GB2477037A

GB2477037A - Electric motor no-load speed reduction for power saving

Info

Publication number: GB2477037A
Application number: GB1100867A
Authority: GB
Inventors: Csaba Liptak; Csaba Levai
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-01-19
Filing date: 2011-01-18
Publication date: 2011-07-20
Anticipated expiration: 2031-01-18
Also published as: GB2477037B; GB201100867D0; DE102010001030B4; DE102010001030A1; CN102152283B; CN102152283A; RU2011101641A

Abstract

In a cordless hand tool 100 having a drive motor 180 for driving a tool 120, the drive motor 180 is configured to drive the tool 120 at a preset operating speed in the load mode and in the no-load mode and a control unit 170 is provided, configured to reduce the preset operating speed in the no-load mode to a preset at-rest speed. The motor speed is increased to the operating speed from the at-rest speed if the tool 100 changes from the no-load mode to the load mode, e.g. as a portable sanding machine is applied to a workpiece. There may be a preset delay after the tool 100 enters the no-load state before the motor speed is reduced to the at-rest speed, the delay may be between 0.5 and 2.5 seconds. The motor current may be monitored to establish whether the tool 100 is operating in the no-load mode or the load mode. The at-rest speed may be less than 20% to 40% of the operating speed. The operating speed may be a working speed in the load mode or an idling speed in the no-load mode, the idling speed being higher than the at-rest speed. Reducing the no-load motor speed saves power and avoids rapidly discharging a battery pack 190.

Description

Description Title

Cordless hand tool machine and method of operating a cordless hand tool machine

Background art

The present invention relates to a cordless hand tool machine having a drive motor for driving a tool, wherein the drive motor is configured to drive the tool after switching-on of the cordless hand tool machine at a preset operating speed in the load mode and in the no-load mode.

From the background art such cordless hand tool machines are known, in which an on/off switch is provided for switching the machine on and off. In the switched-on state of the tool machine an associated drive motor is operated at a substantially constant operating speed, independently of whether the hand tool machine is working in the no-load mode or in the load mode.

The cordless hand tool machine may moreover comprise a speed controller. This enables a user to adjust the operating speed in the load mode to a suitable working speed and in the no-load mode to an idling speed that is reduced compared to the working speed.

The drawback of the background art is that, given operation of the cordless hand tool machine at a substantially constant operating speed that is independent of the operating state, a comparatively large amount of motor current is to be provided by the associated battery pack, thereby leading to an undesirably rapid discharge of the battery pack and hence a limiting of the operating duration of the tool machine. Even in the case of operation of the cordless hand tool machine with the reduced no-load voltage, as a rule a comparatively large amount of motor current is still provided by the associated battery pack, thereby leading in turn to an undesirably rapid discharge of the battery pack and hence a limiting of the operating duration of the tool machine.

Disclosure of the invention

A problem of the invention is therefore to provide a new cordless hand tool machine that has a reduced current consumption.

This problem is solved by a cordless hand tool machine having a drive motor for driving a tool. The drive motor is configured to drive the tool after switching-on of the cordless hand tool machine at a preset operating speed in the load mode and in the no-load mode. A control unit is provided, which is configured to reduce the preset operating speed in the no-load mode to a preset at-rest speed.

The invention therefore enables the provision of a cordless hand tool machine, in which through use of a low-cost control unit a reliable reduction of the current consumption in the no-load mode and hence an effective prolongation of the operating duration may be achieved.

The control unit is preferably configured to measure a motor current supplied to the drive motor and to determine as a function of the measured motor current whether the cordless hand tool machine is being operated in the no-load mode or in the load mode.

Thus, an instantaneous operating state of the cordless hand tool machine may be determined in each case in a simple manner.

According to a form of implementation the control unit is configured to reduce the preset operating speed to the preset at-rest speed at the earliest after a preset time period in the no-load mode of the cordless hand tool machine has elapsed.

In this way an unwanted and disturbing reduction of the operating speed may be avoided.

The preset time period is preferably preselectable from a time of 0.5s to 2.5s.

In this way a reduction of the operating speed may be rapidly and easily achieved.

The problem described initially is also solved by a method of operating a cordless hand tool machine having a drive motor for driving a tool, which after switching-on of the cordless hand tool machine is driven at a preset operating speed of the drive motor in the load mode and in the no-load mode. The preset operating speed is reduced in the no-load mode to a preset at-rest speed.

The invention therefore easily enables a reduction of the current consumption of the cordless hand tool machine in the no-load mode and hence an effective prolongation of the operating duration thereof.

The preset at-rest speed is preferably increased to the preset operating speed if the cordless hand tool machine changes from the no-load mode to the load mode.

Safe and reliable operation of the cordless hand tool machine may therefore be achieved.

According to a form of implementation the preset operating speed is reduced to the preset at-rest speed at the earliest after a preset time period in the no-load mode of the cordless hand tool machine has elapsed.

An unwanted and disturbing reduction of the operating speed may therefore be avoided.

The preset time period is preferably at least 0.5s and/or not more than 2.5s.

A rapid and reliable reduction of the operating speed may therefore be achieved.

According to a form of implementation a motor current supplied to the drive motor is measured. As a function of the measured motor current it is determined whether the cordless hand tool machine is being operated in the no-load mode or in the load mode.

The invention therefore enables easy and reliable determination of an instantaneous operating state of the cordless hand tool machine.

The preset at-rest speed is preferably not more than 20% to 40% of the preset operating speed.

A comparatively large reduction of the operating speed in the no-load mode may therefore be achieved.

According to a form of implementation the preset operating speed is realized in the load mode by a working speed and in the no-load mode by an idling speed, wherein the working speed is higher than the idling speed. The preset at-rest speed is preferably lower than the idling speed.

Thus, a reduction of the operating speed may be used in a simple manner in cordless hand tool machines, in which an associated idling speed in the no-load mode is already

adjustable.

Brief description of the drawings

There now follows a detailed description of embodiments of the invention, which are represented in the drawings. The drawings show: Fig. 1 a diagrammatic view of a cordless hand tool machine according to a form of implementation, Fig. 2 a measurement diagram of a motor current and an associated operating speed during operation of the cordless hand tool machine of Fig. 1, and Fig. 3 a flowchart of a method of operating the cordless hand tool machine of Fig. 1 according to a form of implementation.

Description of the embodiments

Fig. 1 shows by way of example a cordless hand tool machine 100, which has a housing 105. According to a form of implementation the cordless hand tool machine 100 is connectable for mains-independent power supply mechanically and electrically to a battery pack 190. This, as illustrated, is disposed and fastened in the housing 105 but may alternatively take the form of a replacement battery pack that may be fastened mechanically to the housing 105 or be at least partially inserted therein.

In the housing 105 an electric drive motor 180, which is supplied with power from the battery pack 190, and an associated control unit 170 are disposed. The drive motor is actuable, i.e. may be switched on and off, by means of a manual switch configured for example as an on/off switch and may be any desired type of motor, for example an electronically commutated motor or a d.c. motor. As the operating mode and construction of a suitable drive motor are sufficiently known from the background art, for the sake of conciseness of the description these are not described in detail here.

The drive motor 180 is configured, after the cordless hand tool machine 100 has been switched on by means of the on/off switch 195, to drive a tool 120 associated with the cordless hand tool machine 100 at a preset operating speed both in the load mode and in the no-load mode. The drive motor 180 may further comprise a speed controller, which for example enables a user to adjust the operating speed in the load mode to a suitable working speed, while the cordless hand tool machine 100 in the no-load mode is operated at an idling speed that is reduced compared to the operating speed and preset by the speed controller.

According to a form of implementation the control unit 170 is configured to detect the no-load mode and/or a change from the load mode to the no-load mode of the cordless hand tool machine 100 and in the no-load mode to reduce the preset operating-or idling speed to a preset at-rest speed. The preset at-rest speed is therefore lower than the preset operating speed and/or lower than the preset idling speed and is preferably not more than 20% to 40% of the preset operating-and/or idling speed. In this case, the control unit 170 reduces the preset operating speed to the preset at-rest speed at the earliest after a preset time period in the no-load mode has elapsed, which is preferably not less than 0.5s and not more than 2.5s. The control unit 170 is further configured to detect the load mode and/or a change from the no-load mode to the load mode and in the load mode to increase the preset at-rest speed to the preset operating speed.

To enable detection of the no-load mode and/or the load mode, the control unit 170 is configured for example to measure a motor current I supplied to the drive motor 180 by the battery pack 190 and as a furction of the measured motor current I to determine whether the cordless hand tool machine 100 is being operated in the no-load mode or in the load mode. For this purpose, the control unit 170 may comprise suitable, digital electronic components, which, since they are known to the person skilled in the art, for

the sake of conciseness of the description are not

described in detail here. The operating mode of the control unit 170 is described by way of example in Figs. 2 and 3.

In Fig. 1 the cordless hand tool machine 100 is configured by way of example as a cordless sanding machine. This has a sanding plate 122, which is disposed on the housing 105 and on the underside of which a sanding block 124 formed for example from cellular rubber and covered by an abrasive paper 126 is provided. The sanding plate 122, the sanding block 124 and the abrasive paper 126 form for example the tool 120. As illustrated, the housing 105 is limited in its extent approximately to an area 132 of the sanding plate 122. Disposed above an area 142 of the housing 105 are substantially all of the components of the sanding machine 100 that are situated inside the housing 105, such as for example the control unit 170, the drive motor 180 and the battery pack 190.

It is however pointed out that the present invention is not limited to cordless sanding machines, rather it may be applied to different, in particular battery-operated electric tools, in which a drive motor during operation of the machine is operated at a substantially constant operating speed and/or at a suitable working speed or a preset idling speed, for example to a cordless polishing device, a cordless cutting device etc. Furthermore, the invention may be applied also to electric tools that are provided for mains operation.

Fig. 2 shows a measurement diagram 200 of a motor current 210 supplied to the drive motor 180 of Fig. 1, as well as a correlated measurement diagram 250 of a motor speed 260 produced in each case by this motor current 210 during an exemplary operation of the cordless hand tool machine 100 of Fig. 1. The diagram 200 has an ordinate 202 representing a respective absolute value of the motor current 210 as well as an abscissa 204 representing time.

The diagram 250 has an ordinate 252 representing a respective absolute value of the motor speed 260 as well as an abscissa 254 representing time.

In the measurement diagram 200 the cordless hand tool machine 100 is initially in the load mode, so that a first motor current 220 flows in the drive motor 180, until at the time 222 the load mode is terminated, for example by removal of the cordless hand tool machine 100 from an associated work surface. The motor current 210 therefore decreases and from a time 224 falls below a preset upper threshold value 212, with the result that the no-load mode is detected. At the time 227 the motor current 210 then has for example a preset nominal value 214, which in the no-load mode is sufficient to maintain a preset operating speed 262. The drive motor 180 is then, as illustrated, energized up to the time 226 with the motor current 210 having the preset nominal value 214. Thus, the drive motor up to the time 226 rotates independently of its operating state at the preset operating speed 262.

At the time 226 a time period 225 since the time 224, at which the motor current 210 fell below the preset upper threshold value 212, has elapsed, which corresponds to a preset minimum time period Tmin, after the elapsing of which the motor speed 260 and/or the preset operating speed 262 in the no-load mode is reduced to a preset at-rest speed 264, for example by lowering the motor current 210 to a preset quiescent value 218, at which the drive motor 180, as illustrated, is energized from the time 228.

At the time 232 a load is applied anew to the drive motor 180, for example by placing the cordless hand tool machine once more onto an associated work surface, with the result that the motor current 210, as shown in the measurement diagram 200, increases until it exceeds a lower threshold value 216 at the time 234, with the result that a renewed load mode is detected. The motor speed 260 is therefore increased from the at-rest speed 264 back up to the operating speed 262, with the result that the motor current 210 increases to a current value 230 and the drive motor 180 from the time 236 is driven once more at the operating speed 262.

At the time 242, as illustrated, the renewed load mode is then terminated, with the result that the motor current 210 decreases again and from a time 244 falls below the preset upper threshold value 212, with the result that the no-load mode is detected once more. The drive motor 180 is then energized with the motor current 210 having the preset nominal value 214 up to the time 246, at which a time period 245 has elapsed since the time 244. This time period 245 is for example shorter than the preset minimum time period Tmin, with the result that the motor speed 260 and/or the preset operating speed 262 is not reduced to the preset at-rest speed 264. At the time 246 a load is applied anew to the drive motor 180, with the result that the motor current 210, as shown in the measurement diagram 200, rises to a current value 270 and once more exceeds the upper threshold value 216, with the result that the no-load mode is no longer detected.

At the time 272 the load mode is then terminated once more, with the result that the motor current 210 decreases anew and from a time 274 falls below the preset upper threshold value 212, with the result that the no-load mode is detected anew. The drive motor 180 is then energized with the motor current 210 having the preset nominal value 214 up to the time 276, at which since the time 274 a time period 275 that for example likewise corresponds to the preset minimum time period Tmin has elapsed, with the result that the motor speed 260 and/or the preset operating speed 262 is reduced once more to the preset at-rest speed 264, at which the drive motor 180, as illustrated, is driven anew from the time 278. Up to the time 276 the drive motor 180 however independently of its operating state rotates at the preset operating speed 262, as is evident from the diagram 250.

Fig. 3 shows by way of example a method 300 of operating the cordless hand tool machine 100 of Fig. 1. According to a form of implementation this method 300 is executed by the control unit 170 of Fig. 1, which, as described in Fig. 1, controls the drive motor 180 of Fig. 1. The method 300 starts in step S310 with switching-on of the cordless hand tool machine 100 by means of the manual switch 195 of Fig. 1.

In step S320 the drive motor 180 is driven at a preset operating speed (for example the operating speed 262 of Fig. 2) . In step S330 it is determined whether the cordless hand tool machine 100 is being operated in the no-load mode or in the load mode. For this purpose, according to a form of implementation as described above for Fig. 2 a motor current supplied to the drive motor 180 is measured in order on the basis of the measured motor current to determine the respective operating state. If in step S330 the load mode is detected, the method returns to step S320.

If in step S330 the no-load mode is detected, the method 300 continues in step S340, where a time period is measured, which indicates how long the cordless hand tool machine 100 is operated in the no-load mode. In step S350 it is then determined whether the measured time period is greater than or equal to a preset minimum time period (for example Tmin in Fig. 2) . If so, the method 300 continues in step S360. Otherwise the method 300 returns to step S340.

In step 360 the preset operating speed is reduced to a preset at-rest speed (for example the at-rest speed 264 of Fig. 2) . In step S370 it is then determined whether the cordless hand tool machine 100 is still being operated in the no-load mode. If so, the method 300 returns to step S360. Otherwise the method 300 returns to step S320.

Claims

Claims 1. Method of operating a cordless hand tool machine (100) having a drive motor (180) for driving a tool (120), which after switching-on of the cordless hand tool machine (100) is driven in the load mode and in the no-load mode at a preset operating speed of the drive motor (180), characterized in that the preset operating speed is reduced in the no-load mode to a preset at-rest speed.
2. Method according to claim 1, characterized in that the preset at-rest speed is increased to the preset operating speed if the cordless hand tool machine (100) changes from the no-load mode to the load mode.
3. Method according to claim 1 or 2, characterized in that the preset operating speed is reduced to the preset at-rest speed at the earliest after a preset time period in the no-load mode of the cordless hand tool machine (100) has elapsed.
4. Method according to claim 3, characterized in that the preset time period is at least 0.5s.
5. Method according to claim 3 or 4, characterized in that the preset time period is not more than 2.5s.
6. Method according to one of the preceding claims, characterized in that a motor current (I) supplied to the drive motor (180) is measured and as a function of the measured motor current it is determined whether the cordless hand tool machine (100) is being operated in the no-load mode or in the load mode.
7. Method according to one of the preceding claims, characterized in that the preset at-rest speed is not more than 20% to 40% of the preset operating speed.
8. Method according to one of the preceding claims, characterized in that the preset operating speed is realized in the load mode by a working speed and in the no-load mode by an idling speed, wherein the working speed is higher than the idling speed, characterized in that the preset at-rest speed is lower than the idling speed.
9. Cordless hand tool machine (100) having a drive motor (180) for driving a tool (120), wherein the drive motor (180) is configured to drive the tool (120) after switching-on of the cordless hand tool machine (100) at a preset operating speed in the load mode and in the no-load mode, characterized in that a control unit (170) is provided, which is configured to reduce the preset operating speed in the no-load mode to a preset at-rest speed.
10. Cordless hand tool machine (100) according to claim 9, characterized in that the control unit (170) is configured to measure a motor current (I) supplied to the drive motor (180) and as a function of the measured motor current to determine whether the cordless hand tool machine (100) is being operated in the no-load mode or in the load mode.
11. Cordless hand tool machine (100) according to claim 9 or l0,.characterjzed in that the control unit (170) is configured to reduce the preset operating speed to the preset at-rest speed at the earliest after a preset time period in the no-load mode of the cordless hand tool machine (100) has elapsed.
12. Cordless hand tool machine (100) according to claim 11, characterized in that the preset time period is preselectable from a time of 0.5s to 2.5s.
13. A method substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
14. A cordless hand tool machine as hereinbefore described with reference to and as shown in the accompanying drawings.