GB2426805A

GB2426805A - Handheld tool which cannot be switched on if the safety brakes are not functional or are worn

Info

Publication number: GB2426805A
Application number: GB0610654A
Authority: GB
Inventors: Hanswerner Koegler; Egbert Steinbrueck; Juergen Dolata
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-06-01
Filing date: 2006-05-30
Publication date: 2006-12-06
Anticipated expiration: 2026-05-30
Also published as: FR2886564A1; DE102005024986A1; GB0610654D0; GB2426805B; FR2886564B1

Abstract

A handheld tool, in particular a motor chain saw comprises an operating element / trigger 10a with a switching on function for activating a drive / motor 12a, and a safety brake 14a, 16a for braking the drive depending on a cut-off condition, characterized in that the safety brake comprises means 18a for preventing the switching on function of the operating element 10a depending on the degree of wear / functional condition of at least one component 20a of the safety brake. The chains saw preferably has a touch sensitive element 26a supported on the brake band 20a of the safety brake, wherein the mechanical connection between the trigger 10a, and a switching mechanism 24a for closing an electrical circuit is interrupted when the brake band 20a breaks. A transmission element 22a ideally moves under spring bias to interrupt the physical connection. The cut-off condition could be the release of the trigger, or kickback.

Description

Machine tool

Prior art

The invention is based on a machine tool according to the preamble of claim 1.

From DE 196 18 640 Al a hand machine tool designed as a motor chain saw is known, comprising an operating element with a switching on function for activating a drive and with a safety brake for braking the drive depending on a cut-off condition. Cut-off conditions are letting go of the operating element by an operator and the occurrence of a return stroke of the motor chain saw, also designated as a kickback. In the first case a safety brake designed as a coasting brake acts and in the second case a safety brake designed as a kickback brake, which stops the drive and therefore the motor chain saw particularly quickly, acts.

Advantages of the invention The invention is based on a machine tool, in particular a hand machine tool, with an operating element with a switching on function for activating a drive and with a safety brake for braking the drive depending on a cut-off condition.

It is proposed that the safety brake comprises a means for preventing the switching on function of the operating element depending on a degree of wear of at least one component of the safety brake. In this way operation of the machine tool with worn safety-relevant parts can be prevented and a risk caused by functional failure of the safety brake can be safely avoided.

The means can be designed, for example, as an electronic, magnetic or mechanical means. The switching on function can be prevented by mechanical blocking or by disconnecting the drive from a power circuit or from some other kind of energy supply independent of the operating element. If the machine tool is equipped with an internal combustion engine, the means may also prevent ignition, for example.

If the machine tool comprises an electronic control unit, the means may, for example, also define a control bit, the value of which prevents the execution of the switching on function logically or by software.

In this context a "degree of wear" of the component is also intended to designate a discrete parameter for a state of the component, for example a number of linked components, so the means can also prevent the switching on function in the event of a broken and/or torn component.

The advantages of the solution according to the invention are brought home in particular in machine tools the operation of which with a worn safety brake is particularly fraught with danger and indeed in particular in hand machine tools and especially in chain saws with an electric motor, as here the safety brake must act particularly quickly on grounds of operating safety, also required by relevant standards. Examples of such relevant standards are DIN EN 50 14.4 - 2 - 13 or DIN EN 60745 - 2 - 13. A delay or a failure of a braking action of the safety brake because of wear, in particular in the case of kickback, in all probability leads to serious injury to the operator.

The switching on function of the operating element can be prevented structurally particularly simply and safely if the machine tool comprises a transmission element for producing and interrupting a mechanical connection between the operating element and a switching element for closing a power circuit. If the means is provided to influence a position of the transmission element the mechanical connection may be interrupted by displacing the transmission element and switching on or re-switching on the machine tool can be safely avoided.

Unintentionally putting the transmission elenent back into a position in which the mechanical connection between the operating element and a switching element is closed can be safely avoided if the means is provided to lock the transmission element in a position in which the mechanical connection between the operating element and a switching element is interrupted.

A machine tool according to the invention with a particularly fast-acting safety brake can be achieved if the component of the safety brake is designed as a brake strap.

LI

Particularly serious potential dangers can be prevented by the solution according to the invention if the safety brake is designed as a kickback brake of a chain saw or if the machine tool is designed as a chain saw. A chain saw of this kind advantageously comprises two safety brakes acting independently of one another, these being a coasting brake which brakes the drive if the operator lets go of the operating element and a kickback brake which brakes the drive very quickly if the motor chain saw kicks back in a direction of the operator.

Structurally simple detection or feeling of the degree of wear is achievable if the machine tool comprises a touch element supported on the component, the position of which then represents a parameter for the degree of wear. In principle, however, electronic, optical or other sensors appearing practical to the person skilled in the art for detecting the degree of wear can also advantageously be used.

Advantageous functional integration and reduction in the multiplicity of components are achievable if the safety brake is actuatable via the touch element or if a brake pressure or brake traction of the safety brake is generated by the touch element if at least one possible cut-off condition is present. The touch element can then be used both for detecting the degree of wear and for actuating the safety brake.

Drawings Further advantages emerge from the following description of drawings. In the drawings embodiment examples of the invention are illustrated. The drawings, the description and the claims contain numerous features in combination.

The person skilled in the art will also advantageously look at the features individually and put them together into practical further combinations.

Fig. 1 shows a motor chain saw in an overall view.

Fig. 2 shows the motor chain saw from Fig. 1 in a partial section with the drive cut off, the coasting brake switched on and the kickback brake switched off.

Fig. 3 shows the motor chain saw from Figs. 1 and 2 with the drive switched on, the coasting brake switched off and the kickback brake switched off.

Fig. 4 shows the motor chain saw from Figs. 1 to 3 with the kickback brake switched on.

Fig. 5 shows the motor chain saw from Figs. 1 to 4 with a worn or torn brake strap with the kickback brake switched on.

Fig. 6 shows an alternative motor chain saw in a partial section with the drive cut off, the coasting brake switched on and the kickback brake switched off.

Fig. 7 shows the motor chain saw from Fig. 6 with the drive switched on, the coasting brake switched off and the kickback brake switched off.

Fig. 8 shows the motor chain saw from Figs. 6 and 7 with the kickback brake switched on.

Fig. 9 shows the motor chain saw from Figs. 6 to 8 with a worn or torn brake strap with the kickback brake switched on.

Fig. 10 shows a transmission element and a means for preventing the switching on function of an operating element of the motor chain saw from Figs. 6 to 9 in a detailed view.

Fig. 11 shows a further alternative motor chain saw in a partial section with the drive cut off, the coasting brake switched on and the kickback brake switched off.

Fig. 12 shows the motor chain saw from Fig. 11 with the drive switched on, the coasting brake switched off and the kickback brake switched off.

Fig. 13 shows the motor chain saw from Figs. 11 and 12 with the kickback brake switched on.

Fig. 14 shows the motor chain saw from Figs. 11 to 13 with a worn brake strap and the drive switched off.

Description of the embodiment examples

Fig. 1 shows a machine tool, designed as an electric motor chain saw, in a perspective view. The motor chain saw comprises a guide rail 28a, known per se, with a chain 30a, a housing 32a with a rear handle 34a and with a front handle 36a, which is shielded in the direction of the guide rail 28a by a hand protector 38a. The rear handle 34a forms a closed, horizontal D shape, the upper, arch-shaped area of which is provided for placing a hand on, while the lower area protects the placed on hand. In the upper area of the rear handle 34a is arranged an operating element lOa, which has a switching on function for activating a drive 12a, arranged in a lateral housing part 40a and designed as an electric motor with a wattage of more than 1700. The drive 12a is activated if an operator closes a power circuit, comprising the drive 12a and running through a power supply cable 42a, by means of the operating element lOa in a way described further below. The housing 32a further has an orifice, closed by a lid 44a, for pouring in oil and a claw limit stop 46a.

Fig. 2 shows a partial section of the motor chain saw with a switching and braking device in a simplified illustration. The braking device comprises two safety brakes 14a, 16a, one safety brake 14a designed as a coasting brake, which stops the drive l2a and therefore the chain 30a within less than one second if the operator lets go of the operating element lOa, and a safety brake 16a designed as a kickback brake, which stops the drive 12a and the chain 30a within less than 0.15 seconds if, in the event of a kickback of the motor chain saw, the hand protector 38a is swivelled forwards relative to the housing 32a, i.e. in the direction of the guide rail 28a, because it is touched by a hand gripping the front handle 36a or by an arm of the operator.

Fig. 2 shows that the operating element lOa passes through a recess in the housing 32a and in the configuration without power illustrated in Fig. 2 is held in the recess by an actuating lever 48a. The actuating lever 48a is positioned in the housing 32a as swivellable about a swivel pin 50a and is loaded by a spring 52a of the safety brake 14a. The actuating lever 48a comprises a swivel arm 54a on the open end of which a traction element 56a acts, which is joined by a hinge to a swivel lever 58a, which is positioned on the housing 32a as swivellable about a swivel pin 60a and has a finger-shaped extension 26a which engages in a recess, not shown here, in a component of both safety brakes l4a, l6a, designed as a brake strap 20a. The extension 26a forms a touch element which is supported on the brake strap 20a when the safety brake 14a is closed.

The brake strap 20a is braced to the housing 32a at a first end via a clamping element 64a and is designed, e.g., as a 0.8 rnni thick band of steel sheeting. Other thicknesses, e.g. 1 rum are possible. The brake strap 20a is wrapped round a brake disc 66a, designed as a sintered component, from which in a power-free state it has a small radial distance and which it brakes very quickly if the brake strap 20a is stretched by one of the safety brakes l4a, l6a. The brake disc 66a is pressed on to a drive shaft 68a of the drive 12a, so the safety brakes l4a, 16a brake the drive 12a via the brake strap 20a.

In the configuration illustrated in Fig. 2 the extension 26a rests against an edge of the recess in the brake strap 20a, so part of the force generated by the spring 52a is supported on the brake strap 20a via the swivel arm 54a, the traction element 56a and the swivel lever 58a and stretches it round the brake disc 66a. This means that the safety brake 14a designed as a coasting brake is switched on and would brake the drive 12a if it were switched on.

If an operator actuates the operating element lOa, starting from the configuration illustrated in Fig. 2, by pushing it into the recess in the housing 32a against the spring force of the spring 52a, the actuating lever 48a resting against the inside of the operating element lOa swivels about the swivel pin 50a.

The actuating lever 48a has a slide support 70a, on which a transmission element 22a rests, which in the configuration illustrated in Fig. 2 is arranged between the actuating element 48a or the slide support 70a of the actuating lever 48a and a switching element 24a, mounted in the housing 32a arid designed as a push-button. The switching element 24a has a switch button 72a, spring-loaded from inside, which rests against the transmission element 22a. Owing to the swivelling movement of the actuating lever 48a the transmission element 22a bends round a contact element 74a which simultaneously stabilises a position of the transmission element 22a and pushes the switch button 72a into a housing of the switching element 24a. In this way, if the power supply cable 42a is connected to a power supply, the power circuit of the drive 12a is closed and the drive 12a is switched on. Therefore, in the configuration illustrated in Fig. 2 the operating element lOa has a switching on function.

Immediately before the power circuit is closed a traction transmitted on to the swivel lever 58a via the traction element 56a ceases. Because of this the extension 26a also no longer exerts tensile force on the brake strap 20a and the safety brake 16a is released, so the drive 12a can operate unbraked. At the end of the swivelling movement the configuration illustrated in Fig. 3, which is defined by a limit stop 90a of the operating element l0a, is reached.

If the operator lets go the operating element lOa, starting from the configuration illustrated in Fig. 3, a shut-off condition is met. The switching head 72a disengages, the power circuit and therefore the power supply of the drive 12a is interrupted and the drive l2a is braked by the safety brake 14a.

The transmission element 22a is positioned displaceably via a stud passing through an elongated hole 76a and also forming the swivel pin 60a, and via a second elongated hole 78a and is made of a very resilient, sturdy plastics material. In the area of the first elongated hole 76a the transmission element 22a has a means 18a like a leaf spring, extending in the direction of elongated hole 76a, which rests against a contact 92a moulded on to the housing 32a with slight bias and which is slightly bent round the contact 92a at its open end.

The hand protector 38a of the motor chain saw is swivellable about a swivel pin 80a and is connected via a stud 88a to a lever arm 82a of the second safety brake 16a, in which the second end of the brake strap 20a is suspended displaceably via an elongated hole. The hand protector 38a further has a stud 88a which engages in the second elongated hole 78a of the transmission element 22a. The stud 88a projects from the outside through the housing 32a, then through the lever arm 82a and through elongated hole 78a. When the hand protector 38a is swivelled the lever arm 82a is carried along by the stud 88a.

The position of the hand protector 38a illustrated in Figs. 2 and 3 is a first stable position of a bistable arrangement with a spring 84a which is stronger than spring 52a. If the operator pushes the hand protector 38a forwards against the force of spring 84a beyond a critical point in the direction of the guide rail 28a, a cut-off condition is met and the spring 84a acts on the lever arm 82a via an intermediate hinged part 86a. The lever arm 82a reverses until the brake strap 20a is stretched (knee lever principle). This activates the safety brake 16a designed as a kickback brake (Fig. 4) . Simultaneously the lever arm 82a pulls the transmission element 22a out of the intermediate space of the slide support 70a and the switch button 72a via the stud 88a, so the power circuit is interrupted arid the drive 12a cuts out automatically. This avoids the drive 12a operating against the safety brake 16a.

The means 18a then slides over the contact 92a until the contact comes to rest in the area of its open end. The exact point of contact depends here on an amplitude of the displacement movement of the transmission element 22a. This amplitude depends in particular on a thickness of the brake strap 20a and therefore on a degree of wear of the brake strap 20a and therefore represents a parameter for the degree of wear.

If the degree of wear is within a permissible scope, one side face of the means 18a always rests against the contact 92a and the operator can reactivate the machine tool by putting the hand protector 38a back into the position illustrated in Figs. 2 and 3. The transmission element 22a then slides back driven by a spring 94a tensioned between the transmission element 22a and the actuating lever 48a into the intermediate space of the slide support 70a and the switch button 72a, so the operating element lOa takes on the switching on function again.

The displacement of the transmission element 22a into the intermediate space of the slide support 70a and the switch button 72a and the pulling out of the transmission element 22a causes the transmission element 22a to produce a mechanical connection between the operating element lOa and the switching element 24a to close the power circuit or interrupts a connection of this kind.

If the degree of wear of the brake strap 20a has exceeded a critical value or if the brake strap 20a is broken or torn, the open end of the means 18a slides beyond the contact 92a and, owing to its bias, snaps outwards, so the spring 94a can no longer push the transmission element 22a automatically back into the intermediate space of the slide support 70a and the switch button 72a (Fig. 5) . The means 18a locks the transmission element 22a in the position illustrated in Fig. 5, in which the mechanical connection between the operating element lOa and the switching element 24a is interrupted. In this way the means 18a influences a position of the transmission element 22a. Automatic putting back of the transmission element 22a is possible only after the worn brake strap 20a has been replaced. In this way the operating element lOa is robbed of the switching on function. Actuation of the operating element lOa can no longer lead to switching on the drive 12a, so the means 18a prevents the switching on function of the operating element lOa.

Figs. 6 to 14 show further embodiment examples of the invention. In the description principally differences from the embodiment example illustrated in Figs. 1 to 5 are examined, reference being made to the description for the embodiment example illustrated in Figs. 1 to 5 as regards features which remain the same. Analogous features are provided with the same reference numerals, the letters a to d being added to distinguish the embodiment examples.

Figs. 6 to 10 show a second configuration of the invention with a means 18b for preventing a switching on function of an operating element lOb, designed as a locking projection moulded on to a transmission element 22b. A locking hook 98b positioned as swivellable about a swivel pin 50b is loaded in the direction of the means 18b by a torsion spring lOOb and is supported on this as long as a degree of wear of a component of two safety brakes 14b, 16b, designed as a brake strap 20b, is within a tolerance range (Figs. 6 to 8) . When the safety brake 16b, designed as a kickback brake, snaps in, the transmission element 22b moves relative to the locking hook 98b up to a point at which the brake strap 20b is stretched (Fig. 8) . The position of this point depends on the degree of wear of the component designed as a brake strap 20b. If the degree of wear is greater than a threshold value, the locking hook 98b hooks into a rear undercut 102b of the means 18b and locks the transmission element 22b in a position in which a mechanical connection between the operating element lOb and a switching element 24b is interrupted (Fig. 9) Fig. 10 shows the means 18b, part of the transmission element 22b and part of the actuating lever 48b in a perspective detailed view.

Figs. 11 to 14 show a motor chain saw in a third configuration of the invention with a means 96c, designed as a flat spiral spring element, for preventing a switching on function of an operating element lOc. The motor chain saw comprises a first safety brake l4c, designed as a coasting brake, and a second safety brake 16c, designed as a kickback brake.

The first safety brake 14c acts via an extension 26c of a swivel lever 58c on a component of the two safety brakes 14c, 16c, designed as a brake strap 20c, and passes through a recess in the brake strap 20c. A housing 32c of the motor chain saw has a guiding table 104c for guiding the brake strap 20c and a contact element 106c, arranged below the guiding table 1O4c. The means 96c is clamped in between the guiding table 104c and the contact element 106c and comprises a freely tensioned leg 62c which is deflected from an open end of the extension 26c in the direction of the contact element 106c if a degree of wear of the brake strap 20c is within tolerable limits.

If the first safety brake 14c, designed as a coasting brake, is closed, the extension 26c rests against a front edge of the recess in the brake strap 20c and stretches the brake strap 20c round a brake disc 66c, connected to a drive shaft 68c. A position of the recess in the brake strap 20c is defined by a degree of wear of the brake strap 20c. In this way the position of the extension 26c is also defined by the degree of wear.

If a degree of wear exceeds a critical value, on closing of the safety brake 14c, the extension 26c slides beyond an open end of the leg 62c of the means 96c and this snaps in behind the extension 26c, so the extension 26c can no longer swivel back. A carrier element 108c moulded on to the transmission element 22c and resting against the extension 26c carries the transmission element 22c with the extension 26c along with it, so in the event of considerable wear the transmission element 22c is also locked with the extension 26c in a position in which a mechanical connection between an operating element lOc and a switching element 24c of the motor chain saw is interrupted.

The extensjon 26c therefore forms a touch element for feeling the degree of wear of the brake strap 20c via which safety brake 14c is simultaneously actuatable in regular operation. The extension 26c or the touch element is supported on the component designed as a brake strap 20c when the safety brake 14c is closed.

Reference numerals operating element 12 drive 14 safety brake 16 safety brake 18 means brake strap 22 transmission element 24 switching element 26 extension 28 guide rail chain 32 housing 34 handle 36 handle 38 hand protector housing part 42 power supply cable 44 lid 46 claw limit stop 48 actuating lever swivel pin 52 spring 54 swivel arm 56 traction element 58 swivel lever swivel pin 62 leg 64 clamping element 66 brake disc 68 drive shaft slide support 72 switch button 74 contact element 76 elongated hole 78 elongated hole swivel pin 82 lever arm 84 spring 86 intermediate hinged part 88 stud limit stop 92 contact 94 spring 96 means 98 locking hook flat spiral spring 102 rear undercut

104 guiding table

106 contact element 108 carrier element

Claims

Claims 1. Machine tool, in particular hand machine tool, with an operating

element (lOa - lOc) with a switching on function for activating a drive (12a - 12c) and with a safety brake (14a - 14c, 16a - 16c) for braking the drive (12a - 12c) depending on a cut-off condition, characterised in that the safety brake (14a - 14c, l6a - 16c) comprises a means (18a, 18b, 96c) for preventing the switching on function of the operating element (l0a lOc) depending on a degree of wear of at least one component (20a - 20c) of the safety brake (14a - l4c, 16a - 16c)
2. Machine tool according to claim 1, characterised by a transmission element (22a - 22c) for producing and interrupting a mechanical connection between the operating element (lOa - lOc) and a switching element (24a - 24c) for closing a power circuit.
3. Machine tool according to claim 3, characterised in that the means (18a, l8b, 96c) is provided to influence a position of the transmission element (22a - 22c)
4. Machine tool according to claim 3, characterised in that the means (18a, 18b, 96c) is provided to lock the transmission element (22a - 22c) in a position in which the mechanical connection between the operating element (lOa - lOc) and a switching element (24a 24c) is interrupted.
5. Machine tool according to one of the preceding claims, characterised in that the component (20a - 20c) of the safety brake (14a - 14c, 16a - 16c) is designed as a brake strap.
6. Machine tool according to one of the preceding claims, characterised in that the safety brake (16a - 16c) is designed as a kickback brake of a chain saw.
7. Machine tool according to one of the preceding claims, characterised by a touch element (26a - 26c) supported on the component (20a - 20c)
8. Machine tool according to one of the preceding claims, characterised in that the safety brake (Ha - 14c) is actuatable via the touch element (26a - 26c)
9. A machine tool substantially as herein described with reference to the accompanying drawings.