JPS5918665B2 - Speed detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an encoder that outputs two sinusoidal voltages with an electrical phase difference of π/2 rad to obtain a smooth speed signal voltage even at low speeds. This relates to a speed detection method that can be used, for example, N/Clli
This method is highly effective when used to detect the speed of a drive shaft driven by a control device.

Conventionally, a tacho generator, which is a direct current generator, has generally been used to detect the speed of a drive device whose speed is controlled by an N/C control device, etc. However, the tacho generator has a complicated structure and is expensive. Since it has a commutator and bushing, there were problems with its durability and the reliability of the voltage detected due to poor contact in this part.

As one means for improving this, a method of detecting speed using an optical encoder as shown in FIG. 1 has been proposed.

In Fig. 1, reference numeral 1 denotes an optical shaft encoder that detects the rotation of a rotating shaft 20, which is printed with an opaque grid 3 at equal pitches, a glass disk 2 attached to the rotating shaft 20, and a light-emitting diode, etc. A light source 4, a condensing lens 5 that collects this light and irradiates it onto the glass disk 2, and a condensing lens 5 that receives this light through the glass disk 2, and as the glass disk 2 rotates, an opaque lattice is formed. It is composed of a solar cell 6 that converts the varying amount of received light into an electrical signal between the portion 3 and the transparent portion.

T is a comparator, which converts the voltage e, which is the output of the solar cell 6, which changes in a sinusoidal manner as shown in FIG. 2, to its center voltage V. 3, and converts it into a digital signal voltage as shown in FIG. 8 is an F/V converter that converts the frequency of the digital signal voltage output from the comparator T into an analog voltage.

In the device configured as described above, a digital signal voltage with a frequency proportional to the rotational speed of the rotating shaft 20 is obtained as the output of the comparator 7, and this is converted into a voltage proportional to the frequency by the F/V converter 8. As a result of the conversion, this output becomes a voltage proportional to the rotational speed, and in this way, the rotational speed of the rotating shaft 20 can be detected using an optical shaft encoder.

However, the speed signal voltage detected by this method is
When the rotational speed of the rotating shaft 20 becomes low, the ripple becomes large, and there is a drawback that good speed controllability cannot be obtained at low speeds.

For example, when performing control to stop the rotating shaft 20 at a fixed position, the speed control performance at low speed just before stopping is poor, and it is difficult to control the rotating shaft 20 to stop smoothly at a fixed position.Practical use It was an obstacle to doing so. This invention was made in view of the above points, and aims to provide a speed detection method using an encoder that is inexpensive and reliable, and that can obtain a voltage proportional to the speed with less ripple even at low speeds. It is something. FIG. 4 shows an embodiment of a method for detecting rotational speed using the method of the present invention using the output of an optical shaft encoder that is generally used for position detection in N/C control devices, etc. The same reference numerals as in the conventional example indicate the same or corresponding parts.

To explain the differences between Fig. 4 and Fig. 1,
1A is 1 of the pitches of the lattice 3 printed on the glass disk 2.
/4 staggered: solar cells 6A and 6
An optical shaft encoder with a rotary shaft 20
As shown in Figure 5, as the rotation of the
It outputs sinusoidal voltages El and e2 with a phase difference of d. 10A is a differentiating circuit for short-time differentiating the outputs El and e2 of the encoder, and is composed of an operational amplifier, a capacitor, and a resistor.

14 is a filter circuit that removes the DC component of the other output E2, and 15 is a division circuit that divides the output of the differential circuit 10A by the output of the filter circuit 14.

Note that each of these arithmetic circuits is desirably constructed from a one-chip integrated circuit. The operation of this device is as follows: the outputs of the filter circuit 14, the two voltages, are from the two equations, and the differentiating circuit 10
Output of A! l-! −1:″e1 is the formula (3) DtKnn
O″ is 1・COS−・θ, so 2T of the divider circuit 15
9. The output voltage is determined by the following formula.

Here, again, n/2π (this is a constant determined by the structure of the thick encoder 1A, so this value e1
●? is proportional to the rotational speed θ.

E2-VO The embodiment described above uses an optical shaft encoder for position detection, so the entire device can be miniaturized.
Although it is effective in reducing costs, it is also possible to have a dedicated encoder instead of also using a position detection encoder.Also, it can be used not only to detect the speed of a rotating body by using a shaft encoder, but also to detect linear motion. It goes without saying that the method of the present invention can also be used to detect the speed of an object to be measured.

Furthermore, encoders are not limited to optical encoders.
mutually π/2rad. An encoder that outputs two sinusoidal voltages with an electrical phase difference of , can similarly obtain a voltage proportional to speed. As explained above,
According to the speed detection method according to the present invention, the output from the encoder is not first digitized as in the past, but it is directly digitized.
Since it is processed by arithmetic processing, it is possible to obtain a voltage proportional to the speed with little ripple even at low speeds, and therefore extremely smooth speed control is possible using this signal. In particular, in control that performs fixed position stopping, smooth speed control is possible until the speed is low just before stopping, so stable and smooth fixed position stopping control can be performed, and the method of this invention can be used. The effects on the quality and economy of the device are extremely large.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of a method for detecting speed using a conventional optical shaft encoder, Figure 2 is a diagram showing the output waveform of the encoder, and Figure 3 is the output waveform of the comparator. FIG. 4 is a block diagram showing an embodiment of the present invention using an optical shaft encoder, and shows a method for detecting rotational speed. FIG. 5 is a diagram showing the output waveform of the encoder.
In the figure, the same reference numerals indicate the same or equivalent parts, 1 and 1A are optical shaft encoders, 2 is a glass disk, 3 is its lattice, 4 is a light source, 5 is a condenser lens, and 6, 6A, and 6B are solar cells. , 10A is a differentiating circuit, 12 is an addition circuit, 13 is a square root circuit, 14 is a filter for removing DC component, 15
2 is a division circuit, and 20 is a rotation axis.

Claims (1)

[Claims] 1 Using an encoder that outputs two sinusoidal voltages with an electrical phase difference of π/2 rad, one of the outputs of this encoder is time differentiated, the AC component is extracted from the other, and the former (differential output ) is divided by the latter (AC output) to obtain a voltage proportional to the speed that is input to the encoder.