JPS61145460A - Speed detection circuit - Google Patents

Abstract

PURPOSE:To enable the rapid calculation of a speed, by counting the number of pulses of a rotary encoder within a definite time DELTAt and calculating the change DELTAtheta in a rotary position within said time DELTAt while detecting a speed by DELTAtheta/DELTAt. CONSTITUTION:A pulse is generated at every definite rotary angle from a rotary encoder 2 and inputted to a wave form shaping/rotary direction discrimination circuit 3 to discriminate a rotary direction and a shaped pulse 9 is counted. Next, a counter 7 counts a clock pulse generated from a reference frequency oscillator 6. The circuit 4 counts the rotary pulse from the encoder within a time from a start signal 11 to a stop signal from a count number discrimination circuit 8 and a clear signal 13 is generated from the circuit 8 and the count value of the counter 4 is inputted to a register 5. The register 5 stores the number of rotary pulses at every DELTAt-time and a microprocessor calculates the change DELTAtheta in the rotary position within the DELTAt-time and a motor current I is calculated from DELTAtheta/DELTAt by a specific formula to control the output of the motor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical Field The present invention relates to a speed detection circuit in servo control.

Servo control is one form of automatic control technology that controls the positioning of robot arms and machine tools by driving motors and the like.

In servo control, the current position and current speed are constantly detected and the power is adjusted as a function of the position deviation and speed.

B) Conventional technology and its problems In servo control, for example, the current position of a robot arm or machine tool is detected by some method, and the motor, etc. Adjust the driving force.

This will be explained using a motor as a general power source as an example.

The current rotational position of the motor shaft is θ, and the target position is θ!
, let J be the constant of proportionality. The current value I given to the motor is
The simplest calculation is I=J(θ!-〇)(1). However, the current I is assumed to be positive if it flows in the direction in which the position θ of the motor shaft increases. (1
) When a current is applied as shown in the equation, the rotational position 0 of the motor shaft becomes
When the motor is far from the target position θ, a large current flows in order to rotate the motor in a direction closer to the target position θ. The driving force of the motor decreases as the target position is approached. Target value θI
When this happens, the motor driving force becomes zero. In this way, θ becomes θ! can be approached. Since there is resistance in the motor itself and the reduction gear load, θ approaches θL while vibrating.

However, in the case of equation (1), the speed at that time, that is, the rate of change in θ is not taken into consideration. For this reason, resistance (damping) proportional to speed is insufficient, and θ becomes the target value θ.
Vibration may occur near I.

Therefore, it is common to add a compensation term proportional to the current rotational speed (dθ/d[).

In other words, the driving force is given as follows. Kv is a constant. The negative sign in front of this means that force is applied in the opposite direction to the speed.
In other words, it means adding braking force. (2
) is the most commonly used servo control equation at present.

A potentiometer can be used to detect the rotation angle θ. The rotation speed (dθ/dt) can be detected by a tacho generator. Both are analog detection.

A servo control circuit can be constructed by combining these analog sensors with a suitable operational amplifier.

Advances in integrated circuit fabrication technology have made microprocessors available at low cost in recent years.

So-called software servo, in which the current control expressed by equation (2) is also calculated by a microprocessor, is becoming popular.

In addition to the basic term expressed in equation (2), external forces such as the mold blade, etc.
Adding correction terms such as inertial force can be easily done by changing the software.

Therefore, software servo control enables more accurate control.

Furthermore, in the case of software servo, the rotational angular position θ of the rotating body can be detected digitally. This is because all data processing after the sensor is digital processing. If the angular position θ is detected by an analog sensor such as a potentiometer, the A/
After D conversion, it must be input to the microprocessor.

Therefore, it is more convenient to perform the position detection itself digitally. Therefore, the rotary encoder can be used for angular position detection.

A rotary encoder generates one pulse for every certain minimum angle unit ε, and the number of revolutions can be determined by counting the number of generated pulses. The smallest angular unit can be made as small as desired. Therefore, the measurement accuracy is significantly higher than that using an analog sensor.

Conventionally, θ and (dθ/d[) were measured using different detectors. However, in the software servo system, the velocity (dθ/d() is not directly measured, but is often calculated from the angular position data θ.The simplest method is
From the current position θit), subtract the position θ(−Δt) at the previous sampling time, which is stored in the memory.
The result obtained by dividing this by the sampling time Δt is the differential, that is, the velocity.

In this case, the coefficient Kv of the speed-based correction term in equation (2) may include 1/Δt.

When approximated as shown in equation (3), the angular position θ([) at each sampling time must be stored in the memory. Then, θ((-Δt)) is read out from the memory and the calculation in (3) is executed.Due to the memory access time and calculation, the time interval for outputting ■ becomes long.

The performance of servo control is better as the time interval between outputting ■ to the motor is shorter. Therefore, it is unacceptable to say that it takes a long time to calculate (3).
The purpose is to detect the target speed (dθ/dt) within a short time, quickly calculate equation (2) using a microprocessor, and perform servo control with quick response.

If a speed sensor were provided, it would be possible to detect the speed in a short time, but instead of using a speed sensor, the speed is determined by an electronic circuit, that is, by hardware. Reduces the burden on the microprocessor and improves servo control performance.

(:I-) Configuration In the present invention, a rotary encoder is used to detect rotation. A rotary encoder produces pulses for constant micro-rotations. By counting and integrating the number of pulses, the rotation angle position θ can be determined.

The speed can be determined by counting the number of pulses generated within a certain period of time without integrating them. Input the speed data as is into the microprocessor, and (2)
Used in formula calculations.

The rotary encoder is connected directly to the motor or via a speed reducer or speed increaser.

Assume that the rotary encoder generates one pulse every time the motor shaft rotates by ε.

If m pulses are generated within a certain time Δt, the motor shaft rotates by mε within this time Δt. Then mε/Δt gives the rotational speed.

Here, the m number of pulses takes into consideration positive and negative pulses. The positive rotation pulse is (+1) and the negative rotation pulse is (-1), and the sum of these is m. m
can be positive or negative.

On the other hand, in the case of rotational displacement, if the initial displacement is θ0 and the sum of subsequent positive and negative pulse count values is M, then the current angular position θ is determined by the following equation: θ=θo+Mε (4).

Divide the time axis by Δt. 1.2.・・・・・・Add a suffix of j. Representative times of this area are tl, t2, song...
[Write it as j.

tj=jΔt(5). It is assumed that rnj is the algebraic sum (number of positive pulses−number of negative pulses) of the number of pulses generated by the rotary encoder in the j-th time domain.

M in equation (4) is the sum of rnj, M(tj): k4, mk (6
) cj, motor position θj and motor speed (dθ
/dt)j is expressed by θj=θ0+, mi, mkε (7) dθ(dj=mjt/At.Δt, ε, and θ0 are constants.

From equation (8), it can be seen that the speed can be immediately obtained by counting the number of pulses of the rotary encoder for 61 hours.

The derivation of speed using formula (3) conventionally used in software servo is as follows: mj = M(tj) M(Lj-t)
(9) is executed. In order to do this, the set (M(tj)) must be stored in memory, and it takes time to read it from memory, so it takes a lot of time to calculate one fnj.

On the other hand, in the present invention, the speed is immediately known from equation (8).

FIG. 1 is a block diagram of a speed detection circuit according to the present invention.

Loads such as robot arms and machine tools, and motor 1 are
They are connected via a suitable speed reducer.

The rotary encoder 2 detects the rotation of the motor 1. The rotary encoder 2 and the motor 1 are coupled indirectly or directly via a transmission.

The rotary encoder 2 generates pulses at every fixed rotation angle. It is assumed that one pulse is generated each time the rotation angle of the motor reaches ε, including when the rotation angle is through a transmission.

Since the rotary encoder 2 needs to determine the direction of rotation, it actually produces two pulse trains. They are called pulse trains A and B. These are shifted by 1/4 period from each other.

Since pulse train A or pulse train B precedes the rotation direction, it is possible to determine whether the rotation direction is positive or negative. To detect the rotational speed, it is sufficient to count only one of the pulse trains.

Pulse trains A and B are pulse trains that are generated one by one every rotation of the motor ε, and these pulse trains are input to the waveform shaping rotational direction determination circuit 3.

Here, the rotation direction of the rotary encoder is known. The counter 4 counts pulses in the positive direction as (+1) and pulses in the negative direction as (-1).

The rotation direction is determined by checking which of the pulse train A and pulse train B comes first. For example, a waveform is created by differentiating pulse train A. Since this becomes a positive pulse at the rising edge and a negative pulse at the falling edge, the negative pulse is dropped through the diode. The product of pulse DA and pulse B is calculated.

When pulse train A is leading, the product DAXB is zero.

When pulse train B is leading, the product DAxB has a short pulse waveform. When this is input to a one-shot multivibrator, an output value "'1" can be obtained. In addition to this, various rotational direction determination circuits are possible.

Waveform shaping involves changing the pulse to a sharp rise or fall in order to input it into a pulse, and a one-shot multivibrator is often used to create a pulse train with the same pulse width.

Counter 4 is an up/down counter.

Based on the rotation direction determination signal 10, if the rotation is positive, the count is up-counted, and if the rotation is negative, the count is down-counted. Counter 4 counts shaped pulses 9.

This is the first counting circuit, and is used to determine the rotation speed of the motor.

By integrating the rotation Δ0 of the motor, the current angular position θ([) of the motor can be determined.

Next, there is a second counting circuit which is to measure the time. A reference frequency oscillator 6 produces clock pulses of frequency f. This is a pulse for timekeeping.

A counter counts this clock pulse.

Assume that n pulses are generated during a unit time Δt.

Δt=-αQ It is. Let the count value of the counter be X.

X can take values from 0 to (n-1). During this time, a time period Δt elapses.

The count determination circuit 8 inputs the start signal 11 to the power counter 4 when x=Q. At this moment, the counter 4 starts counting rotational pulses from the rotary encoder.

The count determination circuit 8 inputs a stop signal 12 to the counter 4 when x==n. At the same time, the reset signal 14 is given to the counter, and the data of the counter 7 is @
0". That is, -=n is equal to x = Q. From x = Q to x = n, a time of Δ has elapsed.

Therefore, if the count value of the counter 4 is m at this time, mε is the rotation of the motor that occurred within Δt. If this is Δθ, then Δθ=mε (b).

Subsequently, the count number discrimination circuit 8 inputs the clear signal 13 to the counter 4. As a result, the count value m of the counter 4 is input to the register 5, and at the same time, the data of the counter is reset to 60''.

Register 5 stores the number m of rotational pulses within Δt. This is read into the microprocessor.

This is repeated every Δ(time).

In this way, data such as ml, m2, . . . are input to the microprocessor. From the value of m, the microprocessor immediately calculates, using equation (8),
From the speed at that time and the integrated value of m, the angular position θ at that time is determined by equation (7).

From these values, the motor current l is calculated using equation (2), and the motor output is controlled.

The count determination circuit 8 is considered to be a control circuit that operates the counter 4 continuously for a period of Δt to obtain the number of pulses m corresponding to the angle change Δθ within Δt. be able to.

Since the count determination circuit 8 is a circuit for comparing the magnitudes of X and n, it can be constituted by a comparator.

Simply put, the counter 7 and count number discrimination circuit 8 are
It can also be configured with one counter element and several logic gate elements, or one counter element.

E) Effects (1) The speed (dθ/dt) can be determined simply by counting the number of rotary encoder pulses within a certain period of time Δt. Store the data of position θ in memory,
There is no need to calculate it now. The burden on the microprocessor is reduced. Speed can be quickly determined.

(2) Therefore, the burden of calculating the motor current or driving force (2) is reduced, the calculation time is shortened, and the sampling time is shortened. Therefore, servo control with good performance is possible.

(3) The only sensor required is a rotary encoder.

Two sensors measuring angular position and velocity are not required. The cost is reduced by this amount.

(4) The circuit required here is TTL, 0MO5
It can be easily configured using commercially available logic ICs such as .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a speed detection circuit according to the present invention. 1...Motor 2...Rotary encoder 3...Waveform shaping rotation direction determination circuit 4...
・Counter 5...Register 6...Reference frequency oscillator 7...Counter 8...Count number discrimination circuit Inventor: Kenji Okamoto

Claims (1)

[Claims] A first counting circuit that counts the pulse train generated in the rotary encoder including the sign using a positive/negative rotation direction discrimination signal, a second counting circuit that counts the pulse train from the reference frequency oscillator, and a second counting circuit that counts the pulse train from the reference frequency oscillator. It consists of a control circuit that operates the first counting circuit for a fixed time interval Δt from the count value of the counting circuit, and by counting the pulse train of the rotary encoder, including the sign, for a fixed time Δt, it is possible to calculate the number of pulses within this time. A speed detection circuit characterized in that a change in rotational position Δθ is determined and a speed is detected by (Δθ/Δt).