DE10042007A1 - Device and method for measuring angles - Google Patents

Abstract

The invention relates to a device and to a method for measuring angles, comprising at least two sensor elements that are arranged relative to each other at a predetermined angle and that scan a rotating element that is provided with periodic marks. Depending on output signals (C, S) of the sensor elements available as voltages, synthetic signals (Cp, Sp, Cm, Sm) are produced that correspond to an angle modulation, and the output signals are compared with said synthetic signals (Cp, Sp, Cm, Sm) to determine the angle.

Description

State of the art Absolute angle sensors based on the AMR or Hall principle

There are arrangements of AMR (anisotropic magnetic resistance) sensors or known from Hall sensors, with the help of which the absolute direction of a external magnetic field can be determined. Here, two AMR sensors that are arranged at an angle of 45 ° to one another, or two Hall sensors, which are arranged at an angle of 90 ° to each other. The External magnetic field is usually generated by a rotatable permanent magnet provided, the angular position of which is to be determined. An example of such The sensor arrangement is the AMR sensor KMZ 41 from Philips.

The electrical signals C, S supplied by such sensors have the form:

C (Φ) = A.cos (Φ)
S (Φ) = A.sin (Φ)

Here A is the amplitude and Φ is the angle to be determined. At the Hall The sensor, the magnetic field angle is identical to Φ, for the AMR sensor it is Magnetic field angle equal to Φ / 2. Evaluation methods for determining Φ are z. B. described in DE-OS 195 43 562.

Incremental angle sensors

A wide variety of incremental angle sensors are known, based on optical ones or magnetic principles work.

In the case of optical incremental angle sensors, a rotatable disc is included periodic line marks or a periodically broken disc illuminated and the resulting intensity fluctuation in incremental pulses implemented (application example: computer mice).

With magnetic incremental sensors, the field becomes a permanent magnet periodically through the teeth of a rotatable ferromagnetic gear modulates what is in a Hall or AMR / GMR (giant magnetic resistance) - Sensor is detected and converted into incremental pulses.

Object of the invention

The invention combines the AMR or Hall Angle sensors with the idea of an incremental evaluation without the With the help of additional mechanical elements such. B. gears. In the incremental evaluation, the frequency is the delivered Incremental pulses proportional to the angular velocity.

Incremental angle sensors can be used e.g. B. as a wheel speed sensor for ABS / FDR, as engine speed sensor or as steering wheel angular speed keitsgeber.

Core and advantages of the invention

The invention enables simple and inexpensive incremental Evaluation of angle sensors according to the AMR (GMR) or Hall principle. The mechanical structure corresponds to that of the absolute described above Angle sensors (AMR or Hall sensor arrangement with rotatable Permanent magnets). The elaborate determination of the angle Φ from the analog sin / cos signals are not required.

Compared to optical or magnetic incremental angle sensors the advantage that no additional mechanical components such as optical Disc or ferromagnetic gear are required.

Compared to optical incremental sensors are magnetic Incremental sensors are much less susceptible to contamination and for harsher operating conditions.

There is also the advantage that the number of dispensed Incremental pulses per revolution need not be an integer. The angles Resolution ΔΦ, which corresponds to a given incremental pulse, is almost freely selectable. In the known arrangements, however, the number the incremental pulses per revolution by dividing the optical disc or the gear.

Description and drawings

When the device is switched on, the two instantaneous sensor output signals C ₀ , S ₀ , which correspond to the sensor angle Φ ₀ prevailing at the time of sampling, are held in two sampling / holding elements:

C ₀ = A.cos (Φ ₀ )
S ₀ = A.sin (Φ ₀ )

The current sensor signals C and S are compared by comparators with synthetic signals which are determined from C ₀ and S ₀ . The synthetic signals Cp, Sp and Cm, Sm describe the values of C and S after an angular advance by the selected increment ΔΦ (for Cp, Sp) and -ΔΦ (for Cm, Sm).

The following applies to the synthetic signals:

d. that is, the voltage values of the sample / hold elements are constant Factors cd and sd weighted, which, for. B. by resistors or switched capacitor (SC) structures can take place.

For the digital output signals k ₁ . , , k _{4 of} the comparators applies:

k ₁ = S <S _p
k ₂ = S <S _m
k ₃ = C <C _p
k ₄ = C <C _m

(Condition on the right side true: signal = 1, otherwise 0).
If the actual angle Φ exceeds the angle Φ ₀ + ΔΦ, then at least one of the signals k1, k3 is expected to topple over. If the angle falls below the angle Φ ₀ - ΔΦ, one of the signals k2, k4 is expected to topple over.

With the help of two further digital comparator output signals, it can be decided which signal is expected to topple over and what the direction of the overturning will be (0 = <1 or 1 = <0):

k ₅ = (S ₀ + C ₀ ) <0

k ₆ = S ₀ <C ₀

Using simple digital logic, the two incremental clock output signals T _left and T _right (for the two possible directions of rotation) are now generated from the comparator signals k ₁ to k ₅ :

In the case of a rising edge from T _left or T _right, a monoflop circuit generates a renewed sampling pulse for the sampling / holding elements, which saves the new angular position that has now been reached, and the whole process begins again.

If the angle is not changed for a long time, it can happen that the Signals in the sample / hold elements drift away due to leakage currents. It is therefore provided that a time monitoring circuit after the Time T0 (e.g. 10 seconds) in which no change in angle was detected, generates a sampling pulse that refreshes the sampled signals. No increment clock signal is generated here.

Figure 1 shows the block diagram of the invention. The differential sensor signal pairs C ₁ , C ₂ or S ₁ , S ₂ are fed to two differential amplifiers which, after deduction of any offsets of the sensor, deliver the signals C and S described above. This is followed by two sample / hold elements, which deliver the held signals C ₀ and S ₀ . A resistance or SC matrix in connection with 6 comparators supplies the logical signals k ₁ to k ₅ , which are further processed in a logic. The incremental clock output signals T _left and T _right and the scanning signal are generated in the logic. The scanning signal is e.g. B. from a monoflop with a fixed pulse duration of z. B. 20 microseconds. The time monitoring and reset circuit mentioned above is also in the logic block.

Figures 2 and 3 show an example of the wiring of the 6 comparators that generate the signals k ₁ to k ₆ .

Claims (2)

1. Device and method for angle measurement with at least two sensor elements, which are arranged at a predeterminable angle to one another and scan a rotatable body with periodic markings, characterized in that, depending on the output signals (C, S) of the sensor elements present as voltages, synthetic signals ( Cp, Sp, Cm, Sm) are formed, which correspond to an angle change and the output signals are compared with the synthetic signals (Cp, Sp, Cm, Sm) for determining the angle. 2. Device and method for angle measurement according to claim 1, characterized in that the comparisons in Comparators run and the voltage values of the signals in Sampling and holding elements can be stored.