<title>Application of a ring laser for measurement of track geometrical parameters</title>

Abstract

Over last years, the ring lasers are wildly used as sensors of inertial measuring and navigational systems, due to such exceptional properties, as high accuracy, wide dynamic range, non-sensitivity to linear acceleration, et a!. In the conditions of growing speeds and density of railway traffic, growing requirements to accuracy of measurements, the systems on ring laser gyro (RLG) and accelerometers seem to be the most promising. Track checking includes the use of track measuring cars or carriages automatically recording the railway condition control of the railway under a load by the use of specialized track measuring vehicles equipped with computers for registration and analysis of measurement results.Although the ring laser gyroscope provides a very high accuracy in the measurement of angular rates and angles, it does have one significant problemsynchronization of the counter-propagating waves. This effect is usually referred to as lock-in. There were many solutions to the lock-in problem, but mechanical dithering of the RLG was finally adopted as a practical solution to it.If to use a constant displacement of RLG output characteristic (nonreciprocal element or rotating with constant rate), it will be rather difficult to ensure stability of its magnitude and to measure an instantaneous value of output frequency with an adequate accuracy. At use of a variable initial displacement, the output RLG signal is usually the phase, accumulated during one or few period of displacement. In this case the simplified schematic of the ring laser may be preseifled, as shown in fig. 1, where 01(t,) is quantized value of measured angle 0. pe(p)RLGç2 01(tj) Fig. 1. The transfer function of such element looks like W1(p) = Ku(.T), p where: KIG 5 the RLG scale factor; T1 =T , ifonly one reverse counter is using in the channel ofthe ring laser and T1 = % , if two reverse counters are using.The spectrum of such element output signal in basic is determined by the frequency of quantization fk = 1/T1 . Schematic of the ring laser channel with dither is shown in fig. 2. HI%.RLG o (t1) Fig. 2. The corresponding transfer function is RW W2 (p) = exp(-piT1), p(T2p + l)(Tp2 + 2T2p + 1) where: T2 is the dither mechanical time constant.Some solutions, suggested by authors, concerned with providing of high angle resolution and measurement of angles, changing with high frequency are given in1.The track measuring car in the most general case has three RLG and three accelerometers. Their input signals look in this case as follows2:= ji cos 0 + K sin 0 cos y + E cos p(sin0 cos y cos K -cos 0 sin K) -E sin p sin0 cos y - V(1) cos y(cos 0+ tg p cos y sin K sine),