GB2105477A

GB2105477A - Measuring speed and acceleration using a differential transformer transducer

Info

Publication number: GB2105477A
Application number: GB08224924A
Authority: GB
Inventors: Claude Raymond; Robert Chase; Andreas Weitsch
Original assignee: Sentec AG
Current assignee: Sentec AG
Priority date: 1981-09-04
Filing date: 1982-09-01
Publication date: 1983-03-23
Also published as: DE3232425A1; GB2105477B; FR2512555A1; FR2512555B1; JPS5873873A; CH644698A5

Abstract

The sensing element of a differential transformer transducer is rigidly attached to a movable element of which one wants to know the speed. The primary winding of the transformer is excited by a triangular wave (a) so that the derivative of this wave appears at the output of the secondary winding of the transducer as a rectangular wave (b). Samples are periodically taken of the amplitude of successive pulses of the curve (b) and differences ( alpha , beta ) between these values are also taken which are a measurement of the position of the movable element. Provided the time interval separating successive measurements is constant, the value of the differences ( alpha , beta ) represent the speed of the movable element during the time separating the two measurements. By taking the differences of these differences information can be obtained representing the variation of the speed of the movable element, i.e. acceleration or deceleration. <IMAGE>

Description

SPECIFICATION Utilization of an electronic tranducer for the measurement of the instantaneous speed and/or of the instantaneous variation of speed of a movable element with determination of the position thereof Background of the invention a) Field of the invention The present invention relates to the utilization of an electronic transducer of the variable differential transformer type to measure the instantaneous speed and/or the instantaneous variation of speed of a movable element, while measuring its position.

b) Description of the prior art The electronic transducers of the variable differential transformer type are known per se.

One of them is represented in view in Fig. 1 and partially and diagramatically in Fig. 2. Such transducers comprise a cylindrical casing 1 inside of which slides a ferromagnetic core 2, having the shape of a bar, and which is rigidly connected to a rod 3, that protrudes out of the casing 1, and which constitutes the sensing element of the transducer. The ferromagnetic core 2 moves in a primary coil 4, which is situated in respect to a secondary circuit 5 made of two coils 5a and Sb mounted in bucking, represented in Fig. 2 as being situated opposite the primary coil 4 but which, in reality, surround the latter.

The electronic transducers of the above mentioned type serve to measure the dimensions or the positions of an element, as does a mechanical comparator. They are used by exciting the primary winding 4 of the differential transformer with a sinusoidal wave. The variations of the position of the magnetic core 2 inside the primary coil 4 produce an unbalance of the secondary circuit 5. The conventional electronics of the apparatus, not represented in the drawings since it is known per se, is arranged in such a way as to demodulate the sinusoidal signal appearing at the output terminals of the secondary circuit 5 and to transform it into a direct current or tension, the value of which is representative of the position of the sensing rod 3 and, consequently, of the position or of the dimension of the element with which the said sensing rod 3 is in contact.

Summary of the invention The purpose of the present invention is to permit a new utilization of such an apparatus by means of a mere modification of the way with which it is excited, to know the instantaneous speed and, with a mere modification of the way the information relative to the speed are treated, to know the instantaneous variation of the speed.

The new utilization of an electronic transducer for measuring the instantaneous speed of a movable element is characterized by the fact that the sensing member of the transducer is coupled rigidly to the said movable element, and one excites the transducer by means of a triangular wave of current, so that the first derivative of this wave, which appears at the output of the secondary winding of the transducer, appears as a rectangular wave, then periodically taken samples of the amplitude of the said rectangular wave are a measurement representative of the instantaneous position of the movable element, and in such a way the difference of the measured values appearing between two measurements indicates the variation of position of the movable element which occurred in the time separating the said two measurements and consequently represents the instantaneous speed of the movable element.

The utilization of an electronic transducer to measure the instantaneous variation of the speed of a movable element is characterized by the fact that one couples the sensing member of the transducer rigidly to the said movable element, excites the transducer by means of a triangular wave of current, so that the first derivative of this wave, which appears at the output of the secondary winding of the transducer, appears as a rectangular wave, then periodically taken samples of the amplitude of the said rectangular wave are a measurement representative of the instantaneous position of the movable element, so that the difference of the measured values appearing between two measurements indicates the variation of the position of the movable element which occurred in the time separating the said two measurements and consequently represents the instantaneous speed of the movable element, and in which one calculates electronically the differences between the speeds, corresponding to different positions of the movable element, these differences represent the instantaneous variation of speed of the movable element.

The various features of the invention will be apparent from the following description, drawings and claims, the scope of the invention not being limited to the drawings themselves as the drawings are only for the purpose of illustrating ways in which the principles of the invention can be applied. Other embodiments of the invention utilising the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

Brief description of the drawings Except for Figs. 1 and 2 which represent the known transducer, the drawing shows the mode of utilization of the apparatus which is object of the invention.

Fig. 3 is a diagram of the excitation current of the transducer and of the first derivative appearing at the output of the secondary winding of the differential transformer, and Fig. 4 illustrates schematically the electronics of the transducer permitting the measurement of the instantaneous variations of the speed of the movable element.

Description of the preferred embodiments In view of the measurement of the instantaneous speed and/or of the instantaneous variation of the speed of the movable element, one couples the rod 3 of the transducer rigidly to the movable element so that the said rod follows the displacements of the movable element.

One applies to the primary coil 4 of the transducer not a sinusoidal wave, as in the conventional utilization of the tranducer, but a triangular wave, illustrated by the curve a of the portion A of Fig. 3. The first derivative of the excitation wave appears at the terminals of the secondary circuit 5. When the rod 3 is not in movement, this derivative looks like the curve b of the portion B of Fig. 3, that is to say appears as a series of rectangular pulses all of the same amplitude. The displacements of the movable element and, consequently, of the rod 3 and the ferromagnetic core 2 of the transducer, produce variations of the output of the secondary circuit 5 in the form of amplitude variations of the curve!;, indicated at!;' and!;" in Fig. 3.

Successive samplings are taken in phase with the curves a and!;, at intervals of 100 microseconds for instance, of the amplitude in one of the half periods of the curve b for each period. In the example represented, these samplings, indicated by references b1, b'1 and b"1, are taken on the negative phase of the pulses, but they could also be made on the positive phase, even on both phases. It is only necessary to take care that the period separating two samplings of information be perfectly constant.

The amplitudes measured are representative of the position of the movable element at the moment of each sampling, consequently of each instantaneous position.

The difference of amplitudes between two consecutive measurements indicated by a in the case of b'1-b1 and by p in the case of b"1-b'1 is obviously function of the displacement of the movable element during the time which has lapsed between these two measurements. If the time which lapses between the different measurements is constant, this difference is directly representative of the instantaneous speed of the movable element, that is to say of its speed during the time separating two measurements.

It is sufficient to have the electronics of the apparatus capable to form the differences of these differences, by means of memories, as shown in Fig. 4, so that the data treated this way be no more the image of the instantaneous speed of the movable element, but of the instantaneous variation of this speed, that is to say the acceleration of the deceleration of the movable element.

It is to be noted that, due to the excitation by a triangular wave and due to the synchronous sampling, the result of the measurements is much less sensitive to errors of dephasing as it would be the case of an excitation by a sinusoidal wave.

The new utilization of the electronic transducer will present numerous and diverse applications in the area of robots, machine-tools or civil engineering equipment, for instance, applications in which the output of the apparatus can be used, by a feedback device, to control the movable element. This will permit to adjust the speed of the movable element according to any desired program, especially as a function of the instantaneous position of this movable element.

Among the particularities of the applications of the present utilization, it is interesting to point out that it permits to stop a movement asymptotically, that is to have a movable element approaching a determined position at zero speed, contrarily to the control devices in which the arrival of the movable element at a given position starts the stopping procedure of the movement, with all the imprecisions which derive therefrom.

Claims

1. Utilization of an electronic transducer of the variable differential transformer type for the measurement of the position and of the instantaneous speed of a movable element, and in which one couples the sensing element of the tranducer rigidly to the said movable element, excites the transducer by means of a triangular wave of current, so that the first derivative of this wave, which appears at the output of the secondary winding of the transducer, appears as a rectangular wave, then samples periodically the amplitude information of the said rectangular wave, the measured values being representative of the instantaneous position of the movable element, in such a way that the difference of the measured values appearing between two measurements indicates the variation of position of the movable element which occurred in the time separating the said two measurements and consequently represents the instantaneous speed of the movable element.

2. Utilization of an electronic transducer of the variable differential transformer type for the measurement of the instantaneous variation of speed (acceleration or deceleration) of a movable element, in combination of the measurement of the position and of the speed of this element, in which one couples the sensing member of the transducer rigidly to the said movable element, excites the transducer by means of a triangular wave of current, so that the first derivative of this wave, which appears at the output of the secondary winding of the transducer, appears as a rectangular wave, then periodically taken samples of the amplitude of the said rectangular wave are a measurement representative of the instantaneous position of the movable element, so that the difference of the measured values appearing between two measurements indicates the variation of position of the movable element which occurred in the time separating the said two measurements and consequently represents the instantaneous speed of the movable element, and in which one calculates eiectronically the differences between the speeds, corresponding to different positions of the movable element, these differences represent the instantaneous variation of speed of the movable element.

3. Utilization of an electronic transducer for the measurement of the instantaneous variation of the speed of a movable element, in combination with the measurement of the position and of the speed of the element, substantially as herein described.

4. Utilization of an electronic transducer for the measurement of the instantaneous variation of speed of a movable element, in combination with the measurement of the position and of the speed of the element, substantially as herein particularly described with reference to the accompanying drawings.