WO2012025458A1

WO2012025458A1 - Braking arrangement with controlled actuation for portable cutting tools and cutting tool therefor

Info

Publication number: WO2012025458A1
Application number: PCT/EP2011/064292
Authority: WO
Inventors: Paolo Cappellari; Luca Menghini
Original assignee: Redcap Technology S.R.L.
Priority date: 2010-08-24
Filing date: 2011-08-19
Publication date: 2012-03-01
Also published as: ITMI20101567A1; IT1401533B1

Abstract

A braking arrangement in a chainsaw or similar portable cutting tool is disclosed, comprising a braking device with a drum(5) and strap (6), acting on a cutting device (3)of said portable cutting tool, kept under load by first elastic means (10) the action of which is opposed by disengageable ratchet- gear means (7, 11, 11b, 11c, 12), said ratchet-gear means being disengageable by contact with a snap ratchet (13) arranged in close proximity thereto and integral in rotation with at least one safety lever (8) mounted pivoted(9) on the body (1) of a portable tool in the proximity of a grip (P) for the operator; said snap ratchet (13) is mounted pivoting(13a) on said safety lever (8) and is pushed towards said ratchet-gear means (11c) by second elastic means(14) in opposition to opposition means (15a) controlled by an electromechanical actuator (15), said electromechanical actuator being driven in the sense of displacing said opposition means (15a) to release the rotation of said ratchet (13), under the thrust of said second elastic means(14), at least upon the detection of a minimum distance between an operator and said cutting device (3) by a safety system apt to detect said minimum distance.

Description

BRAKING ARRANGEMENT WITH CONTROLLED ACTUATION FOR PORTABLE CUTTING TOOLS AND CUTTING TOOL THEREFOR

Field of the Invention

The present invention refers to a braking arrangement with controlled actuation for chainsaws and similar portable cutting tools .

Background Art

As is well known, there exists portable work equipment, such as chainsaws and the like, which comprises sharp moving parts and which exposes users to a high risk of injury. In fact, while it is relatively easy to arrange shields and/or accident- prevention safety elements on fixed equipment and machine tools, so as to avoid any accidental contact with moving parts, this is not equally feasible on portable equipment.

Safety arrangements, specifically dedicated to solving the safety problems connected with the use of such tools, have already been suggested for chainsaws and similar tools. In particular, two different approaches have been adopted, one based on a mechanical system and another one based on a remote detection system, both intended to stop the operation of the machine tools in case of accidental manoeuvres while handling the tool.

A particularly effective remote-type safety system is the one described in the application WO2007060698 and in the application filed at the same time in the name of the same Applicant. These safety systems generate a turn-off signal, apt to interrupt the power supply to the cutting tool, when a distance smaller than a threshold value is detected between the operator and the cutting blade.

In addition to these systems for the generic turning off of the tool, devices more specifically provided for braking have been suggested, i.e. suited to mechanically operate to immediately brake and stop the sharp moving part (typically the cutting chain in chainsaws), to limit the damages following a possible direct contact with the operator's body. As a matter of fact, in the absence of a stopping or braking device, the simple turning off of the tool would otherwise leave the cutting parts moving under the action of the inertia forces .

Moreover, safety technical regulations exist in the sector which provide the obligation to equip portable electrical saws and (combustion-engine-operated) chainsaws with a device capable of braking the rotation of the cutting part (traditionally a cutting chain slidably mounted on the edge of a support blade) when the tool undergoes a sudden and violent movement which might cause serious injury to the operator.

Typically, chainsaws are provided with strap-type braking or stopping systems, because they have proved effective and compact in this specific application.

In these devices a strap (usually a metal tape) is provided, which can be tightened circumferentially against a drum or other wheel integral with the rotation of the cutting chain, so as to brake by friction the rotation of said chain. The strap is actuated by a safety lever loaded by a snap spring. During standard operation, the strap is kept at a distance from the drum due to the presence of antagonist means which retain the safety lever in a home loaded position; as soon as the lever begins a pivoting movement, caused by the impact of the operator's hand gripping the tool, the antagonist means release the thrust of the spring: the lever is pushed to travel end with an elastic impulse which reflects in a swift rotation which drags one end of the strap and causes the braking action.

All these prior-art devices are of the passive type, i.e. they imply that the safety lever be passively stressed to rotation, to disengage from the antagonist means and thus cause the actuation of the spring and of the brake. Such way of intervening is not fully safe, because it is not guaranteed that in all hazard situations the operator is in such a condition as to impact against the safety lever; moreover, the portable tool may undergo sudden and violent movements, typically when there is discontinuity in the material being cut, which affect the operator' s balance - with potential hazardousness - without an impact by the hand on the safety lever necessarily taking place. This last case occurs in situations known as "kick-back" and gener- ates a situation of remarkable danger, despite not necessarily triggering the safety braking of the cutting chain.

In order to overcome these last conditions, snap systems have been proposed apt to intervene when a sudden movement of the tool occurs, even when the safety lever is not impacted by the hand, typically resorting to elements sensitive to inertia forces. In substance, an inertia sensor, such as an oscillating mass, is capable of performing a relative displacement when it undergoes an acceleration into a suitable direction (i.e. following a sudden movement of the tool towards the operator' s body) and thus triggers the intervention of the brake to cause the stopping of the cutting part. See, for example, DE3418059.

However, on a practical level, it has been detected that these inertia-based systems have an unreliable operation.

Summary of the Invention

The object of the present invention is hence to solve the disadvantages typical of prior-art braking arrangements, providing a braking arrangement and the relative cutting tool which, in addition to a passive-type mechanism, has an active actuation which is apt to operate when an objective hazardous situation arises (i.e. the operator's proximity to the sharp blade) regardless of which condition has arisen.

Such object is achieved by exploiting the turning-off signal of a safety system coexisting on the tool, for driving an actuation which acts on the kinematic chain of a braking arrangement of a passive, mechanical type.

In particular, such object is achieved through a braking arrangement as described in its essential features in the attached claims .

According to a main aspect of the invention, a braking arrangement for portable cutting tools is provided, of the type comprising a strap-type brake actuated by a spring-biased safety lever kept in a home and loaded position by disengageable retaining means, and equipped with trigger means for the disengagement of the retaining means which trigger means are actuated by briefly displacing the same safety lever, wherein the same disengagement trigger means are furthermore armed by a spring and kept in position against said spring by a pin actuated by an electromechanical actuator. Said actuator is actively driven by a signal issued by a proximity detection device, apt to determine when the relative distance between the operator and a cutting blade of the cutting tool drops to below a minimum threshold distance. Below such minimum distance, the proximity detection device issues a safety signal directed to the actuator, which causes the disengagement trigger means to move so as to release the safety lever loaded by the spring and hence trigger the actuation of the strap-type brake.

By another definition, according to an aspect of the invention, a braking arrangement is provided in a chainsaw or similar portable cutting tool, comprising a drum-and-strap braking device, acting on a cutting device of the portable tool, kept under load by first elastic means the action of which is opposed by disengageable ratchet-gear means, said ratchet-gear means being disengageable by contact with a snap ratchet arranged in close proximity thereto and integral in rotation with at least one safety lever mounted pivoting on the body of a portable tool in the proximity of a grip for the operator, wherein said snap ratchet is mounted oscillating on said safety lever and is pushed towards said ratchet-gear means by second elastic means in contrast with a rod movable by means of an electromechanical actuator, said electromechanical actuator being driven so as to move said rod for releasing the rotation of said ratchet, under the thrust of said second elastic means, at least upon detection of a minimum distance between one operator and said cutting device by a safety system apt to detect said minimum distance.

According to another aspect of the invention, the rod is kept projecting at its maximum extension, in conditions of standard operation, through the delivery of an excitation current towards said actuator, said pin being withdrawn following the lack of said excitating current. The actuator is fixedly mounted on said oscillating safety lever.

According to a preferred aspect, the ratchet-gear means comprise a rocker arm, mounted oscillating on a pivot integral with the body of the portable tool, having on one side a pawl suited to retain said safety lever against the thrust of said first elastic means and, on the other side, an actuation tail whereon said snap ratchet is apt to push.

According to another aspect, a portable cutting tool is provided equipped with a drive engine for moving a cutting device, furthermore comprising a drum-and-strap braking device acting on said cutting device, and a braking arrangement as detailed above.

Brief Description of the Drawings

Further features and advantages of the arrangement according to the invention will in any case be more evident from the following detailed description of a preferred embodiment of the same, given by way of example and illustrated in the attached drawings, wherein:

fig. 1 is a cross-section view of an embodiment of the present invention in a standard operation phase; and

fig. 2 is a cross-section view as shown in fig. 1 in a snapping phase of the safety device.

With reference to fig. 1, a chainsaw-shaped cutting tool is illustrated as an example. From a main chainsaw body 1 a cutting blade L extends overhanging, typically consisting of a support bar 2, on the peripheral edge of which a chain equipped with sharp edges 3 is slidably mounted. Within main body 1 the driving engine, the ignition system and the electric control circuits (not shown) are housed. The driving engine supplies driving force to a shaft laterally protruding from body 1 with a pinion 4 apt to drive into motion chain 3. On the same axis as pinion 4, a braking drum 5 is fastened whereon a braking strap 6 is wound, in a manner known per se.

The strap is fastened on one side (identified as F_x) to the frame of body 1 and on the other side to a pin 7 integral with a safety lever 8.

Said safety lever is in turn pivoted in rotation to the frame of body 1 on a rotation pin 9, preferably arranged in an advanced position (i.e. towards the right in the drawing) with respect to grip P whereon an operator acts to handle the chain- saw .

Lever 8 - and consequently the end of the strap 6 fastened to pin 7 - is pushed in the clockwise rotation direction (arrow R) by elastic means 10, such as a helical spring, kept loaded between lever 8 and the frame of body 1 by the arranging of a rocker arm 11.

Rocker arm 11 defines an abutting shelf 11a for spring 10 and, at the same time, keeps lever 8 fastened to itself, so as to keep spring 10 loaded. In particular, rocker arm 11 is mounted pivoting on a central pin 12, fastened to the body 1 of the chainsaw, and has a pawl lib apt to engage with the pin 7 of lever 8. The rocker arm can hence oscillate about central pin 12 between an engagement position, wherein it retains pin 7 and hence keeping spring 10 loaded, and a disengagement position (shown in fig. 2), wherein it disengages pin 7 and hence releases the clockwise rotation of lever 8 under the elastic thrust of spring 10. The clockwise rotation of lever 8 causes a displacement of pin 7 about the rotation axis arranged in pin 9 and hence determines a traction on braking strap 6.

Rocker arm 11 is furthermore equipped with a tail 11c which ends in the close proximity of a snap ratchet 13 mounted integral with lever 8. In a manner known per se, when the operator's hand suddenly moves closer to safety lever 8, pressure is applied on the lever which - exploiting the plays existing in the mechanism - tends to displace by a small extent snap ratchet 13, pushing it onto the tail 11c of the rocker arm. The pressure on tail 11c tends to cause rocker arm 11 to rotate about central pin 12 and hence to disengage pawl lib from pin 7: the action of spring 10 is therefore triggered, as well as the sudden braking action of strap 6 on drum 5.

Snap ratchet 13 pivots about an own rotation pin 13a, integral with lever 8, and is kept pushed towards the tail 11c of rocker arm 11 by elastic means 14, for example acting between ratchet 13 and lever 8. In operating conditions, ratchet 13 is kept detached from tail 11c by controllable opposition means 15 which act in opposition to spring 14, as clearly shown in fig. 1.

According to the invention, piloting opposition means 15 are shaped as an actuator provided with a small control rod 15a, which may be extracted or withdrawn based on an electric control signal. The actuator is fastened to lever 8 and determines the movement of control rod 15a with respect to ratchet 13.

Advantageously, actuator 15 is of an electromechanical type and, in standard operating conditions, i.e. with rod 15a fully extracted, is preferably kept excited by a electric supply source comprised within the body of chainsaw 1. Such solution automatically ensures that, in the absence of electric supply (typically before engine start) the safety system cannot be kept automatically armed, but must be manually and voluntarily kept in such position (fig. 1), thereby increasing the level of passive safety.

Actuator 15 is driven based on a safety signal deriving from a proximity detection system, i.e. a safety system apt to define when the operator reaches a minimum threshold distance from the blade L of the tool. A particularly effective safety system for piloting actuator 15 is like the one defined in the contemporary application filed by the same Applicant.

In substance, when blade L moves closer to the operator by a distance below a safety threshold - for example due to an abrupt movement, such as a so-called "kick-back", which does not necessarily cause the operator' s impact against lever 8 - the safety system issues a disengagement signal which drives actuator 15 and possibly, at the same time, cuts off the supply to the tool motorisation . Upon a control, or simply following supply cut-off, the actuator withdraws control rod 15a, disengaging snap ratchet 13 which, under the impulse of elastic means 14, pushes on tail 11c determining the action of strap 6 in the way indicated above.

A similar braking action, through the tensioning of strap 6, can be actively achieved also in other predetermined condi- tions. For example, it can be provided that when the operator releases the grip or moves away from the tool - which is detected by the integrated capacitive safety system - an "inactivity" signal is issued which provides to drive actuator 15 in the same way indicated above, i.e. releasing ratchet 13. This ensures that cutting chain 3 be kept braked even when the chainsaw may be substantially abandoned with a running engine.

After intervention of actuator 15 and the braking action of strap 6, the rearming of the safety device is performed by simply manually rotating lever 8 in an anti-clockwise direction, after having brought actuator 15 back into its operational state (i.e. with the rod extracted) . This causes the fastening of pawl lib to pin 7 and the engagement of ratchet 13 - pushed into rotation by tail 11c - with rod 15a. For such purpose, it is preferable that at least the terminal portion of rod 15a be axially slidable and elastically pushed outwards: this allows to bring the ratchet back into the armed position of fig. 1 simply overcoming mechanically the elastic thrust of rod 15a, without having to act on actuator 15 to achieve a withdrawal/drawing out synchronised with the rearming phase.

Due to the design of the invention it is possible to supply a simple and effective safety system, suited to operate both passively - following the operator' s impact against safety lever 8 - and actively, through the electric signal determined by a proximity safety device. The system of the invention no longer requires the presence of an inertia system, in any case of the passive principle, which used to complicate and made prior-art safety systems unreliable.

Finally, the active operation system suggested by the invention is well-suited to be used also outside classic danger conditions, for example, as indicated above, whenever the tool is simply abandoned by the operator with the engine on.

However, it is understood that the invention is not limited to the particular arrangement illustrated above, which represents only a non—limiting example of the scope of the invention, but that a number of variants are possible, all within the reach of a person skilled in the field, without necessarily departing from the scope of the invention.

For example, although in the description reference has been made to a specific braking system of a chainsaw, it is understood that the same principle configuration may be applied also to other systems mounted on other portable cutting equipment .

Claims

1. Braking arrangement in a portable cutting tool, comprising a braking device, acting on a cutting device (3) of said portable cutting tool, kept under load by first elastic means (10) the action of which is opposed by disengageable ratchet-gear means (7, 11, lib, 11c, 12), said ratchet-gear means being disengageable by contact with a snap ratchet (13) arranged in close proximity thereto and integral in rotation with at least one safety lever (8) mounted pivoted (9) on the body (1) of a portable tool in the proximity of a grip (P) for the operator, characterised in that said snap ratchet (13) is mounted pivoting (13a) on said safety lever (8) and is pushed towards said ratchet-gear means (11c) by second elastic means

(14) in opposition to opposition means (15a) controlled by an electromechanical actuator (15), said electromechanical actuator being driven in the sense of displacing said opposition means

(15a) to release the rotation of said ratchet (13), under the thrust of said second elastic means (14), at least upon the detection of a minimum distance between an operator and said cutting device (3) by a safety system apt to detect said minimum distance .

2. Braking arrangement as claimed in claim 1, wherein said opposition means are shaped as a movable rod (15a) .

3. Braking arrangement as claimed in claim 2, wherein said rod (15a) is kept projecting at the maximum extension thereof, in standard operating conditions, through the delivery of an excitation current towards said actuator (15), said rod (15a) being withdrawn following the lack of said excitation current.

4. Braking arrangement as claimed in claim 1, 2 or 3, wherein said actuator (15) is fixedly mounted on said pivoting safety lever (8) .

5. Braking arrangement as claimed in any one of the preceding claims, wherein said ratchet-gear means comprise a rocker arm (11), mounted pivoting on a pin (12) integral with the body of the portable tool, having on one side a pawl (lib) suited to retain said safety lever (8) against said first elastic means (10) and, on the other side, an actuation tail (11c) whereon said snap ratchet is apt to push (13) .

6. Portable cutting tool equipped with a driving engine for moving a cutting device (3), furthermore comprising a braking device with drum (5) and strap (6) acting on said cutting device (3), characterised in that it comprises a braking arrangement as claimed in any one of the preceding claims .

7. Braking arrangement in a portable cutting tool, comprising a strap-type braking device actuated by a spring- biased safety lever kept in a home and loaded position by disengageable retaining means, and equipped with trigger means for the disengagement of said retaining means, which trigger means are actuated by displacement of said safety lever, characterized in that said trigger means are furthermore armed by a spring and kept in position against said spring by a pin actuated by an electromechanical actuator driven by a proximity detection device, apt to issue a safety signal to the actuator, which causes the disengagement trigger means to disengage said retaining means so as to release said safety lever loaded by the spring and hence trigger the actuation of the strap-type braking device, when the relative distance between an operator and a cutting blade of the cutting tool drops to below a minimum threshold distance.