ANGLE MEASURING DEVICE

Abstract: Angle measuring device for vehicle-born chain saws, where a guide bar (18) for a saw chain is held by a rotatable holder (16), and the upper side of the holder is in sliding contact with the underside of a non-rotatable part (14) over a flat contact surface (21), the upper side of the holder provided with a multitude of recesses (22) along a circular arc, and the underside of the non-rotatable part provided with at least one magnetic head for registering the magnetic variations along the arc.

Description: ANGLE MEASURING DEVICE Background Vehicle-born chain saws for harvesting of trees comprise a felling head with a motor, usually hydraulic, and a guide bar with a saw chain. The guide bar is rotated around the drive shaft ofthe motor when the tree tTunk is to be sawn through, and it should also be radially movable to keep the chain tensioned with appropriate force. A chain saw drive device with these functions is described in patent application SE 95 00754-8. As is described in patent application SE 92 00610-5 and FI 95 0360 it is desirable to reduce the rotation angle ofthe guide bar to the least possible value, to save cutting time, and in case the sawing is combined with spraying ofthe sawn surface with iicquids such as fungicide or marking paint, to avoid spilling licquid outside the sawn surface. To achieve this, the angular motion must be measured, to ensure that the licquid spray starts and stops at the edges ofthe sawn surface, and that the return motion ofthe guide bar is started at the right time. SE 92 00610-5 shows how the angular position can be measured by a separate angular measuring device, connected to the guide bar through a geared connecting device. FI 95 0360 describes how the angle can be calculated by measuring the volume of hydraulic fluid pumped to the hydraulic positioning device. The present invention concerns an angular measuring device which is designed and located to be very insensitive to damage in spite ofthe difficult physical environment with sawdust, vibrations and impacts against the ground. Description An angular measuring device according to the invention is preferrably installed on a chain saw drive device such as described by SE 95 00754-8, as shown in figure 1. The drive device and the guide bar are located between an upper guard plate (1 1) and a lower guard plate (12), both being stationary parts ofthe felling head. A drive motor (13) is partially recessed through the upper guard plate (1 1) and attached to it by a flange (14). A bearing device (15) is attached to a cylindrical part ofthe motor exterior below the upper CONFIRMATION COPY guard plate and allows rotation of a bar holder (16) around the motor shaft. On the underside ofthe holder is a clamping device (17) to which the guide bar (18) is attached and which is radially displacable relative to the holder (16). The holder is rotated during sawing by a hydraulic cylinder (20) acting on a bolt ( 19) on the holder. The underside ofthe motor flange (14) and the upper side ofthe holder (16) are in sliding contact over a flat contact surface (21) which is robust and well protected from extemal damage. For transfer of licquids such as lubricating oil, fungicide or marking paint to the guide bar, this surface can be partially made as a swivel device with concentric grooves and seals. According to the invention, this contact surface (21 ) is also as shown in figure 2 made with a magnetically observable angular scale formed by a multitude of recesses (22) located along a circular arc. The recesses are preferrably made as round holes with equal distances. The angular scale is read by one or two magnetic heads recessed into the drive motor flange (14). Two reading heads at another distance than between the holes (22) allows determination ofthe rotational direction and a higher precision. If the contact surface (21) is used for a licquid swivel as well as an angular scale, the recesses (22) of the scale are preferably located radially outside ofthe swivel grooves, to get best resolution and precision.

Claims: Claims 1. Angle measuring device for vehicle-born chain saws, where a guide bar (18) is held by a rotatable holder (16), characterized by the upper side ofthe holder (16) being in sliding contact with the underside of a non-rotatable part (14) over a flat contact surface (21), and the upper side ofthe holder (16) being provided with a multitude of recesses (22) along a circular arc the center of which is the axis of rotation ofthe holder, and the underside ofthe non-rotatable part (14) being provided with at least one magnetic head for registering the magnetic variations caused by the recesses. 2. Angle measuring device according to claim 1, characterized by the contact surface (21) radially inwards from the circular arc being provided with concentric grooves and seals to form a swivel device for conveying licquids from the non-rotatable part (14) to the holder (16) and the guide bar (18). 3. Angle measuring device according to claim 1 or 2, characterized by the recesses (22) being made as round holes with uniform distances.

Inventors: LOEFGREN PER-OLAF, LOEFGREN, PER-OLAF
Applicants: LOEFGREN PER OLAF, SANDVIK AB, LOEFGREN, PER-OLAF, SANDVIK AKTIEBOLAG
Application year: 1997
Main classification: A01G23
IPC codes: A01G23