Laser reference device

Claim 1

In combination, a beam sender 45 including a laser beam source 53 for radiating a laser beam and a scanner 67 for scanning the laser beam radiated from said laser beam source, said scanner 67 including a mirror holder 75 and mirrors 77, 79 held on opposite surfaces of said mirror holder rotatably supported in the path of the laser beam by a pair of space bearings 71, 73 and rotatable about an axis 69 with said bearings being spaced apart from each other as far as possible for reducing the deflection of the radiated laser beam from a plane normal to said axis due to the play in the bearing, a working lorry, a screed 7 towed by said working lorry, a pair of screed adjusting arms 11, 11' each connected at one of their ends to said screed, said working lorry including means 19, 19' for raising and lowering the other ends of said adjusting arms to increase or decrease the incline of said screed, a cross beam 25 mounted on and extending across said adjusting arms, a beam receiver 47 mounted at one end of said cross beams to detect the height of the screed above or below the radiated laser beam, said beam receiver 47 including sensor elements 95-103 for receiving and sensing the laser beam radiated from the aforesaid beam sender 45, and a signal generator 118 responsive to the signals from the said sensor elements and which transmit the signal in accordance with the sensor element receiving the laser beam, a monitor device 154 provided independently of the beam receiver 47 comprising a receiving section 155 and an indicating section 157, said receiving section 155 including at least two photo-diodes 165, 167, said photo-diodes being connected to said indicating section 157 so that the laser beam radiated from the beam sender 45 may pass midway between the photo-diodes 165 and 167 of the beam receiver 155.