WO2024074763A1

WO2024074763A1 - Compact belt sander

Info

Publication number: WO2024074763A1
Application number: PCT/FI2023/050565
Authority: WO
Inventors: Fredrik FORSÉN; Mikael HÄGGBLOM; Caj NORDSTRÖM
Original assignee: Mirka Ltd
Priority date: 2022-10-07
Filing date: 2023-10-03
Publication date: 2024-04-11
Also published as: FI20225908A1

Abstract

A belt sander (500) comprises: - an electric motor (MOTOR1) to cause movement of an abrasive belt (BELT1), - a thermally conductive clamp portion (CLAMP1), which is attached to the motor (MOTOR1) to conduct heat from the motor (MOTOR1), - a thermally conductive base portion (BASE1) to conduct heat from the clamp portion (CLAMP1), - a first roller (RLL1) and a second roller (RLL2) to define the position of a loop (LOOP1) of the belt (BELT1) such that the base portion (BASE1) is located between an upper portion (POR11) and a lower portion (POR12) of the loop (LOOP1), wherein the movement of the belt (BELT1) is arranged to contribute to forming one or more air flows (AIRF1) in the vicinity of the base portion (BASE1), wherein the clamp portion (CLAMP1) and the base portion (BASE1) are arranged to transfer heat from the motor (MOTOR1) to the one or more air flows (AIRF1).

Description

COMPACT BELT SANDER

FIELD

The present invention relates to a belt sander.

BACKGROUND

A belt sander may be used for sanding the surface of an object. The belt sander may be used e.g. for abrading material away from the surface.

The belt sander may comprise an electric motor, which needs to be cooled during operation. It is known that the belt sander may comprise a rotating fan for generating an air flow. The air flow may be guided through the electric motor. The electric motor may be cooled by the air flow generated by the rotating fan.

Sanding with the belt sander may generate dust particles. The air flow may carry dust particles to the electric motor. The dust particles may be deposited to the internal parts of the motor. The dust particles may cause increased wear of the motor, and/or may reduce the cooling effect of the air flow.

SUMMARY

An object of the invention is to provide a belt sander. An object is to provide a method for sanding.

According to an aspect, there is provided a device of claim 1 .

Further aspects are defined in the other claims.

The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

The belt sander comprises an elongated loop of abrasive belt. An electric motor moves the abrasive belt of the loop. The belt sander comprises an arm assembly, i.e. a "belt sword" for defining the position of the elongated loop of the abrasive belt. The belt sander is arranged to use a base portion of the arm assembly as a heat sink for cooling the electric motor. Using the base portion as the heat sink may improve cooling efficiency of the electric motor without using a conventional fan.

The base portion is located inside the loop of the abrasive belt, between an upper portion and a lower portion of the loop of the abrasive belt. The upper portion of the loop and the base portion may define a first gap. The lower portion of the loop and the base portion may define a second gap. The moving belt may induce air flows in the gaps between the belt and the base portion. The thermally conductive base portion may be arranged to transfer heat to the induced air flows.

The arm assembly may be attached to the motor by using a thermally conductive clamp. At least the base element of the arm assembly may operate as a heat sink, to transfer heat from the motor to at least one air flow generated by the moving abrasive belt.

In an embodiment, no conventional rotating fan is used, but the abrasive belt itself causes movement of air close to the arm assembly. The heat may be effectively transferred via the arm assembly to the air flow. The belt sander may be implemented such that it does not comprise a rotating fan for cooling the motor. Cooling the motor with the base portion instead of using a rotating fan may allow simplifying the construction of the belt sander. The belt sander may be implemented as a compact device. Cooling the motor with the base portion instead of using a rotating fan may allow reducing the number of the parts of the device. The fanless structure may also provide additional freedom to implement the belt sander as an ergonomic power tool. The electric motor of the belt sander may be a sealed electric motor. The motor may be encapsulated such that ambient air is not circulated through the motor. The motor may be encapsulated such that harmful dust particles cannot enter into the motor. The electric motor may be sealed e.g. such that particles larger than 5 Lim are substantially prevented from entering into the motor. The motor may be e.g. a brushless electric motor. The motor may be e.g. a brushless direct current motor. The belt sander may be suitable for professional use, e.g. in a dusty environment. The belt sander may have a sealed dust-proof mechanical structure. Consequently, the belt sander may have long operating lifetime.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following examples, several variations will be described in more detail with reference to the appended drawings, in which

Fig. 1a shows, by way of example, in a side view, a belt sander,

Fig. 1 b shows, by way of example, in a cross-sectional top view, the belt sander,

Fig. 2a shows, by way of example, in a side view, transferring heat from the motor to induced air flows,

Fig. 2b shows, by way of example, in a cross-sectional top view, transfer of heat from the motor to induced air flows,

Fig. 2c shows, by way of example, in a side view, dimensions of the base portion,

Fig. 2d shows, by way of example, in a cross-sectional top view, dimensions of the base portion, and dimensions of the clamp portion, Fig. 2e shows, by way of example, in a top view, the abrasive belt mounted on the rollers,

Fig. 3a shows, by way of example, in a three-dimensional view, a belt sander,

Fig. 3b shows, by way of example, in a three-dimensional view, a belt sander,

Fig. 4 shows, by way of example, in a side view, a belt sander device implemented as a handheld device,

DETAILED DESCRIPTION

Referring to Figs. 1a and 1 b, the belt sander 500 may comprise:

- an electric motor MOTOR1 to cause movement of an abrasive belt BELT1 ,

- a clamp portion CLAMP1 attached to the motor MOTOR1 ,

- a base portion BASE1 attached to the clamp portion CLAMP1 ,

- a first roller RLL1 and a second roller RLL2 to define the position of a loop LOOP1 of the belt BELT1 such that the base portion BASE1 is located inside the loop LOOP1 .

The moving belt BELT1 may induce one or more air flows AIRF1 by causing movement of ambient air AIR1 (Figs. 2a, 2b). The moving belt BELT1 may contribute to forming one or more air flows AIRF1 in the vicinity of the base portion BASE1. The temperature TIN of the ambient air AIR1 may be substantially lower than the temperature TMOTOR of the housing CYL1 of the motor MOTOR1. The portions CLAMP1 , BASE1 may be arranged to transfer heat from the motor MOTOR1 to the induced air flows AIRF1. The clamp portion CLAMP1 , the base portion BASE1 , and the air flows AIRF1 may be arranged to cool the motor MOTOR1 .

The belt sander 500 may comprise the abrasive belt BELT1 during operation. The belt sander 500 may comprise the first roller RLL1 and the second roller RLL2 to define the position of the loop LOOP1 of the belt BELT1. The first roller RLL1 may operate as a driving roller. The motor MOTOR1 may rotate the first roller RLL1. The roller RLL1 may transfer mechanical power of the motor MOTOR1 to the abrasive belt BELT1 . The motor MOTOR1 may rotate the roller RLL1 , which in turn may move the belt BELT1. A shaft SHF1 of the motor MOTOR1 may drive the first roller RLL1. The first roller RLL1 may be e.g. attached to the shaft SHF1 .

The belt sander 500 may comprise an arm assembly SWORD1 to define the position of the second roller RLL2. The arm assembly may also be called e.g. as the belt sword.

The arm assembly SWORD1 may comprise the second roller RLL2, a tracking control mechanism TRAC1 , a tensioning mechanism TEN1 , the base portion BASE1 and the clamp portion CLAMP1 .

The first roller RLL1 may also be called e.g. as a drive roller. The second roller RLL2 may also be called e.g. as tensioning roller.

The clamp portion CLAMP1 may mechanically and thermally connect the arm assembly SWORD1 to the motor MOTOR1 .

The clamp portion CLAMP1 may at least partly surround the motor MOTOR1 . The clamp portion CLAMP1 may comprise a heat transfer surface SRF1 for transferring heat from the motor MOTOR1. The shape of the heat transfer surface SRF1 may match the shape of the housing CYL1 of the motor MOTOR1 , so as to effectively transfer heat via the surface SRF1 . For example, the housing CYL1 of the motor MOTOR1 may be cylindrical, and the clamp portion CLAMP1 may comprise a matching cylindrical surface portion SRF1.

The heat transfer surface SRF1 may be compressed against the housing of the motor MOTOR1 , so as to effectively transfer heat. For example, a clamp portion CLAMP1 having a circular inner surface may be tightened around the motor MOTOR1 by one or more screws SCRW1 . The clamp portion CLAMP1 may comprise an adjustment slit SLIT1 so that rotation of the tightening screw SCRW1 may change the inner dimension of the clamp portion CLAMP1. Sufficient compression may also be provided e.g. by one or more springs. The belt sander may comprise one or more springs to compress the clamp portion CLAMP1 against the housing of the motor. The clamp portion CLAMP1 itself may be arranged to operate as a pre-tensioned elastic spring, which squeezes the housing of the motor.

The clamp portion CLAMP1 may thermally couple the motor MOTOR1 to the base portion BASE1 . The device 500 may transfer heat from the clamp portion CLAMP1 to the base portion BASE1 via a cross-sectional area CR1. The clamp portion CLAMP1 and the base portion BASE1 may be portions of the same piece (ELE1 ) or separable pieces (CLAMP1 , BASE1 ).

Implementing the clamp portion CLAMP1 and the base portion BASE1 as portions of the same arm element ELE1 may ensure rigid structure and efficient heat transfer from the clamp portion CLAMP1 to the base portion BASE1 .

Providing the clamp portion CLAMP1 and the base portion BASE1 as different pieces may e.g. allow implementing the tracking mechanism TRAC1 and/or the tensioning mechanism TEN1 near the clamp portion CLAMP1 .

Providing the clamp portion CLAMP1 and the base portion BASE1 as different pieces may allow simplifying the shape of the portions CLAMP1 , BASE1 , which may e.g. reduce manufacturing costs for short run production.

The tensioning mechanism TEN1 may maintain a suitable tension of the belt BELT 1 . The tensioning mechanism TEN1 may be arranged to push the second roller RLL2 e.g. in the direction SX away from the first roller RLL1. The tensioning mechanism TEN1 may comprise e.g. a first arm element 51 , which is arranged to slide with respect to the base portion BASE1. The tensioning mechanism TEN1 may comprise a spring SPR1 for causing a tensioning force. The tensioning mechanism TEN1 may comprise a sliding joint. The tensioning mechanism TEN1 may also be called e.g. as a tensioning joint.

The tracking control mechanism TRAC1 may control orientation of the axis AX2 of the second roller RLL2 with respect to the axis AX1 of the first roller RLL1. The belt "tracking" means keeping the belt BELT1 in a suitable transverse position in the direction SZ with respect to the rollers RLL1 , RLL2. The belt tracking may be adjusted so as to prevent the moving belt from falling away from the rollers RLL1 , RLL2. The tracking control mechanism TRAC1 may comprise e.g. a holder 53 for holding the second roller RLL2. The holder 53 may pivot about a pivot axis AX3 with respect to a second arm element 52. The angular orientation of the holder 53 may be set e.g. by an adjustment screw SCRW2. The holder and the roller RLL2 may pivot about the axis AX3 by e.g. rotating the adjustment screw SCRW2. The second arm element 52 may be fixed to the first arm element 51 .

The arm assembly SWORD1 may optionally comprise a shoe SHOE1 for providing additional internal support for the moving belt BELT1.

SX, SY and SZ denote orthogonal directions. The axis AX1 of the first roller RLL1 may be parallel with the direction SZ. The tensioning mechanism TEN1 may push the second roller RLL2 in the direction SX. The pivot axis AX3 may be parallel with the direction SY.

The motor may be e.g. a brushless electric motor. The belt sander may have a sealed dust-proof mechanical structure. The motor MOTOR1 may be sealed against dust. The motor MOTOR1 may be enclosed such that ambient air AIR1 is not circulated through the motor MOTOR1 during operation, so as to reduce or prevent dust from entering into the motor MOTOR1. For example, the housing CYL1 of the motor MOTOR1 may prevent dust from entering into the motor MOTOR1 . For example, a housing HOLI1 of the sander device 500 may be prevent dust from entering into the motor MOTOR1 . The motor MOTOR1 may optionally comprise one or more sealed bearings to prevent dust from entering into the motor MOTOR1 .

Referring to Figs. 2a and 2b, the motor MOTOR1 converts a first fraction T|M ‘ PELEC,IN of electrical input power PELEC.IN into the mechanical rotational movement of the motor shaft SHF1 , wherein the remaining fraction (1 - T|M)- PELEC.IN of the electrical input power is converted into heat. The heat generated in the motor is transferred away from the motor, so as to prevent overheating of the motor. The symbol qo denotes the total rate of heat flow generated by the electric motor MOTOR1. For example, the efficiency T|M of the motor MOTOR1 may be 85%, and the input electric power PELEC.IN may be 100 W. In that example case, the mechanical output power of the motor MOTOR1 is T|M ’ 100 W = 85 W, and the total rate qo of heat flow is (100%-T|M)- 100 W = 15 W. The total rate qo of heat flow of the motor MOTOR1 may also be called e.g. as the thermal output power of the motor.

The rate of heat flow means the flow of heat (J) per unit time (s). The unit of heat is J (Joule). The unit of the rate (qo, qi , q2, qs, q4A, q4B, qs, qe,qc) of heat flow is W (watt). The rate of heat flow means the amount of heat that is transferred through a cross-sectional area per unit of time.

The thermal output power qo of the motor may be distributed and dissipated e.g. via the clamp portion CLAMP1 , via an exposed surface of the motor, and/or via a housing HOLI1 of the sander device 500. qc may denote a rate of heat flow dissipated via a housing HOLI1 of the sander device 500. The housing HOLI1 of the belt sander is shown e.g. in Fig. 4.

According to the present method, at least a significant fraction of the total rate qo of heat flow is conducted via the clamp portion CLAMP1 and via the base portion BASE1 to the one or more air flows AIRF1 induced by the movement of the belt BELTI .

The base portion BASE1 is located between an upper portion POR11 of the loop LOOP1 and a lower portion POR12 of the loop LOOP1 of the belt BELT 1 . The upper portion POR11 of the loop LOOP1 and the base portion BASE1 may define a first air gap GAP11 .

The lower portion POR12 of the loop LOOP1 and the base portion BASE1 may define a second air gap GAP12. The moving abrasive belt BELT1 may cause air flows in the vicinity of the base portion BASE1 .

The moving abrasive belt BELT1 may contribute to forming an air flow AIRF1 in the first air gap GAP11 and/or the moving abrasive belt BELT1 may contribute to forming an air flow AIRF1 in the second air gap GAP12. The moving abrasive belt BELT1 may cause an air flow AIRF1 in the first gap GAP1 1 and/or the moving abrasive belt BELT1 may cause an air flow AIRF1 in the second gap GAP12.

The motor MOTOR1 may generate heat during operation. The base portion BASE1 may be arranged to operate as a heat sink for transferring heat from the motor MOTOR1 to the air flows AIRF1. The base portion BASE1 may transfer heat to the air flow AIRF1 in the first gap GAP11 and/or to the air flow AIRF1 in the second gap GAP12.

The moving belt BELT 1 may contribute to forming one or more air flows AIRF1 . The moving belt BELT1 may cause one or more air flows AIRF1. In an embodiment, the sander device 500 does not comprise a rotating fan, and the one or more air flows AIRF1 may be caused mainly by the moving belt BELT 1 .

The belt BELT1 may move at a velocity VB. The velocity VB may be e.g. in the range of 5 m/s to 50 m/s during normal operation of the belt sander 500. The motor speed and the velocity VB may be adjustable. The maximum velocity VB during operation of the belt sander 500 may be e.g. in the range of 5 m/s to 50 m/s. The cooling effect of the airflows induced by the moving belt may increase with increasing velocity of the belt.

The first roller RLL1 may rotate at an angular velocity coi . The second roller RLL2 may rotate at an angular velocity C02.

TMOTOR may denote the maximum temperature of the housing CYL1 of the motor MOTOR1 . The sander device 500 may be arranged to operate such that the temperature TMOTOR remains e.g. lower than 80°C, so as to reduce the risk of damaging the motor, and/or in order to increase operating lifetime of the motor.

TIN denotes the initial temperature of the air of the air flows AIRF1 . The initial air temperature TIN may be e.g. in the range of 10°C to 30°C, as determined by the temperature of the ambient air AIR1 . TBASE denotes a temperature of the base portion BASE1 . The clamp portion CLAMP1 and the base portion BASE1 may together form a thermal path from the housing of the motor MOTOR1 to the air flows AIRF1 caused by the movement of the belt BELT1 at the velocity VB.

The clamp portion CLAMP1 may receive heat from the housing of the motor MOTOR1 at the rate qi. The base portion BASE1 may receive heat from the clamp portion CLAMP1 by conduction at the rate q2. The base portion BASE1 may receive heat from the clamp portion CLAMP1 by conduction via the cross- sectional area CR1 between said portions CLAMP1 , BASE1 . The base portion BASE1 may internally conduct heat at a rate qs. The base portion BASE1 may transfer heat to the air flows AIRF1 by forced convection.

An upper surface SRF11 of the base portion BASE1 may face the upper portion POR11 of the loop LOOP1 of the belt BELT1. The upper portion POR11 and the upper surface SRF11 may define an air gap GAP11. The upper surface SRF11 of the base portion BASE1 may transfer heat to an air flow AIRF1 in the gap GAP11 by forced convection at a rate q4A.

A lower surface SRF12 of the base portion BASE1 may face the lower portion POR12 of the loop LOOP1 of the belt BELT1. The lower portion POR12 and the lower surface SRF12 may define an air gap GAP12. The lower surface SRF12 of the base portion BASE1 may transfer heat to an air flow AIRF1 in the gap GAP12 by forced convection at a rate q4B.

At least a significant relative fraction (q2/qo) of the heat generated by motor may be transferred to the air flows AIRF1 via the base portion BASE1. The materials and the geometry of the portions CLAMP1 , BASE1 may determine the thermal coupling from the motor to the base portion BASE1 , and further from the base portion BASE1 to the air flows AIRF1. The materials and the geometry of the portions CLAMP1 , BASE1 may be selected such that the fraction (q2/qo) of heat flow coupled via the base portion BASE1 may be e.g. greater than 30%, greater than 50%, greater than 80%, or even greater than The motor may generate heat at a first rate qo of heat flow. The arm assembly SWORD1 may thermally couple the motor to the induced air flows AIRF1 . The base portion BASE1 may receive heat at a second rate q2 of heat flow. The materials and the geometry of the portions CLAMP1 , BASE1 may be selected such that the ratio of the second rate q2 to the first rate qo may be e.g. greater than 30%, greater than 50%, greater than 80% or even greater than 90%. A major fraction of the heat generated by the motor may be dissipated via the base portion BASE1 to the induced air flows AIRF1. In an embodiment, the dimensions of the base portion and the dimensions of the clamp portion are selected such that almost all heat generated by the motor may be dissipated via the base portion BASE1 to the induced air flows AIRF1.

The clamp portion CLAMP1 and the base portion BASE1 may be made from a material, which has high thermal conductivity, e.g. aluminum alloy or magnesium alloy. Thermal conductivity of the material of the clamp portion CLAMP1 may be e.g. higher than 100 Wnr¹K’¹. Thermal conductivity of the material of the base portion BASE1 may be e.g. higher than 100 Wnr¹K’¹.

For example, the clamp portion CLAMP1 and the base portion BASE1 may be arranged to transfer heat from the motor MOTOR1 to the air flows AIRF1 such that a rate of heat flow q2 via the base portion BASE1 is e.g. greater than 30%, greater than 50%, greater than 80% or even greater than 90% of the rate qo, in a situation where a speed (VB) of the belt (BELT1 ) is greater than 5 m/s, a temperature (TMOTOR) of the motor (MOTOR1 ) is greater than 50°C, and the temperature (TIN) of ambient air (AIR1 ) is lower than 30°C.

The surface SRF11 and/or SRF12 may be smooth in order to reduce or avoid deposition of dust on the surface SRF11 and/or SRF12.

Alternatively, the surface SRF11 and/or SRF12 may be e.g. ribbed, in order to increase effective heat transfer area. The ribbed heat transfer surface may provide more efficient cooling in an operating condition or conditions where dust is not significantly deposited on the grooves of the ribbed heat transfer surface. Also other surfaces of the device 500 may be exposed to the air flows AIRF1 , which are induced by the moving belt BELT1. For example, a fraction of the heat of the motor may be transferred to the air flows AIRF1 also via other surfaces of the base portion BASE1 , in addition to the surfaces SRF11 , SRF12.

In an embodiment, a heat flow qs may be optionally transferred from the base portion BASE1 to one or more arm elements 51 , 52 via the tensioning mechanism TEN1 . The arm elements 51 , 52 may transfer heat flow qe to the air flows AIRF1 by forced convection. The tensioning joint TEN1 may be thermally conductive so as to further improve cooling of the motor.

Figs. 2c and 2d show dimensions of the base portion BASE1 and dimensions of the clamp portion CLAMP1. The base portion BASE1 may have a length LBASEI in the longitudinal direction SX, a width WBASEI in the transverse direction SZ, and a height hBASEi in the vertical direction SY. The clamp portion CLAMP1 may have a thickness dcLAMPi in the longitudinal direction SX, and a width WCLAMPI in the transverse direction SZ. di2 denotes the height of the air gap GAP12. di 1 denotes the height of the air gap GAP11 .

The heat of the motor may be conducted from the clamp portion CLAMP1 to the base portion BASE1 via a common cross-sectional area CR1 of the clamp portion CLAMP1 and the base portion BASE1. The height of the cross- sectional area CR1 may be e.g. substantially equal to the height IIBASEI , and/or the length of the cross-sectional area CR1 may be e.g. substantially equal to the thickness dcLAMPi .

The dimensions of the base portion BASE1 and the dimensions of the clamp portion CLAMP1 have an effect on the heat transfer from the motor MOTOR1 to the air flow AIRF1.

To the first approximation, the area of a lower convective surface SRF12 in the gap GAP12 may be substantially equal to the length LBASEI multiplied by the width WBASEI . Said convective surface SRF12 may convectively transfer heat from the base portion BASE1 to the air flow AIRF1 in the gap GAP12. To the first approximation, the area of an upper convective surface SRF11 in the gap GAP11 may be substantially equal to the length LBASEI multiplied by the width WBASEI . Said convective surface SRF11 may convectively transfer heat from the base portion BASE1 to the air flow AIRF1 in the gap GAP11 .

The base portion BASE1 may conduct heat from the clamp portion CLAMP1 to the lower convective surface SRF12 and/or to the upper convective surface SRF1 1 . The base portion BASE1 may receive heat via the area CR1 , and the base portion BASE1 may conduct the received heat to the surfaces SRF12, SRF11.

The gap height du may be e.g. in the range of 1 mm to 20 mm. The gap height di2 may be e.g. in the range of 1 mm to 20 mm. If the gap height is too small, then the temperature of the air may rise in the gap so that the cooling effect is reduced. If the gap height is too large, then the effective velocity of air in the vicinity of the heat transfer surface may be reduced.

The thickness dcLAMPi may be e.g. in the range of 5 mm to 30 mm, so as to provide efficient conduction of heat from the motor to the base portion.

The length LBASEI may be e.g. in the range of 50 mm to 500 mm. The width WBASEI may be e.g. in the range of 5 mm to 50 mm.

The area of the upper heat transfer surface SRF11 of the base portion BASE1 may be e.g. greater than 5 cm², greater than 10 cm², or even greater than 20 cm², in order transfer heat to the air flow AIRF1 at a sufficient rate q4A.

The rate q4A of heat flow transferred via the upper surface SRF11 to the air flow AIRFI may be e.g. greater than 5 W, greater than 10 W, or even greater than 20 W.

The dimensions (LBASEI , WBASEI , hBASEi) of the base portion BASE1 and the dimensions (dcLAMPi, WCLAMPI ) of the clamp portion CLAMP1 may be selected e.g. such that the rate q4A of heat flow transferred via the upper surface SRF11 to the air flow AIRFI may be e.g. greater 15%, greater than 25%, greater than 40%, or even greater than 45% of the rate qo of heat flow generated by the motor MOTOR1.

In an embodiment, the rate q4A of heat flow transferred via the upper surface SRF1 1 to the air flow AIRF1 in the gap GAP11 may be substantially equal to the rate q4B of heat flow transferred via the lower surface SRF12 to the air flow AIRF1 in the gap GAP12.

The dimensions (LBASEI , WBASEI , hBASEi) of the base portion BASE1 and the dimensions (dcLAMPi, WCLAMPI ) of the clamp portion CLAMP1 may be selected e.g. such that a rate of heat flow (q2) transferred from the motor (MOTOR1 ) via the base portion (BASE1 ) is greater than 30% of a total rate of heat flow (qo) generated by the motor (MOTOR1 ) in a situation where a speed (VB) of the belt (BELT1 ) is greater than 5 m/s, a maximum temperature (TMOTOR) of the housing of the motor (MOTOR1 ) is greater than 50°C, and the temperature (TIN) of ambient air (AIR1 ) is lower than 30°C.

Fig. 2e shows, by way of example, the abrasive belt BELT1 mounted on the rollers RLL1 , RLL2. The abrasive belt BELT1 has a width WBELTI .

Figs. 3a and 3b show, by way of example, in a three-dimensional view, the arm assembly SWORD1. The arm assembly SWORD1 may optionally comprise a protective external guard SHD1 , e.g. to prevent the user from accidentally touching the moving belt BELT1 .

A fraction of the heat of the motor may be optionally transferred to ambient air via one or more other thermal paths, in addition to the base portion. For example, the belt sander 500 may comprise an external guard SHD1 , and a fraction of the heat of the motor may be transferred to one or more air flows AIRF1 via the external guard. The moving belt BELT1 may induce an air flow also in the vicinity of the guard SHD1 , and heat generated by the motor MOTOR1 may be transferred via the guard SHD1 to the airflow AIRF1 induced by the moving belt BELT1 .

In an embodiment, a first partial heat flow of the motor MOTOR1 may be transferred via the clamp portion CLAMP1 and the base portion BASE1 to induced air flows AIRF1 , and a second partial heat flow of the motor MOTOR1 may be transferred via the clamp portion CLAMP1 and the guard SHD1 to an induced air flow.

In an embodiment, heat generated by the motor MOTOR1 may be transferred also via one or more arm elements 51 , 52. A part of the heat may be conducted from the base portion BASE1 to the arm elements 51 , 52 e.g. via the tensioning joint TEN1 .

For example, the rate qs of heat flow transferred from the base portion BASE1 via the tensioning joint TEN1 may be greater than 10% of the total rate qo of heat flow generated by the motor MOTOR1 in a situation where a speed (VB) of the belt (BELT1 ) is greater than 5 m/s, a maximum temperature (TMOTOR) of the housing of the motor (MOTOR1 ) is greater than 50°C, and the temperature (TIN) of ambient air (AIR1 ) is lower than 30°C.

Referring to Fig. 4, the control system of the belt sander 500 may comprise e.g. a user interface LIIF1 , a control unit CNT1 , and/or a driving unit DRV1 .

The device 500 may comprise a driving unit DRV1 for converting DC electrical power or AC mains power into driving currents. DC means direct current. AC means alternating current. The driving unit DRV1 may receive electric power via conductors W1 , W2. The device 500 may receive operating power e.g. from a battery BAT1 and/or from the mains network. The device 500 may comprise the battery BATI . The driving currents formed by the driving unit DRV1 may be conducted to the motor MOTOR1 via conductors W3A, W3B, W3C. The driving unit DRV1 may form currents for driving a brushless electric motor MOTOR1.

The device 500 may comprise a user interface LIIF1 for receiving user input from a user. The user interface LIIF1 may be e.g. a push button or a rocker switch.

The device 500 may comprise a control unit CNT1 for controlling operation of the motor MOTOR1 based on user input received via the user interface LIIF1 and/or for controlling operation of the motor MOTOR1 based on a control signal obtained from a sanding robot system. The control unit CNT1 may send a control signal S1 to the driving unit DRV1 . The driving unit DRV1 may form driving currents for the motor MOTOR1 according to the control signal S1 . The control signal S1 may be e.g. a digital signal or an analog signal. The control unit CNT1 may be e.g. an electrical switch or a potentiometer, which may be coupled to the push button LIIF1. Pushing of the button LIIF1 may e.g. start operation of the motor MOTOR1 at an operating speed, and releasing the button may stop operation of the motor. In an embodiment, the rotation speed of the motor MOTOR1 may be proportional to the position of the push button UIF1.

The belt sander 500 may optionally comprise a housing HOUS1 for protecting one or more parts (e.g. MOTOR1 , LIIF1 , CNT1 , DRV1 ).

The belt sander 500 may optionally comprise a handle GRIP1 for using the device as a handheld device. For example, a portion of the housing HOUS1 may be arranged to operate as a handle GRIP1 .

The belt sander 500 may also be implemented without the handle GRIP1 . For example, the belt sander 500 may be attached to a robot.

The belt sander may be e.g. a cordless power tool. The motor may be powered by a battery and/or by the mains power network.

The belt sander 500 may be delivered to a user with or without the abrasive belt BELT1 . The belt sander 500 may comprise the abrasive belt BELT1 during operation. The user may place the belt BELT1 on the belt sander 500 before operation. The abrasive belt BELT1 may comprise abrasive grains AG1 attached to a flexible supporting layer SLIP1 . The abrasive belt BELT1 may be an endless belt. The grit size of the abrasive grains AG1 may be e.g. in the range of 40 to 1000 according to the FEPA standard. The size of the abrasive grains may be e.g. in the range of 5 m to 500 pm, corresponding to the selected grit size.

The width WBELTI of the abrasive belt BELT1 may be e.g. in the range of 5 mm to 50 mm (in the direction SZ). In an embodiment, the device may be implemented as a narrow belt sander. The width WBELTI of the abrasive belt may be e.g. smaller than 20 mm. The belt sander may be used e.g. for sanding a part of an automobile. The belt sander may be used e.g. when a metallic panel is replaced in a collision repair. The belt sander may be used e.g. for grinding away spot welds, which join the panel to the automotive body, thereby making it possible to separate the panel from the automotive body.

The belt sander comprising a narrow belt may be called e.g. as a filing sander.

In an embodiment, the belt sander may be implemented without a rotating fan, e.g. in order to provide a simple dust-proof construction.

In an embodiment, the belt sander may comprise a rotating fan e.g. for additional cooling of the motor. The rotating fan may be coupled e.g. to the shaft of the motor MOTOR1 and/or to the first roller RLL1. For example, the fan may contribute to forming an additional air flow in the vicinity of the clamp portion CLAMP1 and/or in the vicinity of the external guard SHD1. However, also in that case the moving abrasive belt BELT1 may cause significant air flows AIRF1 in the gaps GAP12, GAP11 between the belt loop LOOP1 and the base portion BASE1 . Air flows AIRF1 in the gaps GAP12, GAP11 may be caused mainly by the moving belt BELT1. Heat transfer via the base portion BASE1 to airflows AIRF1 generated by the moving belt may be significant also when the belt sander comprises a rotating fan.

The term "fan" means herein a rotating element, which comprises at least three blades and/or vanes to cause an air flow.

The electric motor may directly rotate the first roller RLL1 without using a gearbox. The first roller RLL1 may be attached to the shaft SHF1 of the motor MOTOR1 such that the first roller RLL1 rotates together with the shaft SHF1 . The first roller RLL1 may be directly attached to the shaft SHF1 . The rotation speed of the first roller RLL1 may be equal to the rotation speed of the rotor of the electric motor MOTOR1 . Implementing the belt sander without a gearbox may provide e.g. mechanically simple structure and/or high efficiency for transferring power of the motor to the belt.

Alternatively, the electric motor M0T0R1 may rotate the first roller RLL1 by using a gearbox such that the rotation speed of the first roller RLL1 is different from the rotation speed of the rotor of the electric motor M0T0R1 .

In an embodiment, the orientation of the arm assembly may be adjustable. The belt sander may have a pivotable arm assembly.

The belt sander may comprise the abrasive belt, but the belt sander may also be stored and/or delivered without the abrasive belt. The belt sander does not need to comprise the belt when delivered to a user. The user may subsequently mount the abrasive belt on the belt sander before use. The belt may be a replaceable part of the belt sander. A method for abrading may comprise mounting a first abrasive belt on the belt sander, abrading an object with the first abrasive belt mounted on the belt sander, replacing the first abrasive belt with a second abrasive belt, and abrading the object with the second abrasive belt mounted on the belt sander. The first abrasive belt may comprise first abrasive grains, and the second abrasive belt may comprise second abrasive grains. The grit size of the first abrasive grains may be same as or different from the grit size of the second abrasive grains.

For the person skilled in the art, it will be clear that modifications and variations of the devices and methods according to the present invention are perceivable. The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.

Claims

1 . A belt sander device (500), comprising:

- an electric motor (MOTOR1 ) to cause movement of an abrasive belt (BELT 1 ),

- a thermally conductive clamp portion (CLAMP1 ), which is attached to the motor (MOTOR1 ) to conduct heat from the motor (MOTOR1 ),

- a thermally conductive base portion (BASE1 ) to conduct heat from the clamp portion (CLAMP1 ),

- a first roller (RLL1 ) and a second roller (RLL2) to define the position of a loop (LOOP1 ) of the belt (BELT1 ) such that the base portion (BASE1 ) is located between an upper portion (POR11 ) and a lower portion (POR12) of the loop (LOOP1 ), wherein the movement of the belt (BELT1 ) is arranged to contribute to forming one or more air flows (AIRF1 ) in the vicinity of the base portion (BASE1 ), wherein the clamp portion (CLAMP1 ) and the base portion (BASE1 ) are arranged to transfer heat from the motor (MOTOR1 ) to the one or more air flows (AIRF1 ).

2. The device (500) of claim 1 , wherein the base portion (BASE1 ) has at least a first surface (SRF11 ) for transferring heat from the base portion to an air flow (AIRF1 ) by forced convection, wherein the first surface (SRF11 ) faces the upper portion (POR11 ), wherein the surface area of the first surface (SRF11 ) is greater than 5 cm².

3. The device (500) of claim 1 or 2, wherein the dimensions of the clamp portion (CLAMP1 ) and the base portion (BASE1 ) are selected such that a rate (q2) of heat flow transferred from the motor (MOTOR1 ) via the base portion (BASE1 ) is greater than 30% of a total rate of heat flow (qo) generated by the motor (MOTOR1 ) in a situation where a speed (VB) of the belt (BELT1 ) is greater than 5 m/s, a maximum temperature (TMOTOR) of the housing of the motor (MOTOR1 ) is greater than 50°C, and the temperature (TIN) of ambient air (AIR1 ) is lower than 30°C.

4. The device (500) according to any of the claims 1 to 3, wherein the motor (MOTOR1 ) has a cylindrical housing (CYL1 ), the clamp portion (CLAMP1 ) comprises a cylindrical heat transfer surface (SRF1 ) for transferring heat from the motor (MOTOR1 ), and the shape of the heat transfer surface (SRF1 ) matches the shape of the housing (CYL1 ) of the motor MOTOR1 so as to effectively transfer heat via the heat transfer surface (SRF1 ).

5. The device (500) according to any of the claims 1 to 4, wherein the clamp portion (CLAMP1 ) at least partly surrounds a housing (CYL1 ) of the motor (MOTOR1 ).

6. The device (500) according to any of the claims 1 to 5, wherein thermal conductivity of the material of the clamp portion (CLAMP1 ) is greater than 100 Wm-'K’¹.

7. The device (500) according to any of the claims 1 to 6, wherein the base portion (BASE1 ) and the clamp portion (CLAMP1 ) are portions of the same piece.

8. The device (500) according to any of the claims 1 to 7, wherein the motor (MOTOR1 ) is enclosed such that ambient air (AIR1 ) is not circulated through the motor (MOTOR1 ) during operation.

9. The device (500) according to any of the claims 1 to 8, wherein the width (WBELTI ) of the belt (BELT 1 ) is in the range of 5 mm to 50 mm.

10. The device (500) according to any of the claims 1 to 9, wherein the first roller (RLL1 ) is directly attached to a shaft (SHF1 ) of the motor (MOTOR1 ).

11 . The device (500) according to any of the claims 1 to 10, wherein the second roller (RLL2) is mechanically connected to the base portion (BASE1 ) via a tension ing joint (TEN 1 ), wherein rate of heat flow (qs) transferred from the base portion (BASE1 ) via the tensioning joint (TEN 1 ) is greater than 10% of the total rate of heat flow (qo) generated by the motor (MOTOR1 ) in a situation where a speed (VB) of the belt (BELT 1 ) is greater than 5 m/s, a maximum temperature (TMOTOR) of the housing of the motor (MOTOR1 ) is greater than 50°C, and the temperature (TIN) of ambient air (AIR1 ) is lower than 30°C.

12. A method for sanding with a belt sander (500), the belt sander (500) comprising: - an electric motor (MOTOR1 ) to cause movement of an abrasive belt (BELT 1 ),

- a first roller (RLL1 ) and a second roller (RLL2) to define the position of a loop (LOOP1 ) of the belt (BELT1 ) such that the base portion (BASE1 ) is located between an upper portion and a lower portion of the loop (LOOP1 ), the method comprising:

- operating the motor (MOTOR1 ) such that the movement of the belt (BELT 1 ) contributes to forming air flows (AIRF1 ) in the vicinity of the base portion (BASE1 ), and

- transferring heat from the motor (MOTOR1 ) to the air flows (AIRF1 ) via the clamp portion (CLAMP1 ) and via the base portion (BASE1 ).

13. The method of claim 12, wherein the dimensions of the clamp portion (CLAMP1 ) and the base portion (BASE1 ) have been selected such that a rate of heat flow (q2) transferred from the motor (MOTOR1 ) via the base portion (BASE1 ) is greater than 30% of a total rate of heat flow (qo) generated by the motor (MOTOR1 ) in a situation where a speed (VB) of the belt (BELT1 ) is greater than 5 m/s, a maximum temperature (TMOTOR) of the housing of the motor (MOTOR1 ) is greater than 50°C, and the temperature (TIN) of ambient air (AIR1 ) is lower than 30°C.

14. The method of claim 12 or 13, wherein the motor (MOTOR1 ) has a cylindrical housing (CYL1 ), the clamp portion (CLAMP1 ) comprises a cylindrical heat transfer surface (SRF1 ) for transferring heat from the motor (MOTOR1 ), and the shape of the heat transfer surface (SRF1 ) matches the shape of the housing (CYLI ) of the motor MOTOR1 so as to effectively transfer heat via the heat transfer surface (SRF1 ).