hydraulic cylinder 28 and is coupled to the arm 42B by way of a double-acting hydraulic cylinder 30. As shown in FIG. 8, the cylinders 28 and 30 are connected to the pump 32 by way of respective valves 36 and 38. The valve 36 is a servo valve that is controlled by a solenoid 136 and delivers fluid under pressure to the cylinder 28 to extend the cylinder, or allows hydraulic fluid to leave the cylinder, so that the cylinder can retract, at a rate dependent on the magnitude of the current received by the solenoid 136. The valve 38 is controlled by two solenoids 138b and 138f and has a first position in which it delivers fluid under pressure to one chamber of the cylinder 30 and allows fluid to leave the other chamber of the cylinder 30, a second position in which it allows fluid to leave the one chamber and delivers fluid under pressure to the other chamber, and a third position in which fluid does not enter or leave either chamber except through leakage.
Upon delivery of fluid under pressure to the cylinder 28, the lever assembly is urged to pivot about the axis of the shaft 24 in the clockwise direction shown in FIG. 1, with the relative angu-lar positions of the arms 42 depending on thecondition of the valve 38. The carriages 50 are forced away from the wheel 6 (to the left of FIG.
1) and the wheel 8 also is forced away from the wheel 6. In this manner, the saw blade is placed under tension. The differential nature of the 1 322q33 lever assembly allows the arbor 12,and the wheel 8 carried thereby, to be tilted to a selected extent relative to the arbor 10 and the wheel 6.
A load cell 70 is interposed between the cylin-S der 28 and the arm 42A and provides a pressuresignal representative of the force exerted by the cylinder 28 on the lever 22A. The tension in the saw blade 12 depends upon the force exerted by the cylinder 28, and the pressure signal provided by the load cell 70 is applied to a programmable logic controller (PLC) 72 (FIG. 8). The PLC 72 compares the tension value indicated by the pressure signal with a pre-set range of values. If the tension value indicated by the pressure signal is outside the pre-set range, the PLC provides a current to the solenoid 136 of appropriate magnitude and direction, using an analog PID control loop, to restore the indicated tension value to the pre-set range of values. In this manner, the tension in the saw blade is maintained substantially constant. In the event that the preseure signal starts to vary in oscillating fashion, implying that the blade is oscillating, the controller 72 adjusts the valve 36 so as to damp the oscillation without reducing the blade tension substantially.
FIG. 6 illustrates a portion of the saw blade 66 in plan, at a location in the cutting throat.
It will be seen from FIG. 6 that each tooth 61 is generally triangular in form and that adjacent teeth are separated by gullets 63.
The plane of the forward edge of the driven wheel 6 (the upstream edge with respect to the direction of lumber flow) intersects the plane defining the nominal position of the blade 66 in the cutting throat in a line 68. For proper opera-lo 1 322~33 tion of the bandmill, the line 62 that defines the base of the gullets must lie just forward of the line 68. It is desirable that the line 62 be 1/16"
+/- 1/16" forward of the line 68.
Three sensor units 64b, 64f and 64c are mounted above the plane of the lower run of the blade 66, just upstream (with respect to the direction of movement of the blade) of the cutting throat 60.
The sensor units 64 are used to sense the presence of the blade or its teeth at predetermined loca-tions. It is known to use inductive sensors to sense the presence of a metal object, such as a saw blade, but the short range of conventional inductive sensors renders them less than optimal for detecting whether the blade of a bandmill is at a desired position. Thus, the blade is likely to depart from its nominal path by a distance greater than the range of an inductive sensor, resulting in a possi-bility that the blade will strike the sensor and destroy it, Therefore, use of ~hotoelectric sensor units is preferred. In the preferred embodiment of the invention, each sensor unit is of the kind manufactured b~ Banner Engineering Corp. and sold under the designation SBCI-6. The sensor unit includes a light source (a light-emitting diode) and a photodetector (a photodiode). As shown in FIG. 7, each sensor unit 64 emits a light beam along an optical axis 104. The light beam is directed towards the saw blade. Light incident on the saw blade creates a reflected beam which is collected by the sensor unit 64 and is directed onto the photode-tector. The LED is imaged onto the photodetector if the saw blade is at a distance of from 5 to 7 inches from the sensor unit. The sensor unit provides a 24 volt d.c. output signal if the LED remains imaged on 1 322~33 the photodetector for a time longer than the response time of the sensor unit, and otherwise its output is at 0 volts. The output signals provided by the sensor units are applied to the PLC 72. In order to immunize the sensor unit from the influences of ambient light, the light beam provided by the sensor unit is modu-lated in intensity at 10 kHz and the signal provided by the photodetector is demodulated against a reference signal at 10 kHz. Demodulation occurs over 10 cycles of the reference signal, and accordingly the response time of the sensor unit is 1 ms.
The optical axis 104b of the sensor unit 64b is vertical and intersects the plane of the blade at a distance Dl from the line 68. The optical axis 104f of the sensor unit 64f is vertical and intersects the plane of the blade at a distance D2 from the line 68. When the blade is in the ideal position relative to the wheel 6, the line 64 that defines the position on the teeth where the length of the gullet is equal to half the distance between the points of the teeth is at a distance D from the line 68, and the distance Dl is equal to D plus 1/16" whereas the distance D2 is equal to D minus 1/16". Therefore, when the blade is within the proper tracking range, the light intensity received by each of the sensor unit 64b and 64f varies substantially in accordance with a rectangular waveform, with the duty cycle of the intensity waveform for the sensor 64b somewhat less than 50%
and the duty cycle of the intensity waveform for the sensor 64f somewhat more than 50%.
In an embodiment of the invention, the saw blade is driven at a speed of 10,000 ft/min (50.80 m/s) and the teeth are at a pitch of 1.75 in (4.445 cm). Accordingly, the frequency at which the light 12 t 322933 intensity received by the sensor units 64b, 64f varies at normal operating speed is about 1143 Hz, corresponding to a period of 0.875 ms. However, when the bandmill is started, the frequency at which the light intensity received by the sensor units 64b, 64f varies is much less than 1143 Hz, and the frequency increases as the blade is accele-rated. FIG. 9 illustrates four pairs of waveforms A, B, C, and D, in which the upper waveform of each pair represents the variation in light intensity received by the unit 64b at a given blade speed and the lower waveform represents the corresponding variation in the output voltage provided by the unit 64b.
The PLC 72 includes digital filters 72b, 72f which receive the output signals provided by the sensor units 64b, 64f and provide bi-level output signals for analysis by the PLC. The output signal provided by the filter 72b or 72f is high if the duty cycle of the intensity waveform received by the appropriate sensor unit is greater than 50% and low if the duty cycle is less than 50%. During start-up of the bandmill, the digital filters are adjusted to take account of the progressive increase in the frequency of the intensity waveforms. Ad-justment of the filters is performed automatically as a function of time, because variations in the rate at which the speed of the blade increases during start-up are quite small.
~hen the 2ath of the blade shifts forwards from the ideal position by more than 1/16", the duty cycle of the intensity waveform for the sensor unit 64b becomes greater than 50~ and therefore the output voltase provided by the filter 72b will go high~ Conversely, when the path shifts backwards from the ideal position by more than 1/16", the duty cycle of the intensity waveform for the unit 64f becomes less than 50% and the output signal provided by the filter 72f will go low. The signals provided by the filters 72b and 72f therefore indi-cate whether the path along which the saw blade is passing is within the proper range. If the blade is displaced vertically by more than about 1 inch from its ideal position, the intens.ty of reflected light received by the sensor units 64 is not suf-ficient to cause the detector to respond and ac-cordingly the output voltages provided by the sen-sor units go low.
During operation of the bandmill, the PLC
functions both in a control mode and in a diag-nostic mode. In the control mode, action is taken by the PLC on the basis of the output provided by a single sensor unit 64f or 69b. In particular, if the output voltage of the filter 72b goes high, indicating that the blade is forward of the proper tracking range, the PLC provides an output signal to energize the solenoid 138b momentarily. Energi-zation of the solenoid 138b causes the valve 38 to deliver fluid to the double-acting cylinder 30 in the sense to force the backward end of the arbor 12 away from the arbor 10 relative to the forward end of the arbor 12. This change in the orientation of the idler wheel tends to shift the blade backwards.
Conversely, if the output voltage provided by the filter 72f goes low, the solenoid 138f is energized and the resulting change in orientation of the idler wheel tends tc shift the blade forwards. The delay ti~e through the sensors, the PLC and valve drive solenoids 138f, 138b, between the blade shifting out of the proper tracking range and the 1~ ~ 322933 valve 38 being adjusted in response thereto, is about 50 ms. In order to prevent overcompensation, the controller 72 samples the outputs of the fil-ters 72b, 72f at intervals longer than 50 ms, so that the effect of each adjustment of the valve 38 on the output signals of the filters 72b, 72f can be observed before another adjust~ent is made.
The third sensor unit 64c is positioned to illuminate, and receive light reflected from, a region of the blade that is in the center of the blade with respect to the direction of lumher flow.
Normally, the output signal provided by the unit 64c is high. In the diagnostic mode, the PLC
diagnoses hardware faults in the tracking control system. In ~articular, if the output signals of the filters 72b and 72f are high and the output signal of the sensor unit 64c is low, an indication is given that the sensor unit 64c is faulty; and if the output signals of the filter 72b and the sensor unit 64c are high but that of the filter 72f is low, an indication is given that the sensor unit 64b is faulty. Also, if the tracking of the blade is being adjusted, by energizing one of the sole-noids 138b, 138f, and adjustment continues over more than 20 seconds without the blade being de-tected as having been restored to the proper track-ing range, an indication of a fault in the double-acting solenoid valve is given.
The PLC is also able to diagnose faulty con-ditions in the sawing operation: if the outputsignals of the filter 72f and the sensor unit 64c both go low while the output signal of the load cell remains at an acceptable level, an indication that the blade is snaking is given, and the log ~ 322933 feed is slowed down or stopped. If slowing or stopping the log feed does not result in the output signal of the filter 72f and the sensor unit 64c going high, the motor 17 is sto2ped. If the output signal of the sensor unit 64c goes low and the output signal of the load cell indicates that the tension in the blade is too low, an indication that the blade is broken is given, and the motor 17 is stopped.
Switches 139f and 139b are connected to the solenoids 138f and 138b to allow manual adjustment of the valve 38. Similarly, a switch 135 is pro-vided to allow the motor to be stopped under operator control.
FIG. 10 shows a modification of FIG. 3, ac-cording to which the upper wheel 8 is keyed to the arbor 12. The opposite ends of the arbor are journalled in bearings 78 which are supported by the carriages 52. The bearings 78 permit both tilting and rotation of the arbor 12.
The bandmill shown in FIGS. 11 and 12 is a three-wheel bandmill having a driven wheel 6 and two idler wheels 8 and 80. The idler wheel 8 is keyed to the arbor 12, and the arbor 12 is mounted in the support frame 4 by means of bearings (not shown) which are stationary relative to the bear-ings of the arbor 10. The third wheel is supported by bearings on an arbor 82 which is mounted in the support frame g by way of a lever assembly com-prising levers 22A' and 22B'. The levers 22' pivot about the central axis of a shaft 24', and each lever has two arms 40' and 42'. At their ends farther from the shaft 24', the arms 40' carry respective spherical ~earings 84. The two spheri-c21 bearings 84 receive the opposite ends of the arbor 82. At its end farther fro~ the shaft 24', the arm 42A' is coupled to the support frame by way of a hydraulic cylinder 28 and is coupled to the arm 42B' by way of a hydraulic cylinder 30.
S The bandmills illustrated in FIGS. 1-10 are preferred over that of FIGS. 11 and 12 because the wheel 80 of the FIGS. 1] and 12 bandmill is much smaller in diameter than the wheels 6 and 8 and therefore the blade undergoes more severe bending stresses when passing around the wheel 80 than when passing around the wheels 6 and 8.
It will be appreciated that the present inven-tion is not restricted to the particular embodi-ments that have been described and illustrated, and that variations may be made therein without de-parting from the scope of the invention as defined in the appended claims and equivalents thereof.
For example, it is not essential to the invention in its broadest aspects that the tilting of the wheel 8 or 80 ta~e place by applying forces in the same direction as the forces used to tension the saw blade. Other methods of sensing the path fol-lowed by the saw blade than use of photodetectors in the manner described above may be used. The invention is not restricted to the load cell being in the position shown in the drawings. Two load cells may be provided between the arbor 12 and the lever assemblies 40a and 40b respectively.
Claims (31)
1. A bandmill comprising a support frame, a first wheel, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, two carriages in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, a second wheel mounted in the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, a differential lever assembly having first and second levers which are mounted pivotally to the support frame and engage the two carriages respectively, tensioning means for forcing the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range, and wherein the tensioning means and the tilt means comprise a first force member that is effective between the support frame and the first lever and a second force member that is effective between the second lever and the first lever.
2. A bandmill according to claim 1, wherein the tension control means comprise a force sensor that is effective to measure the force applied to the first lever by the first force member, and a controller that receives the measured value of the force applied to the first lever by the first force member and controls the first force member to maintain the measured value within a predetermined range.
3. A bandmill according to claim 1, wherein the tilt control means comprise sensor means for sensing the path along which the blade passes, and a controller that controls the second force member to maintain the sensed path within the range of predetermined paths.
4. A bandmill according to claim 3, wherein the sensor means comprise first and second photodetectors for collecting light reflected from the saw blade and generating electrical signals representative of the power at which light is received by the photodetectors respectively, the first photodetector being positioned to collect light reflected from the teeth of the blade when the blade is passing along a path within the predetermined range of paths and the second photodetector being positioned to collect light reflected from the body of the blade when the blade is passing along a path within the predetermined range of paths.
5. A bandmill according to claim 1, wherein the first and second force members are hydraulic cylinders.
6. A bandmill according to claim 1, wherein the first and second levers comprise first and second bell-crank members respectively, each bell-crank member being journaled for pivotal movement relative to the support frame and having first and second arms extending from the axis of pivotal movement, the first arms of the first and second bell-crank members being in engagement with the two carriages respectively, the first force member being effective between the support frame and the second arm of the first bell-crank member and the second force member being effective between the second arm of the first bell-crank member and the second arm of the second bell-crank member.
7. A bandmill comprising a support frame composed of two column members and means connecting the column members and maintaining them in spaced, substantially parallel relationship, a first wheel disposed between the two column members, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, two carriages in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, a second wheel disposed between the two column members and mounted to the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, tensioning means for forcing the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range.
8. A bandmill according to claim 7, wherein the two carriages are mounted to the two column members respectively and are movable independently of each other relative to the support frame, whereby the angular position of the first wheel relative to the support frame is adjustable, and the bandmill further comprises a second arbor having two opposite ends and on which the second wheel is mounted, the two opposite ends of the second arbor being mounted to the two column members respectively in a manner preventing movement of the second arbor relative to the support frame in directions perpendicular to said axis of rotation of the second wheel.
9. A bandmill according to claim 8, comprising a differential lever assembly having first and second levers which are mounted pivotally to the support frame and are disposed in the space between the two column members, the first and second levers engaging the two carriages respec-tively, and wherein the tensioning means and the tilt means comprise a first force member that is effective between the support frame and the first lever and a second force member that is effective between the second lever and the first lever.
10. A bandmill according to claim 9, wherein the tension control means comprise a force sensor that is effective to measure the force applied to the first lever by the first force member, and a controller that receives the measured value of the force applied to the first lever by the first force member and controls the first force member to maintain the measured value within a predetermined range.
11. A bandmill according to claim 10, wherein the force sensor comprises a load cell disposed between the first force member and the first lever.
12. A bandmill according to claim 9, wherein the tilt control means comprise sensor means for sensing the path along which the blade passes and a controller that controls the second force member to maintain the sensed path within the predetermined range of paths.
13. A bandmill according to claim 12, wherein the sensor means comprise first and second sensor units, which are stationary with respect to the support frame, for collecting light reflected from the saw blade and generating electrical signals representative of the duty cycle at which reflected light is collected by the sensor units respectively as the saw blade is driven along its path of movement, whereby the sensor units scan the saw blade, the sensor units being positioned to scan the saw blade along paths that cross the teeth of the blade at different levels of the teeth between the gullets and the tips of the teeth, whereby the duty cycle at which reflected light is collected by each sensor unit depends on the path of the blade.
14. A bandmill according to claim 13, wherein the positions of the first and second sensor units are selected such that when the blade is within the predetermined range of paths, the duty cycle at which reflected light is collected by the first sensor unit is less than 50% and the duty cycle at which reflected light is collected by the second sensor unit is greater than 50%, and the controller responds to the first sensor unit collecting reflected light at a duty cycle of more than 50% or the second sensor unit collecting reflected light at a duty cycle of less than 50% by controlling the second force member to restore the blade to the predetermined range of paths.
15. A bandmill according to claim 14, further comprising a third sensor unit, which is stationary with respect to the support frame, for collecting light reflected from the saw blade and generating an electrical signal representative of the power at which reflected light is collected by the third sensor unit as the blade is driven along its path of movement, whereby the third sensor unit scans the saw blade, the third sensor unit being positioned to scan the saw blade along a path that is substantially equidistant from the back of the blade and the gullets of the teeth of the blade, and wherein the controller is programmed to provide a fault indication if the controller receives a signal from the third sensor unit indicating that it is collecting reflected light at a predetermined power and receives a signal from the first sensor unit indicating that it is collecting light at a duty cycle of more than 50% but the controller does not receive a signal from the second sensor unit indicating that it is collecting light at a duty cycle of more than 50%.
16. A bandmill according to claim 13, further comprising a third sensor unit, which is stationary with respect to the support frame, for collecting light reflected from the saw blade and generating an electrical signal representative of the power at which reflected light is collected by the third sensor unit as the blade is driven along its path of movement, whereby the third sensor unit scans the saw blade, the third sensor unit being positioned to scan the saw blade along a path that is substantially equidistant from the back of the blade and the gullets of the teeth of the blade.
17. A bandmill according to claim 16, wherein the third sensor unit is connected to the controller and the controller is programmed to provide a fault indication if the output signals provided by the first and second sensor units indicate that they are collecting light reflected from the teeth of the blade but the controller does not receive a signal indicating that the third sensor unit is collecting reflected light at a predetermined power level.
18. A bandmill according to claim 16, wherein the tensioning control means comprise a force sensor which is effective to measure the force applied to the first lever by the first force member, and the controller receives the measured value of the force applied to the first lever by the first force member and controls the first force member to maintain the measured value substantially equal to a higher predetermined value, and the controller is programmed to provide a fault indication if the measured value of the force applied to the first lever by the first force member falls to a lower predetermined value and the controller does not receive a signal from the third sensor unit indicating that it is collecting reflected light at a predetermined power.
19. A bandmill according to claim 9, wherein each lever has first and second arms and the first arms of the two levers engage the two carriages respectively, and the first force member is effective between the support frame and the second arm of the first lever and the second force member is effective between the second arm of the second lever and the second arm of the first lever.
20. A bandmill according to claim 1, wherein each lever has a first arm and a second arm, the first arms of the two levers engaging the two carriages respectively, and the first force member is effective between the support frame and the second arm of the first lever and the second force member is effective between the second arm of the second lever and the second arm of the first lever.
21. A bandmill comprising a support frame, a first wheel, an arbor having two opposite ends and on which the first wheel is mounted for rotation about an axis thereof, first and second arbor supports in which the two opposite ends of the arbor are received respectively and which are movable relative to the support frame, first and second link members effective on the first and second arbor supports respectively, a second wheel mounted in the support frame for rotation about an axis of the second wheel, an endless saw blade trained about the wheels, tensioning means for acting on the arbor supports to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for acting on the arbor supports to adjust the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range, and wherein the tensioning means comprise first force means effective between the support frame and the first link member and the tilt means comprise second force means effective between the first link member and the second link member.
22. A bandmill according to claim 21, wherein the tension control means comprise a transducer that provides a signal dependent on the force applied to the first link member by the first force means, and a controller responsive to the transducer for controlling the first force means.
23. A bandmill comprising a support frame composed of first and second frame members, first and second arbor supports mounted on the first and second frame members respectively and movable relative to the support frame, a first arbor having two opposite ends received by the first and second arbor supports respectively, a first wheel mounted on the first arbor for rotation about an axis of the first wheel and disposed between the first and second frame members, a second arbor supported by the first and second frame members at locations spaced apart along the second arbor, a second wheel mounted on the second arbor for rotation about an axis of the second wheel and disposed between the first and second frame members, an endless saw blade trained about the wheels, tensioning means for acting on the arbor supports to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting automatically upon the tensioning means to maintain the tension in the blade within a predetermined range, tilt means for acting on the arbor supports to adjust the angular position of the axis of rotation of the first wheel relative to the axis of rotation of the second wheel, and tilt control means for sensing the path along which the blade passes and acting automatically upon the tilt means for maintaining the path of the blade within a predetermined range.
24. A bandmill according to claim 23, wherein the second wheel is keyed to the second arbor, and the second arbor is journaled in first and second bearings received by the first and second frame members respectively.
25. A bandmill comprising a support frame, first, second and third wheels, means supporting the second and third wheels relative to the support frame for rotating about the respective axes, an arbor having two opposite ends and on which the first wheel is mounted, an endless saw blade trained about the wheels, a lever assembly having two levers by which the two opposite ends of the arbor are supported respectively, wherein the two levers are mounted to pivot about a common axis which is parallel to the axes of rotation of the second and third wheels and is stationary with respect thereto, tensioning means effective to force the first wheel away from the second wheel so as to place the saw blade under tension, tension control means for measuring the tension in the blade and acting upon the tensioning means to maintain the tension at a predetermined value, tilt means for adjusting the angular position of the axis of rotation of the first wheel relative to the axis of rotation of at least one other wheel, and tilt control means for sensing the path along which the blade passes and acting upon the tilt means for maintaining the blade on a predetermined path, and wherein the tensioning means and the tilt means comprise a first force member which is effective between the support frame and one of the two levers and a second force member which is effective between said one lever and the other lever.
26. A bandmill according to claim 25, wherein the second and third wheels are of substantially the same diameter and the first wheel is of lesser diameter than the second and third wheels.
27. A bandmill comprising a support frame, an endless saw blade, first and second substantially co-planar wheels spaced apart along a longitudinal axis of the support frame and carrying the endless saw blade, the first wheel being tiltable about a second axis that is substantially normal to the longitudinal axis to vary tracking of the saw blade on the wheels, saw tracking sensing means for producing a tracking output signal which reflects tracking of the saw blade relative to the wheels, and saw tracking control means responsive to the tracking output signal for selectively tilting said first wheel to maintain the saw blade within a desired tracking range, said saw tracking sensing means comprising first and second non-contact sensors, mounting means for mounting the sensors relative to the saw blade so that when the saw blade is within a desired tracking range the first sensor detects gullets of the saw blade and the second sensor detect continuous metal of the saw blade remote from the gullets, the first and second sensors providing first and second sensor output signals respectively, and comparator means for processing the sensor output signals and generating a comparator output signal responsive to the first and second sensor output signals.
28. A bandmill comprising a support frame having a longitudinal axis and composed of first and second generally flat side members spaced apart and disposed generally parallel to each other, the first side member comprising a first guide means
29 extending substantially parallel to the longitudinal axis and the second side member comprising a second guide means extending substantially parallel to the longitudinal axis, said first and second guide means being at one end of the support frame, and the bandmill further comprising an endless toothed saw blade, first and second substantially co-planar wheels spaced apart along said longitudinal axis and carrying the endless saw blade, the wheels being located between the first and second side members, a first wheel arbor journalling the first wheel for rotation, first and second carriages mounted on the first and second guide means respectively for movement therealong and carrying the first wheel arbor, a second wheel arbor journalling the second wheel for rotation at the end of the support frame opposite said one end, and arbor moving means located between the first and second side members and engaging the first and second carriages for selectively moving the first and second carriages along the longitudinal axis.
29. A bandmill comprising a support frame having a longitudinal axis and composed of first and second side members spaced apart and disposed generally parallel to each other, an endless toothed saw blade, first and second substantially co-planar wheels spaced apart along the longitudinal axis of the support frame and carrying the endless saw blade, the wheels being located between the first and second side members, a first wheel arbor journalling the first wheel for rotation, first and second arbor mounting means for carrying the first wheel arbor and cooperating with the first and second side members respectively at one end of the support frame to permit guided movement of the arbor mounting means relative to the support frame, which movement is generally parallel to the longitudinal axis, a second wheel arbor journalling the second wheel for rotation at the end of the support frame opposite said one end, and arbor moving means located between the first and second side members and engaging the first and second arbor mounting means for selectively moving the first and second arbor mounting means along said longitudinal axis, said arbor moving means comprising a first force transmission member engaging the first arbor mounting means, a second force transmission member engaging the second arbor mounting means, first power means effective between the support frame and the first force transmission member, and second power means effective between the first force transmission member and the second force transmission member.
29. A bandmill comprising a support frame having a longitudinal axis and composed of first and second side members spaced apart and disposed generally parallel to each other, an endless toothed saw blade, first and second substantially co-planar wheels spaced apart along the longitudinal axis of the support frame and carrying the endless saw blade, the wheels being located between the first and second side members, a first wheel arbor journalling the first wheel for rotation, first and second arbor mounting means for carrying the first wheel arbor and cooperating with the first and second side members respectively at one end of the support frame to permit guided movement of the arbor mounting means relative to the support frame, which movement is generally parallel to the longitudinal axis, a second wheel arbor journalling the second wheel for rotation at the end of the support frame opposite said one end, and arbor moving means located between the first and second side members and engaging the first and second arbor mounting means for selectively moving the first and second arbor mounting means along said longitudinal axis, said arbor moving means comprising a first force transmission member engaging the first arbor mounting means, a second force transmission member engaging the second arbor mounting means, first power means effective between the support frame and the first force transmission member, and second power means effective between the first force transmission member and the second force transmission member.
30. A bandmill comprising a body, an endless toothed saw, first and second substantially co-planar wheels spaced apart along a longitudinal axis of the body and carrying the endless saw, a first wheel arbor journalling the first wheel for rotation, the first wheel arbor having first and second end portions, first and second arbor mounting means for carrying the first and second end portions of the first wheel arbor, the arbor mounting means being guided for movement relative to the body in directions parallel to said longitudinal axis, a first force transmission member movable relative to the body and engaging the first arbor mounting means, a second force
31 transmission member movable relative to the body and engaging the second arbor mounting means, a tilt adjustment power means effective between the first and second force transmission members for moving the first and second arbor mounting means differentially, parallel to the longitudinal axis of the body, to vary tilt of said first wheel so as to vary track of the saw on the wheels, and a strain adjustment power means effective between the body and said first force transmission member for moving the first and second arbor mounting means together, parallel to the longitudinal axis of the body, to vary saw strain.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US2209687A | 1987-03-05 | 1987-03-05 | |
| US022,096 | 1987-03-05 | ||
| US15180388A | 1988-02-03 | 1988-02-03 | |
| US151,803 | 1988-02-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1322933C true CA1322933C (en) | 1993-10-12 |
Family
ID=26695506
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000560632A Expired - Lifetime CA1322933C (en) | 1987-03-05 | 1988-03-04 | Bandmill with automatic track and strain control system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1322933C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109760146A (en) * | 2019-03-12 | 2019-05-17 | 桂林航天工业学院 | A kind of gravity tension device |
-
1988
- 1988-03-04 CA CA000560632A patent/CA1322933C/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109760146A (en) * | 2019-03-12 | 2019-05-17 | 桂林航天工业学院 | A kind of gravity tension device |
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