Patent ID: 8818548

Claim:
A work apparatus including a cutting tool and equipped with a safety device for stopping motion of the cutting tool upon detection of a particular phenomenon possibly inviting an unexpected, unsafe situation from acceleration information received from an acceleration sensor, comprising: a single-cylinder internal combustion engine mounted in a drive unit in which a drive source for driving said cutting tool is provided; a uniaxial, biaxial, or triaxial type acceleration sensor having one, two, or three detection axes and attached to said drive unit in such an orientation that said detection axes of said acceleration sensor extend aslant from an axial line of a cylinder bore of said internal combustion engine; an arithmetic operation means supplied with acceleration information from said acceleration sensor and executing arithmetic operation of the acceleration information to find out an acceleration peak; a frequency range judgment means for judging whether or not the acceleration peak found out by said arithmetic operation means is within a first frequency range in which acceleration peaks indicative of phenomena possibly inviting any unexpected, unsafe situations normally appear; an amplification means for amplifying the acceleration peak in the first frequency range when the frequency range judgment means determines that the frequency of the acceleration peak is in the first frequency range; a first comparison means for comparing the acceleration peak amplified by the amplification means with a first threshold; a second comparison means for comparing the acceleration peak with a second threshold when the frequency range judgment means determines that the frequency of the acceleration peak is in a frequency out of the first frequency range; and an output means for issuing a safety signal to a disabling means when comparison of said first comparison means results in determining that the acceleration peak in the first frequency range is equal to or higher than the first threshold or when comparison of said second comparison means results in determining that the acceleration peak in the acceleration peak in the frequency range out of the first frequency range is equal to or higher than the second threshold, said disabling means responsively disabling said cutting tool of said work apparatus directly or indirectly to stop the cutting tool from moving.