JPH02503037A - Element that generates the tachometer signal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Element that generates the tachometer signal This invention includes a rotating connector and a generator with brushes for rotating the collector. Concerning the element that generates the tachometer signal, which generates a measuring voltage proportional to the speed. do.

A tachometer generator is used to measure the instantaneous rotational speed of an electric motor or transmission shaft. It is widely used in electric drives with servo systems.

According to the usual form of construction, these generators have a structure similar to that of a DC motor. , in which the stator is produced by a permanent magnet or by a winding fed with a constant current. The rotor has a winding connected to the commutator.

The commutator is connected to various parts of the rotor winding and stationary brushes that are integral with the stator. Contains a rotating collector with segments of thin plates connected, between which a tachometer signal appears. The brush collector assemblies have surfaces that slide against each other. ideally a semi-permanent and continuous property. Should.

As a practical matter, permanently maintain perfect contact between brush and collector This has proven to be very difficult, especially when the brush has very small dimensions. and when they are made of precious metals. to contact There is typically a very short interruption in the tachometer signal that causes a sudden drop in the tachometer signal. It has been found that this signal exhibits short-duration noise. . These noises are especially troublesome when the generator is used in a servo control loop. The reason is that they can considerably disturb the good functioning of the control.

To remedy this defect, the tachometer is It has been attempted to filter the signals of However, such a solution The solution comes down to severe limitations on the passband of the tachometer signal and therefore high performance drive. It cannot be applied to elements. In particular, this is the case in robotics applications, where Here the tachometer signal is also related to the natural frequencies of the various components of the mechanical structure. It is intended to be used to damp vibrations in kinematic chains. Ru.

The object of the invention is to remedy the above-mentioned deficiencies and to provide a simple and inexpensive solution. The purpose is to provide elements with a new configuration, which are suitable for contacting the collector of a generator. makes it possible to obtain a tachometer signal free of noise caused by interruptions in traffic.

For this purpose, the generator element according to the invention Maintains the value of the measured voltage during accidental interruptions of it resulting from full electrical contact. The passband for the tachometer signal is Upper frequency limit equal to or exceeding 1 kHz, outside the time of the break in the description. It is designed in such a way that it extends to the entire world.

According to one preferred embodiment, the sustaining circuit is implemented in series with the internal resistance of the generator. The device includes a capacitor, and the device has a voltage applied to the terminals of the capacitor. Contains a measurement circuit that always has a high input impedance. Furthermore, very high resistance A resistor with a capacitor may be mounted in parallel with the capacitor.

The features mentioned above, as well as other features and advantages of the invention, are illustrated with the aid of the accompanying drawings. It will become clearer from the following description of an illustrated exemplary embodiment.

FIG. 1 shows a block diagram of a known tachometer generator element.

2A and 2B illustrate the function of the elements of FIG. 1. FIG.

FIG. 3 is a block diagram of a first embodiment of a device according to the invention.

4A and 4B illustrate the function of the elements of FIG. 3. FIG.

FIG. 5 is a block diagram of another embodiment of a device according to the invention.

FIG. 6 is a block diagram of a typical application of the device of this invention.

Figure 1 shows a tachometer generator G producing a voltage Ut, which is located on the generator shaft. proportional to the rotational speed and it supplies a current i1, which is external for the generator form a load. Voltage signal U, is received at the terminals of resistor R2 and is applied to amplifier A, is applied to the input, and its output voltage is designated as Us.

In such a device, the current Lt is caused by an imperfect contour in the collector of the generator. The voltage Uj also changes at time t in FIG. 2A when subjected to a short interruption for the down to O for the corresponding passage of time, as illustrated at time t2 and time t8. Garu.

These voltage drops Ut are quite similar for the tachometer output signal of element U. have an influence. Therefore, these perturbations propagate downstream of the circuit in Figure 1 and cause the aforementioned defects. It will cause trouble.

FIG. 3 shows a first exemplary embodiment of the device of the invention which overcomes this drawback.

In Figure 3, the tachometer generator G is no longer connected to a resistive load and is It is connected to pacita C,. The internal resistance of the generator is represented by resistor R7, which is mainly formed by the winding resistance and the contact resistance between the brush and collector. It will be done. Typically, this internal resistance has a low value, corresponding substantially to the resistance of the winding. Kya The capacitance of the pacita C is such that the electrical time constant R1·C7 is constant for a few microseconds, for example. It is preferably selected in such a manner that it is relatively low. The amplifier used has a very high input is an operational amplifier A2 with a power impedance.

Under this situation, the circuit connected to the tachometer generator is In order to maintain the value of the voltage Ut during the period of interruption due to temporary incomplete contact, form a circuit. As illustrated in FIGS. 4A and 4B, the output voltage U , as well as the voltage Uc at the terminals of the capacitor C1 for a fraction of the time It is useful to maintain it at the same value that prevailed before. Figure 4A shows, for example ,1,) indicates an interruption that occurs at time,t,. During the interval t, between the brush and the collector contact is interrupted and the internal resistance R.

suddenly takes an infinite value, and further current IC is the load circuit of capacitor C1. can't flow into it. Therefore, the output voltage U of the operational amplifier is just During each break, the value corresponding to the value that prevails at the time of to and should not show any discontinuity cormorant.

No accidental interruptions during the normal functioning of the elements, i.e. in the collector of the generator When the passband for the tachometer signal is substantially unchanged by the circuit of the present invention. First, the capacitance of capacitor C7 is such that the upper frequency limit of the passband is at least selected in such a way that it has a value equal to 1 kHz and, in practice, generally considerably higher. be done. For example, if the internal resistance of the generator is on the order of 500 to 100Ω. If so, the capacitor used preferably has a capacitance of the order of 10 nF. . Under this situation, the current produced by the generator is at the input impedance of the operational amplifier. It is noteworthy that the dance is clearly extremely low, all the more so because it is extremely high. There will be.

FIG. 5 shows another embodiment of the device of the invention, in which a very high resistance is applied. A resistor R, with a resistor R, is implemented in parallel with a maintenance capacitor denoted C2. this thing is when the input voltage of the operational amplifier, denoted A, is between the collector and the brushes of the generator. Measures to prevent having an infinite value in case of mechanical breakage of electrical connections provide. The resistance R, preferably has a value on the order of megohms. Generator In case of a break in the connecting wire between the and measuring circuit, the voltage applied to the input of the operational amplifier gradually decreases to 0 due to the presence of the resistor R,.

FIG. 6 illustrates an example of the application of the device of the invention, according to which the device can be used in electric motors. It is part of the control loop for controlling speed. For example, a DC motor Eel motor M is power amplifier A! sent via. The shaft of the motor is the shaft of the generator G. integrally, so that the signal Ut generated by the latter is proportional to the rotational speed of the motor. Give an example. This signal is applied to the input of operational amplifier A4, which is also the input of control amplifier A4. Fulfill function. Capacitor C1 is the electrical contactor in the commutator of the generator. 3 in a similar manner to eliminate possible noise effects from interruptions in the It is connected to that of Yapacita C7.

A voltage U" with a reference value is applied to the second input of the amplifier A4 via a resistor R, It will be done. Any difference between the reference value U, and the value of the voltage Ut of the tachometer signal increases is sensed and amplified by amplifier A4, which in turn is fed to power amplifier AS. generates a correction signal. The negative feedback circuit z1 can be a normal Designed in a manner.

! international investigation report international search report CH8900013 SA 26317

Claims (3)

[Claims] 1. Generates tachometer signal including generator with rotating collector and brushes A device that provides a measurement voltage proportional to the rotational speed of the collector. In what If it occurs from incomplete electrical contact between the brush and the collector, Contains circuitry to maintain the value of the measured voltage during periodic interruptions, and this circuitry whose passband for the data signal is equal to 1 kHz outside the time of said interruption. an element characterized in that it extends to an upper frequency limit at or above the frequency limit; 2. that the sustaining circuit includes a capacitor mounted in series with the internal resistance of the generator; The capacitor contains a measurement circuit with a very high input impedance and 2. According to claim 1, characterized in that the voltage appearing at the terminals of the terminal is applied to it. Motoko. 3. Particularly, a resistor with very high resistance is mounted in parallel to said capacitor. 3. A device according to claim 2, characterized in that it has the following characteristics: