| JP10029111 | CIRCULAR SAW CUTTING MACHINE |
| WO/2009/151064 | CIRCULAR SAW |
| WO/1994/009707 | AUTOPSY APPARATUS |
JÖNSSON, Andreas (S- Åsbro, 690 45, SE)
| CLAIMS
1. A saw (1) being portable and/or wheeled, such as a wall saw, floor saw or masonry saw, comprising a rotatable circular saw blade (3), a drive motor (5) with an output shaft (9) for rotating the saw blade (3), and a transmission (20) for interconnecting the output shaft (9) to the rotatable saw blade (3) in order to change an unsuitable high speed and low torque combination of the output shaft (9) into a more useable lower speed and higher torque combination at the rotatable tool (3), wherein the transmission (20) comprises at least one adjustable friction saw protective clutch (30-33).
2. A saw (1) as claimed in claim 1, wherein the transmission (20) comprises two adjustable friction saw protective clutches (30-33) in parallel.
3. A saw (1) as claimed in claim 1 or 2, wherein the or both adjustable friction saw protective clutches (30-33) are adapted to be able to provide a sliding torque of at least
2 times, and preferably at least 3 times the maximum torque of the drive motor (5), and the transmission has a single fixed ratio.
4. A saw as claimed in claim 1, 2 or 3, wherein the saw comprises a toothed rack 2, intended to be fastened to, or in close proximity to, the member to be sawn, so the movable parts of the saw can move along the rack when sawing, such as a wall saw.
5. A saw as claimed in claim 1-4, wherein a first gear (22) is mounted on the output shaft (9), two gear assemblies (23) are arranged to be driven in parallel by the first gear (22), a common second gear (24) arranged to be driven by the two gear assemblies (23) in parallel, the second gear (24) having an output shaft (25), on which the saw blade (3) is intended to be mounted, each gear assembly (23) including one of said adjustable friction safety clutches (30-33).
6. A saw as claimed in claim 5, wherein a third gear (26) is mounted interposed between the gear assemblies (23) and the second gear (24) to be driven by the gear assemblies (23) and drive the second gear (24).
7. A saw as claimed in claim 5 or 6, wherein each gear assembly (23) comprises a fourth gear (27) integral with a coaxial shaft (28), a fifth gear (29) mounted to be able to rotate on the coaxial shaft (28), a friction clutch disk (30) clamped axially between the fourth gear (27) and the fifth gear (29), and a mechanism (31-34) for pressing the fifth gear (29) with an adjustable pressure against the friction clutch disk (30) to permit transfer of torque from the fifth gear (29) to the fourth gear (27).
8. A saw as claimed in claim 7, wherein a clutch transfer plate (34) is fixed on the coaxial shaft (28) between the fourth gear (27) and the friction clutch disk (30).
9. A saw as claimed in claim 7 or 8, wherein the coaxial shaft (28) has a free end extending axially from the fifth gear (29), the free end having a thread (31), a nut (32) engaging the thread (31), and a Belleville washer (33) clamped between the nut (32) and the fifth gear (29), whereby the degree of tightening of the nut (32) determines at what torque the saw blade (3) will stop rotating.
10. A saw as claimed in any one of claims 7 to 9, wherein the fifth gear (29) meshes with the first gear (22), and the fourth gear (27) meshes with the third gear (26) or with the second gear (24) which is driven by the two gear assemblies (23).
11. A saw as claimed in claim 10, wherein the first and fifth gears (22 and 29, respectively) are selected to give a speed reduction ration on the order of 3:2, and the fourth gear (27) and the third gear (26) or the second gear (24) driven thereby are selected to give a speed reduction ratio on the order of 5: 1.
12. A saw as claimed in claim 10, wherein the second and the third gears (24 and 26, respectively) are of substantially the same size.
13. A saw as claimed in any one of claims 1 to 12, wherein the transmission (20) is mounted in an arm- shaped housing (21), which can be turned on a pivotal axis that is coaxial with a rotation axis of the output shaft (9) of the motor (5).
14. A saw as claimed in any one of claim 1-13, wherein the drive motor (5) is a permanent magnet motor.
15. A saw as claimed in claim 14, wherein the permanent magnet motor (5) is arranged to perform a power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 1000 rpm.
16. A saw as claimed in claim 15, wherein the permanent magnet motor (5) is arranged to perform a power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 3000 rpm.
17. A saw as claimed in any one of claim 14-16, wherein said motor (5) also is arranged to provide the functionality of a gear box for obtaining optimal saw blade peripheral speed independently of saw blade diameter.
18. A saw as claimed in any one of claims 14-17, wherein the permanent magnet motor is arranged to perform a power output close to its maximum power output at substantially all motor rpm's between 6000 rpm and 9000 rpm, said motor (5) thereby also providing the functionality of a gear box for obtaining optimal saw blade peripheral speed independently of saw blade diameter.
19. A saw as claimed in any one of claims 14-18, wherein said motor (5) is arranged for field weakening by tapping, for obtaining a continuous maximum power output over a certain rpm-range.
20. A saw (1) having a rotatable circular saw blade (3), a drive motor (5) with an output shaft (9) for rotating the saw blade (3), and a transmission (20) for interconnecting the output shaft (9) to the rotatable saw blade (3) in order to change an unsuitable high speed and low torque combination of the output shaft (9) into a more useable lower speed and higher torque combination at the rotatable tool (3), wherein the drive motor (5) is an electric motor having an available power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 1000 rpm, and wherein said drive motor (5) at rpm's within said interval thereby also is adjustable to an rpm that via said transmission (20) transfers to an optimal rpm of the saw blade (3).
21. A saw as claimed in claim 20, wherein the drive motor (5) is a permanent magnet motor.
22. A saw as claimed in claim 21, wherein the permanent magnet motor (5) is arranged to perform a power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 1000 rpm.
23. A saw as claimed in claim 22, wherein the permanent magnet motor (5) is arranged to perform a power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 3000 rpm.
24. A saw as claimed in any one of claim 20-23, wherein said motor (5) also is arranged to provide the functionality of a gear box for obtaining optimal saw blade peripheral speed independently of saw blade diameter.
25. A saw as claimed in any one of claims 21-24, wherein the permanent magnet motor is arranged to perform a power output close to its maximum power output at substantially all motor rpm's between 6000 rpm and 9000 rpm, said motor (5) thereby also providing the functionality of a gear box for obtaining optimal saw blade peripheral speed independently of saw blade diameter.
26. A saw as claimed in any one of claims 21-25, wherein said motor (5) is arranged for field weakening by tapping, for obtaining a continuous maximum power output over a certain rpm-range. |
A SAW FOR CONSTRUCTION WORK
TECHNICAL FIELD The present invention relates to a saw being portable and/or wheeled, such as a wall saw, floor saw or masonry saw comprising a rotatable circular saw blade, a drive motor with an output shaft for rotating the saw blade, and a transmission for interconnecting the output shaft to the rotatable saw blade in order to change an unsuitable high speed and low torque combination of the output shaft into a more useable lower speed and higher torque combination at the rotatable tool.
BACKGROUND ART
Construction machinery is used in renovating, reconstructing and extending buildings, for example. Wall saws are used for cutting and extending openings for doors, windows and light wells, etc., corrective work on facades, partition walls and garden walls, etc., and controlled demolition of concrete. Floor saws are wheeled and normally used for cutting in concrete floors. Wall saws, floor saws masonry saws and similar construction machinery have a drive motor, usually electric, and a rotary tool driven by the motor. In a wall saw or floor saw, the tool is a circular saw blade equipped with cutting diamond segments. Generally, heavy duty wall saws are driven hydraulically, see US 6,955,167 B2, US 2006/0201492 Al, US 2007/0163412 Al, and US 5,887,579, for example. However, hydraulic wall saws are comparatively heavy and not easy to set up, and comparatively low-weight electric wall saws, such as the one disclosed in US 2006/0189258 Al, for example, have been introduced on the market. Such an electric wall saw is usually driven by an induction motor running at a specifically set rpm for maximum power output. The speed for maximum power output is usually in the order of magnitude between 15000 rpm and 30000 rpm requiring a planetary gear set or the like for reducing the speed to a suitable rpm for the saw blade. Planetary gears are costly and would usually require an oilpump for sufficient supply of lubrication or splash lubrication. Further, it is usually desirable to run the wall saw so that the cutting segments get an optimal peripheral speed. Saw blades of different diameters therefore requires that the transmission ratio from the induction motor to the saw blade be variable. Since the rpm for maximum power output of such an induction motor is fixed a mechanical gear box or variator is also required, e.g. a gear box with one mechanical gear for each blade diameter to be used. These solutions have several drawbacks, such as being costly, heavy, and space requiring, as well as being in need of thorough service regularly.
A wall saw usually includes a rack, i.e. a toothed bar or rod, intended to be attached to and equidistantly spaced from the wall or floor, which is to be sawed through. A carriage carries a drive motor for the circular saw blade and is movable along the rack by means of another motor. Normally the wall saw can be remotely controlled for safety and comfort of the operator. The saw blade is mounted at the free end of a pivotal arm attached to the carriage and housing a transmission for transferring the rotation of the drive motor shaft to the saw blade. The pivotal arm, or transmission housing, is swung towards or away from the wall by a third motor. The transmission usually includes a first gear mounted on the output shaft of the drive motor, and a second gear having an output shaft, on which the saw blade is intended to be mounted. The second gear may be drivingly connected to the first gear by a chain or, preferably, by one or more interposed gears. However, in case some unexpected event causes an immediate stop of the rotation of the saw blade, the wall saw and especially the teeth of its gears will be exposed to large exterior forces, and the teeth and gears have to be dimensioned to stand such forces. As it is difficult to know the size of such forces, the teeth and gears usually are greatly oversized.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a saw, in which the forces that may act on the teeth and gears of its transmission are limited and known, so that the latter do not have to be greatly oversized. Thereby also the loads the rotating parts of the motor will be reduced.
In saws of the kind referred to in the first paragraphs above, this object is achieved in that in accordance with the present invention the transmission of the saw comprises an adjustable friction saw protective clutch.
An adjustable friction clutch protects the wall saw or other construction machine against large exterior forces, and by setting the adjustable friction clutch at a desired predetermined value, a possibility to limit the maximum size of the forces that the teeth, gears and bearings are exposed to is provided. Thereby, the transmission may be made more compact and less heavy. The need for over dimensioning is hereby reduced. Advantageously, no over dimensioning is necessary, and the transmission will make out fine in rough environments.
Preferably, the transmission comprises two adjustable friction clutches in parallel. A transmission having two friction clutches will have a larger tooth engagement than a transmission having only a single friction safety clutch, and the transmission assembly can be made more compact. Still there is freedom to design the transmission so as to provide
also an arm shaped housing of a length sufficient for proper positioning of the saw blade. More specifically, the transmission preferably is mounted in an arm-shaped housing, which can be turned on a pivotal axis that is coaxial with a rotation axis of the output shaft of the motor.
In a preferred embodiment, the transmission has a first gear arranged on the output shaft, two gear assemblies mounted to be driven in parallel by the first gear, and a common second gear arranged to be driven by the two gear assemblies in parallel. The second gear has an output shaft, on which the saw blade is intended to be mounted, and each gear assembly includes one of said adjustable friction safety clutches. This design contributes to a compact structure of the transmission.
Although a drive chain might be used for transferring the rotary force to the second gear, it is recommended that a third gear is mounted interposed between the gear assemblies and the second gear to be driven by the gear assemblies and drive the second gear. Gear transmissions are more reliable than chain transmissions.
It is preferred that each gear assembly comprises a fourth gear integral with a coaxial shaft, a fifth gear mounted to be able to rotate on the coaxial shaft, a friction clutch disk clamped axially between the fourth gear and the fifth gear, and a mechanism for pressing the fifth gear with an adjustable pressure against the friction clutch disk to permit transfer of torque from the fifth gear to the fourth gear. Such a gear assembly with said adjustable friction safety clutch is compact, rugged and can easily be made to stand heavy loads.
Suitably, a clutch transfer plate is fixed on the coaxial shaft between the fourth gear and the friction clutch disk. Thereby the friction clutch disk does not have to engage an axial end face of the fourth gear.
To make the friction clutch adjustable, the coaxial shaft suitably has a free end extending axially from the fifth gear, the free end having a thread, a nut engaging the thread, and a Belleville washer clamped between the nut and the fifth gear, whereby the degree of tightening of the nut determines at what torque the saw blade will stop rotating.
Preferably, the fifth gear meshes with the first gear, and the fourth gear meshes with the gear driven by the two gear assemblies. Thereby, the transmission will be compact, rugged and can easily be made to stand heavy loads.
To achieve the compact design, the first and fifth gears may be selected to give a speed reduction ration in the order of 3:2, and the fourth gear and the gear driven thereby may be selected to give a speed reduction ratio on the order of 5:1. This results in a preferred over all speed reduction ratio in the order of 7.5: 1 from the drive motor to the rotatable tool.
The second and the third gears suitably are of substantially the same size, i.e. a gear ratio in the order of 1:1. Thereby, it will be easy to enclose the transmission in an arm-shaped housing.
In a prefered embodiment the drive motor is a permanent magnet motor. A permanent magnet motor has an advantageously high torque performance as compared to an induction motor of the same weight and size.
The permanent magnet motor can be arranged to perform a power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 1000 rpm.
Preferably, the permanent magnet motor is arranged to perform a power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 3000 rpm.
As an example the motor is arranged to perform a power output close to its maximum power output at substantially all rpm's between 6000 - 9000 rpm. This can be achieved by field weakening by tapping which is a technology known as such for permanent magnet motors and is not described in more detail in this context. However, in this particular application the field weakening by tapping results in several advantages.
The permanent magnet motor can for example be arranged to provide the functionality of a gear box for obtaining optimal saw blade peripheral speed independently of saw blade diameter. In this way the problem of keeping the peripheral speed of the saw blade constant, independently of saw blade diameter is solved and the need for a separate gear box is removed.
Another aspect of the invention is directed to a wall saw having a rotatable circular saw blade, a drive motor with an output shaft for rotating the saw blade, and a transmission for interconnecting the output shaft to the rotatable saw blade in order to transform an unsuitable high speed and low torque of the output shaft to a more useable lower speed with higher torque at the rotatable tool, wherein the drive motor is an electric motor having an
available power output close to maximum power output at substantially all rpm's within an rpm interval of at least 1000 rpm, and wherein said drive motor at rpm's within said interval thereby also is adjustable to an rpm that via said transmission transfers to an optimal rpm and/or optimal peripheral speed of the saw blade.
This aspect of the invention is also directed to a saw as defined in dependent claims 21- 26.
The permanent magnet motor for this application might preferebly be a servo motor, e.g. of the type used in industrial robots. In order to illustrate realistic figures of power outputs close to maximum power output throughout a wide rpm-range a permanent magnet motor for a wall saw according to the present invention typically has a power output of about 11 kW at 6000 rpm increasing only slightly to a power output of about 13 kW at 9000 rpm. Thereby the motor also provides the functionality of a gear box in the meaning that in order to adjust saw blade rpm it is possible to adjust the motor rpm, still maintaining a high power output close the the maximum power output. In this way the problem of keeping the peripheral speed of cutting segments of the saw blade constant, independently of saw blade diameter is solved and the need for a separate gear box is removed.
The application of field weakening by tapping reduces the risk for over heating and/or burning of the motor windings. By way of example a motor having a power output of 11 kW at 6000 rpm would if no field weakening functionality was adopted deliver just about the same output torque at 6000 rpm as at higher rpms up to 9000 rpm. This implies that the power output would be in the order of 50% higher at 9000 rpm than at 6000 rpm which would result in burning of the motor windings or else require a motor design dimensioned for much higher power output. Therefore, field weakening by tapping resolves the problem by limiting output torque at high rpm and limiting average current in motor windings at high rpm, and maintaining a generally constant power output over a wide rpm range (6000- 9000 rpm). This solution also provides a possibility to use a relatively light weight and low cost permanent magnet motor with great flexibility in a wall saw.
By using a saw protective clutch the size and weight of the transmission can be reduced. And they can be further reduced by using a permanent magnet motor. A typical wall saw as discussed above can therefore have a total weight of only 25 kg, to compare with approximately 40 kg for a corresponding conventional wall saw. This is important as the saw is carried to the work site and mounted there. Further the more compact transmission makes it possible to cut closer to the rack, closer than 190 mm, preferably closer than 170 mm, to compare with 205 mm for a corresponding conventional wall saw. This is a distinct advantage.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention will be described in more detail with reference to preferred embodiments and the appended drawings.
Fig. 1 is a perspective view of a wall saw movable along a toothed rack and having a circular saw blade driven by a motor via a transmission according to preferred embodiment of the present invention.
Fig. 2 is a perspective view of a housing of the transmission shown in Fig. 1.
Fig. 3 is a plan view of the gears and the two friction safety clutches of the transmission inside the housing.
Fig. 4 is a side view of a friction safety clutch shown in Fig. 3.
Fig. 5 is a longitudinal cross sectional view of the friction safety clutch of Fig. 4.
MODE(S) FOR CARRYING OUT THE INVENTION
Broadly, the present invention relates to a construction machine having a drive motor, a rotatable tool driven by the prime mover, and a transmission for interconnecting an output shaft of the prime mover to the rotatable tool in order to transform an unsuitable high speed and low torque of the prime mover output shaft to a more useable lower speed with higher torque at the rotatable tool. An exemplary embodiment of such a construction machine is a wall saw having a motor, a circular saw blade driven by the motor, and a transmission for interconnecting an output shaft of the motor to the rotatable saw blade. In spite of its name, a wall saw might as well be used for sawing through a floor or a ceiling.
Fig. 1 is a perspective view of a wall saw assembly, which is positioned to saw through a floor. The wall saw assembly includes a wall saw 1 that is movable along a toothed rack 2 and has a circular saw blade 3 inside a protective hood 4, and, therefore, shown in a dashed line, and driven by a motor 5 via a transmission 20 according to preferred embodiment of the present invention.
In the shown embodiment, the wall saw has two additional motors, not shown, one for moving the wall saw 1 along the toothed rack 2, which is intended to be mounted on the "wall" where an opening is to be sawed, and the other motor for raising and lowering the
saw blade 3. A cable 6 is connected to the motor 5 for supplying power to the motors and for transferring control data between a control unit, not shown, and the motors. Cooling water is fed to the motor 5 through a first hose 7, and through a second hose 8 it is passed on to a central area of the saw blade 3 to cool the saw blade and bind dust formed on
The transmission 20 includes an arm-shaped housing 21, which is best shown in Fig. 2 and has two ends. The first end is connected to an output shaft 9 of the motor 5, and the other end is connected to a shaft 25, on which the saw blade 3 is to be mounted. On raising and lowering the saw blade 3, the transmission housing 21 will be turned on a pivotal axis that is coaxial with a rotation axis of the output shaft 9 of the motor 5, and said other end of the housing, which carries the saw blade 3, will move in an arc. To permit the arcuate movement of the saw blade 3 inside the protective hood 4, the wall saw is provided with a guide arrangement 10 permitting the hood 4 a limited horizontal movement relative to the motor 5 (as seen in Fig. 1), and the hood 4 also has a vertical slot 11 that permits the shaft for the saw blade 3 to move vertically. When sawing in a vertical wall instead of a horizontal floor the permitted movement of the hood 4 relative to the motor 5 is of course vertical instead of horizontal in this embodiment of the invention.
In accordance with the present invention, the transmission comprises an adjustable friction safety clutch 30-33 (see Fig. 5). Preferably, two adjustable friction safety clutches 30-33 in parallel are used. An adjustable friction clutch protects the wall saw or other construction machine against large exterior forces, and by setting the adjustable friction clutch 30-33 at a desired predetermined value, you will limit the maximum size of the forces that the teeth and gears are exposed to. Thereby, the transmission 20 may be made more compact and less heavy. No over dimensioning is necessary, and the transmission 20 will make out fine in rough environments.
A preferred embodiment of the actual transmission inside the transmission housing 21 is shown in Fig. 3. A first gear 22 is mounted on the motor output shaft 9, which is shown as having a male spline for transferring large forces to the first gear 22 that has a matching female spline. Two gear assemblies 23 are mounted to be driven in parallel by the first gear
22, and a common second gear 24 is mounted to be driven indirectly by the two gear assemblies 23 in parallel. The second gear 24 has an output shaft 25 on which the saw blade 3 is intended to be mounted. Each gear assembly 23 includes one of said adjustable friction safety clutches. This design contributes to a compact structure of the transmission 20.
Although a drive chain might be used for transferring the rotary force to the second gear 24, it is recommended that a third gear 26 is mounted interposed between the gear assemblies 23 and the second gear 24 to be driven by the gear assemblies 23 and drive the second gear 24. Gear transmissions are more reliable than chain transmissions.
As shown in detail in Figs. 4 and 5, it is preferred that each gear assembly 23 comprises a fourth gear 27 integral with a coaxial shaft 28, a fifth gear 29 mounted to be able to rotate on the coaxial shaft 28, a friction clutch disk 30 clamped axially between the fourth gear 27 and the fifth gear 29, and a mechanism 31-33 for pressing the fifth gear 29 with an adjustable pressure against the friction clutch disk 30 to permit transfer of torque from the fifth gear 29 to the fourth gear 27. Such a gear assembly with said adjustable friction safety clutch is compact, rugged and can easily be made to stand heavy loads.
To make the friction safety clutch adjustable, the coaxial shaft 28 suitably has a free end extending axially from the fifth gear 29, the free end having a thread 31, a nut 32 engaging the thread 31, and a Belleville washer 33 clamped between the nut 32 and the fifth gear 29, whereby the degree of tightening of the nut 32 determines at what torque the saw blade 3 will stop rotating. Suitably, a clutch transfer plate 34 is fixed on the coaxial shaft 28 between the fourth gear 27 and the friction clutch disk 30. Thereby the friction clutch disk 30 does not have to engage an axial end face of the fourth gear 27. The clutch transfer plate 34 is locked against rotation on the coaxial shaft 28 in any suitable way. In the shown embodiment, the locking is accomplished by three equiangularly spaced balls 35, one of which is shown. Each ball 35 is located halfway into an individual recess in the coaxial shaft 28 and halfway into a corresponding individual recess in the clutch transfer plate 34.
The fifth gear 29 preferably meshes with the first gear 22, and the fourth gear 27 meshes with the gear driven by the two gear assemblies 23, in the shown embodiment the third gear 26 that in its turn meshes with the second gear 24. Thereby, the transmission will be compact, rugged and can easily be made to stand heavy loads. However, as will be realized, the gear assemblies 23 might as well be of a design where the first gear 22 meshes with the gear that is rotatable on the coaxial shaft 28, and the gear that is integral with the coaxial shaft 28 meshes with the third gear 26. Further, all rotatable components of the transmission are, of course, mounted in suitable bearings, well known to a person skilled in the art and not shown.
To achieve the compact design, the first and fifth gears, 22 and 29, respectively, may be selected to give a speed reduction ratio on the order of 3:2, and the fourth gear 27 and the gear driven thereby, in the shown embodiment the third gear 26, may be selected to give a
speed reduction ratio on the order of 5:1. The second and the third gears, 24 and 26, respectively, suitably are of substantially the same size. Thereby, it will be easy to enclose the transmission in an arm-shaped housing 21.
Motor 5 is a permanent magnet motor with a maximum power output of about 13 kW. 13 kW power is obtain at about 9000 rpm. The power output is kept close to maximum all the way down to 6000 rpm where the power output is about 11 kW. This is achieved by means of applying field weakening by tapping at high rpm's and thereby also reducing average current in the motor windings to prevent over heating or burning. While in this embodiment the available power output is maintained close to maximum power output in an rpm interval of 3000 rpm (between 6000-9000 rpm) it might also be suitable to provide a wall saw 1 with a motor 5 performing an available power output close to maximum power output over a wider or a narrower rpm interval, i.e. over an interval of 1000 rpm. The range of saw blade diameters to be used in a specific wall saw should be considered when adapting the field weakening of the motor 5 to provide a gear box functionality. In order to adjust saw blade rpm for optimal peripheral speed of cutting segments the rpm of the motor 5 is easily adjusted, still maintaining a power output close to the maximum power output of the motor. A permanent magnet motor with the performance described above typically has a weight of just about 8 kg.
In a further embodiment of the invention the permanent magnet motor as described in preceeding paragraph above can be provided in wall saws comprising other kinds of transmissions than those described previously. For example the parallel friction safety clutch may be omitted or replaced by any other overload protection already known in the art. More specifically, such a wall saw according to the invention comprises a rotatable circular saw blade 3, a drive motor 5 with an output shaft 9 for rotating the saw blade 3, and a transmission 20 for interconnecting the output shaft 9 to the rotatable saw blade 3 in order to transform an unsuitable high speed and low torque of the output shaft 9 to a more useable lower speed with higher torque at the rotatable tool 3, wherein the drive motor 5 is an electric motor having an available power output close to its maximum power output at substantially all rpm's within an rpm interval of at least 1000 rpm, and wherein said drive motor 5 at rpm's within said interval thereby also is adjustable to an rpm that via said transmission 20 transfers to an optimal rpm of the saw blade 3.
Hence, the problems related to the requirement of a variable transmission ratio from motor to saw blade is solved. No mechanical gear box comprising a number of different gears with fixed gear ratios for different blade diameters is required, which saves weight, cost, and service demand and increases flexibility of the wall saw. Likewise no continuously
variable transmission like a controlled planetary gear set is required. Service costs are thereby reduced, and expensive oilpump systems for sufficient supply of lubrication and splash lubrication systems can be omitted.
As compared to induction motors traditionally used in wall saws the application of a permanent magnet motor has several further advantages. In induction motors the rotor temperature reaches very high levels. High temperature and high rpm can cause problems in bearings and shaft seals which can be subject to excessive wear etc. Another important advantage of the permanent magnet motor is that it normally works with a higher torque at a relatively lower rpm than an induction motor. This reduces the speed reduction demands on the transmission.
INDUSTRIAL APPLICABILITY
The transmission of the present invention is especially applicable in wall saws and similar construction machines, where a transmission that may be made more compact and less heavy than prior art transmissions is desired. An adjustable friction safety clutch, or preferably two adjustable friction safety clutches in parallel, can be set at a desired predetermined value, so as to limit the maximum size of the forces that the teeth and gears of the transmission are exposed to. Thereby, the transmission may be made more compact and less heavy. No over dimensioning is necessary, and the transmission will make out fine in rough environments.
Providing a wall saw with a permanent magnet motor according to present invention as the drive motor for driving the saw blade via said transmission, is especially applicable for reducing weight of the motor and for gaining a generally constant power output of the motor over a wide rpm-range. Thereby, the permanent magnet motor can aslo provide the functionality of a gear box. The transmission ratio from the motor output to the saw blade is therefore fixed, i.e. fixed for a certain wall saw, but might of course be different for a different wall saw without departing from the scope of present invention. And the adjustment of saw blade rpm depending on saw blade diameter is performed by adjustment of the motor rpm, which can be made continuously if wanted. Thereby, the overall drive train can be made more compact and less heavy and more cost efficent to manufacture and maintain. A separate gear box with different gears for different saw blade diameters is for example not needed in the solution according to present invention.
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