DEAD MAN'S HANDLE FOR LAWN MOWERS

Abstract: The present invention relates to a dead man's handle device for a motor powered lawn mower (1), having an electrical device without moving parts to provide a dead man's handle function. A capacitive sensing device, preferably a coaxial cable (8), runs in the lawn mower handle (7). Said coaxial cable reacts when the handle (7) is touched and then allows motor activity, and the coaxial cable (8) provides stopping of the motor (5) when the contact is discontinued. The contact with the handle (performed e.g. by leaning the chest/body against the handle or placing the arm on the handle) may take place at an arbitrary location along the handle, making the dead man's handle function very comfortable in use. The lawn mower is also equipped with an alarm device (17) emitting alarm signals when the contact with the handle (7) is discontinued.

Description: TITLE OF INVENTION: DEAD MAN'S HANDLE FOR LAWN MOWERS Technical area The present invention relates to a motor powered lawn mower having an electrical device without moving parts to provide a dead man's handle function. This function will stop the motor driving the knives as soon as the user re- leases his grip on the handle, in order to avoid accidents. State of the art A variety of mechanical devices for providing a dead man's handle function are known, for petrol engine powered as well as electrically powered lawn mowers. Commonly, their function is such that when the user grips the handle, a lever or a button is depressed against the force of a return spring, allowing the motor to be kept running. As the user releases the handle, the lever or the button is returned to their respective original positions, stopping the motor. Electrical devices for providing a dead man's handle function are used within several different technical areas. The UK publication GB, A, 2 150 725 thus discloses a vehicle safety system. Capacitive sensors will sense a loose or a released hold on the steering wheel. Especially for car steering wheels, sensors which produce an alarm signal or stop the car if the steering wheel is released are fre¬ quently used. Commonly, these are optical sensors, but there are also steering wheels having embedded conductive strips, pressure or temperature sensitive detectors, etc. The French publication FR 2 383 268 discloses a roller, where a detector senses stray capacities from the user. In the European patent publication EP Al 0544483, a hand-held angle grinder is shown, one handle of which con- tains a metal strip. As the user grips the handle, the capacity of the metal strip is changed, which allows motor activity of the angle grinder,* if the user releases his grip on the handle the capacity of the metal strip is changed so as to increase the signal level, activating a comparator that switches off the motor. The German published patent application DE Al 2617460 discloses a.o. a lawn mower, the handle of which comprises two electrodes running parallel along the handle at a pre¬ determined distance from each other. As the user grips the handle, the electrodes are connected to each other, closing an electrical circuit which activates the motor of the lawn mower. When the user releases the handle, the electrical circuit is opened, stopping the motor. This dead man's handle function may also be equipped with a certain time delay, i.e. the motor is stopped when a predetermined time has passed after the handle was released. The various dead man's handle functions according to the documents described above show certain disadvantages. For example, the detecting device with the two electrodes used in the lawn mower described above is unpractical, as it implies that the user grips the handle and maintains a stationary grip as long as the mower is used; this in order to keep the electrical circuit closed. Furthermore, this detecting device is resistive, entailing low resistant de- sign and thus low sensitivity. The present invention eliminates the above disadvan¬ tages, as will be evident from the characterising part of patent claim 1. Further characteristics of the invention are described in more detail in the dependent patent claims. Summary of the invention The invention relates to a motor driven lawn mower having an electrical device without moving parts to provide a dead man's handle function, whereby a capacitive sensing device, preferably a coaxial cable, is running in the lawn mower handle, said coaxial cable reacting when the handle is touched and then allowing motor activity, and said coaxial cable providing stopping of the motor when the touch is discontinued. A detecting device allowing adequate setting of an appropriate capacitive sensitivity, detects the capacity of the coaxial cable in order to determine if the handle is touched or not. The coaxial cable of the sensing device functions as a capacitive sensor, and has the advantage, compared to re- sistive sensors, of needing no contact, i.e. very minor forces are needed to change the position of the sensor. As the sensing device can furthermore be adequately set to an appropriate sensitivity, only a very light grip around the handle or a light touch thereon is needed to keep the motor running. The grip around the handle or the touch of it (for example by leaning the chest/body against the handle or placing the arm on the handle) may take place at any loca¬ tion along the handle, making the dead man's handle function very comfortable in use. The invention will now be described in further detail below, with reference to the accompanying drawings. Brief description of the drawings Fig. 1 shows a motor powered lawn mower 1, comprising a motor housing 2, a control panel 3, an operating rod 4, a motor 5 and a relay 6, Fig. 2 shows the handle 7, comprising the cover 15 and the coaxial cable 8, Fig. 3 shows a frontal view of the control panel 3, Fig. 4 shows a cross section through the handle 7 of Fig. 2, along the line I-I, and Fig. 5 shows, schematically, the dead man's handle function of the lawn mower 1. Detailed description of an embodiment of the invention Fig. 1 shows a combustion fuel powered or electrically powered motor lawn mower 1 comprising a.o. a motor 5 driving the knives (not shown) and a relay 6, arranged in the motor housing 2, and an operating rod 4 and a control panel 3. The control panel, which includes a main switch 10, a start button 11, an alarm device 17, an adjustment knob 18 for the alarm device, a rotary variable capacitor 12 and control p.c. boards 14 for the electronic components, is arranged at the operating rod 4 in close vicinity of the lawn mower handle 7 (see Fig. 2) . The control p.c. boards 14 for the electronic components may as an alternative be located in the motor housing 2. An elastic cover 15, preferably made of a plastic resin material, closely envelops the handle section 16 of the operating rod. A coaxial cable 8 is embedded in the elastic cover 15 and runs along, and on the front (i.e. the side turned towards the user) side of, the handle section 16 so as to be easily touched by a hand or any other part of the body when the lawn mower is used (see Fig. 4) . In another embodiment, the coaxial cable 8 runs along the front side of the handle section underneath the elastic cover 15 an in yet another embodiment of the invention the coaxial cable is affixed to the exterior of the elastic cover 15 and runs along the front of the handle section 16. The coaxial cable 8 is further connected to a detecting device 13 inside the control panel. In the following text, handle 7 refers to the operating rod handle section 16 enveloped by said cover 15. The detecting device 13 is connected to the control p.c. boards 14, which, via electrical cables 9 inside the operating rod 4, operate the relay 6, said relay being connected to the motor 5. As the handle 7 is touched, preferably by applying the hand to it, the outer conductor of the coaxial cable is subjected to a small force, pressing it in towards the inner conductor. The touch of the handle 7 does not have to be made directly against the part containing the coaxial cable 8, but may be made against some other part of the handle, entailing that the cover 15 tightens around the coaxial cable, whereby the outer conductor of the coaxial cable is pressed in towards the inner conductor in the same way as above. When the distance between these two conductors, which are well insulated from one another, decreases, the capacitance of the coaxial cable increases. The detecting device 13 senses an increase DC in capacitance, whereby a corresponding voltage U 1 activates the control p.c. boards 14, allowing, by means of the relay 6, the motor 5 to run. When the contact is discontinued, preferably by removing the hand from the handle 7, the distance between the coaxial cable conductors will increase again, thus decreasing the capacitance of the coaxial cable. This decrease DC in capacitance is sensed by the detecting device 13, which generates a corresponding voltage U 2 that deactivates the control p.c. boards, causing the relay to switch off the motor. The sensitivity of the detecting device can be adjusted arbitrarily by varying the capacitance of the rotary vari¬ able capacitor 12; for example, when the capacitor 12 is turned to a position where it has a large capacitance, a strong grip around the handle 7 is required to keep the motor 5 running, whereas when the capacitor 12 is turned to a position where it has a small capacitance, a light touch of the handle is sufficient to keep the motor running. When using the lawn mower 1, the user shall set the main switch 10 to ON; next, the user may set the required sensitivity of the detecting device. In order to subse- quently start the lawn mower, the user grips the handle 7, preferably with one hand whilst at the same time pushing the start button 11, preferably with the other hand; thus, a dual control is required for starting the lawn mower. The user can now push the lawn mower forwards in front of him- self, using his hands or for example his chest/body if he wants to have his hands free. The user is not, as in the known art (e.g. the lawn mower according to DE Al 2617460) , required to grip the handle with his hands and maintain this static grip during the use of the lawn mower in order to keep the engine running,* such a procedure is very awkward and leads to the user quickly getting tired in both hands and arms. When the user releases his grip around the handle or when the contact with the handle by another body part (chest/body) is discontinued, the motor, and consequently the lawn mower, will stop immediately. After a predetermined time, preferably about 2 seconds after the contact with the handle 7 has ceased, the alarm device 17 is activated in order to indicate that the user should now switch off the lawn mower, i.e. set the main switch 10 to the OFF position. The alarm signals generated by the alarm device 17 may for example be sound signals or light signals. In a preferred embodiment of the present invention the alarm signals consist of beeping sound signals as well as of blinking light signals being emitted every other second with a reciprocal time interval of one second. The control panel 3 is furthermore equipped with an adjustment knob 18, by which a.o. the time delay from the discontinuation of contact with the handle 7 and activation of the alarm device 17 may be varied. Moreover, this adjust¬ ment knob may be used to adjust the levels of the sound and the light signals, as well as the reciprocal time interval between the sound and light signals respectively. Through the alarm signals, the user is thus reminded to switch off the lawn mower when it is no more to be used. This makes the lawn mower more childproof. If, however, the user is not finished using the lawn mower, he may start it by gripping the handle 7 in the same way as before with one hand and pushing the start button 11 with the other hand, whereupon the alarm signals will cease. This described embodiment of the present invention is to be regarded as an example only, and the invention is solely limited by the contents of the patent claims.

Claims: CLAIMS 1. Motor powered lawn mower (1) having an electrical device without moving parts to provide a dead man's handle function, characterized in that a capacitive sensing device (8) is provided in the lawn mower handle (7) , said sensing device responding when the handle (7) is touched and then allowing motor activity, whereby said sensing device pro¬ vides stopping of the engine (5) when the contact is dis¬ continued. 2. Motor powered lawn mower (1) according to claim l, characterized in that a detecting device (13) allows ade¬ quate setting of an appropriate capacitive sensitivity, and detects the capacity of the sensing device (8) in order to determine if the handle is touched or not. 3. Motor powered lawn mower (1) according to claim 2, characterized in that a rotary variable capacitor (12) is used to adjust the capacitive sensitivity of the detecting device (13) . 4. Motor powered lawn mower (1) according to claim 2, characterized in that when the handle is touched at an arbitrary location along the handle (7) , the capacitance of the sensing device (8) increases, whereby the detecting device (13) generates a voltage corresponding to this capacitance, activating the control p.c. boards (14) to allow power supply to the motor (5) , and when the contact is discontinued, the capacitance of the sensing device (8) decreases, whereby the detecting device (13) generates a voltage corresponding to the latter capacitance, deacti¬ vating said control p.c. boards (14) to shut off the motor (5) . 5. Motor powered lawn mower (l) according to any one of the preceding claims, characterized in that a control panel, (3) comprising a main switch (10) for the motor (5) , a start button (11) , a rotary variable capacitor (12) and control p.c. boards (14) for the electronic components, is provided at a suitable location along the operating rod (4) close to the handle (7) . 6. Motor powered lawn mower (1) according to claim 5, characterized in that said control p.c. boards (14) for the electronic components are arranged in the motor housing (2) . 7. Motor powered lawn mower (1) according to claim 5, characterized in that a dual command is required to start the motor (5) . 8. Motor powered lawn mower (1) according to claim 7, characterized in that the motor can only be started when the main switch (10) is in the ON position and the handle (7) is touched, preferably with one hand, at the same time as the start button (11) is depressed, preferably with the other hand. 9. Motor powered lawn mower (1) according to any one of the preceding claims, characterized in that an alarm device (17) is provided, emitting alarm signals when the contact with the handle (7) is discontinued. 10. Motor powered lawn mower (l) according to claim 9, characterized in that the alarm device is provided on the control panel (3) . 11. Motor powered lawn mower (1) according to any one of claims 9 or 10, characterized in that the alarm device (17) emits alarm signals when a predetermined time has passed after the contact with the handle (7) was discontinued. 12. Motor powered lawn mower (1) according to any one of claims 9 to 11, characterized in that said alarm signals are sound signals or light signals. 13. Motor powered lawn mower (1) according to claim 12, characterized in that said alarm signals consist of beeping sound signals as well as of blinking light signals, being emitted during different time intervals. 14. Motor powered lawn mower (1) according to any one of claims 9 to 13, characterized in that an adjustment knob (18) is provided on the control panel (3) , said knob being arranged for regulation of the time delay between the dis¬ continuation of the contact with the handle (7) and the activation of the alarm device. 15. Motor powered lawn mower (1) according to claim 14, characterized in that said adjustment knob (18) is further arranged for regulation of the levels of the sound and light signals respectively and of the reciprocal time interval between the emission of these signals. 16. Motor powered lawn mower (1) according to any one of the preceding claims, characterized in that the capacitive

Inventors: LINDEN TOMAS, LINDEN, TOMAS
Applicants: DAHLMANS KLIPPO AB
Application year: 1995
Main classification: F16P3
IPC codes: F16P3, H03K17