SE1200025A1 - Monitoring of resolver cable disconnection - Google Patents

Abstract

To determine whether a resolver cable is disconnected or broken, reference voltages (170, 180, 190) are applied to comparator terminals (80, 90, 100, 110) to displace the voltages fed into the comparators (120, 130) outside the interference range. Two measurements are obtained with displacement performed in opposite directions, and non-identical comparator values indicate a disconnected cable. (Figure 1)

Description

15 20 25 30 This object is achieved by the device according to appended claim l.

According to the invention there is provided a method for determining whether a first coil having a first and a second coil terminal is connected to a first comparator having a first and a second comparator terminal. The method comprises the steps of: providing an excitation signal configured to induce a first voltage difference between the first and the second coil terminals; providing the first comparator terminal with a first reference voltage; providing the second comparator terminal with a second reference voltage which is higher than the first reference voltage and obtaining a first comparator output value; providing the second comparator terminal with a third reference voltage which is lower than the first reference voltage and obtaining a second comparator output value; and determining on the basis of the first and the second comparator output values whether the first and the second coil terminals are connected to the first and the second comparator terminals or not.

By applying the reference voltages it is enabled to distinguish between interference and resolver signals with the help of cheap additional components.

Further advantageous embodiments of the invention are the subject of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in greater detail with reference to the accompanying drawings, where figure 1 shows a circuit diagram according to one embodiment of the invention, and 10 15 20 25 30 figure 2 shows a diagram illustrating normal working voltage of a resolver and voltage shifts.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to figure 1, a resolver 10 comprises two resolver signal coils, an x-coil 20 and a y-coil 30, which are excited by a rotating excitation coil (not shown). The resolver signal coils 20, 30 are arranged at 90 degrees angle in relation to the excitation coil such that the phases of the sine formed voltage amplitudes induced to the resolver signal coils 20, 30 are shifted by 90 degrees during rotation of the excitation coil. The x-coil terminals 40, 50 are connected to x-comparator terminals 80, 90 of an x-comparator 120 which outputs either one or zero as an x- value 140 depending on which one of the x-coil terminals 40, 50 has higher electric potential. The x-value 140 is inputted to a micro controller 160 which is able to determine the sign of the voltage difference between the x-coil terminals 40, 50. The y-coil terminals 60, 70 are connected in a corresponding manner, and consequently the micro controller 160 is able to indicate a quadrant which the excitation coil is facing. By counting the changes of quadrants the position and rotational speed of the resolver 10 can be determined.

If the resolver cable is disconnected or broken, interference from the surroundings causes weak signals to be inputted to the comparators 120, 130. The comparators 120, 130 can normally not distinguish between the interference and the resolver signals because they solely detect the sign of the voltage difference without considering the absolute value of the same. According to the invention the voltages inputted to the comparators 120, 130 are shifted outside of the range of the interference by reference voltages applied 10 15 20 25 30 on the comparator terminals. If the interference has an amplitude of 10 mV, it may be appropriate to shift the voltages by 20 mV in each direction. The shifting is done in positive direction by applying a first reference voltage 170 of 1,25 V in first and third comparator terminals 80, 100 and a second reference voltage 180 of 1,27 V in second and fourth comparator terminals 90, 110, and a first x-value 140 and a first y-value 150 are obtained. The shifting is then done in negative direction by applying the first reference voltage 170 in the first and third comparator terminals 80, 100 and a third reference voltage 190 of 1,23 V in the second and fourth comparator terminals 90, 110, and a second x-value 140 and a second y-value 150 are obtained. Change of the X- or y-values as a result of the voltage shifts indicates that the input signals are close to zero volts. If both the x-coil 20 and the y-coil 30 have input signals close to zero the conclusion is that the resolver 10 is not connected or the cable is broken.

Referring to figure 2, the excitation signal and the x- and y-coils 20, 30 are dimensioned such that maximum voltage differences induced between the x-coil terminals 40, 50 and the y-coil terminals 60, 70 are appropriate, such as about 1 V. A normal working range of the x- and y-coils can therefore be illustrated by a circumference of a circle 200 which corresponds to an arc tan function of the two voltage differences. If the resolver cable is disconnected or broken, the remaining interference corresponds to the small circle 210. The dotted lines 220 correspond to the shifted voltages, and the thickness of the dotted lines 220 corresponds to a hardware hysteresis at the comparators. The hysteresis is not necessary for the invention and can be omitted. The excitation signal may have any appropriate shape such as a shape of a sine curve. When the resolver 10 is working in a battery mode the excitation signal preferably consists of short pulses in order to prolong the battery time. Even more preferably the pulses have a relatively low frequency when the resolver 10 is in standstill or in quasi standstill, and the pulses have a relatively high frequency when the resolver 10 is rotating.

The invention is not limited to the embodiments shown above, but the person skilled in the art may modify them in a plurality of ways within the scope of the invention as defined by the claims.

Claims (1)

1. 0 15 20 25 30 CLAIMS A method for determining whether a first coil (20) having a first and a second coil terminal (40, 50) is connected to a first comparator (120) having a first and a second comparator terminal ( 80, 90), the method comprising the steps of: - providing an excitation signal configured to induce a first voltage difference between the first and the second coil terminals (40, 50); - providing the first comparator terminal (80) with a first reference voltage (170); - providing the second comparator terminal (90) with a second reference voltage (180) which is higher than the first reference voltage (170) and obtaining a first comparator output value (l40); - providing the second comparator terminal (90) with a third reference voltage (190) which is lower than the first reference voltage (170) and obtaining a second comparator output value (140); and - determining on the basis of the first and the second comparator output values (140) whether the first and the second coil terminals (40, 50) are connected to the first and the second comparator terminals (80, 90) or not. A method according to claim 1 comprising the step of: - determining that the first and the second coil terminals (40, 50) are connected to the first and the second comparator terminals (80, 90) if the first and the second comparator output values (140) are identical, and determining that the first and the second coil terminals (40, 50) are not connected to the first and the second comparator terminals (80, 90) if the first 10 15 20 25 30 and the second comparator output values (140) are not identical. A method according to any of the preceding claims comprising the steps of: - providing a second coil (30) having a third and a fourth coil terminal (60, 70), wherein the excitation signal is configured to induce a second voltage difference between the third and the fourth coil terminals (60, 70); - providing a second comparator (130) having a third and a fourth comparator terminal (100, 110); - providing the third comparator terminal (100) with the first reference voltage (170); - providing the fourth comparator terminal (110) with the second reference voltage (180) and obtaining a third comparator output value (150); - providing the fourth comparator terminal (110) with the third reference voltage (190) and obtaining a fourth comparator output value (150); and - determining on the basis of the first, the second the third and the fourth comparator output values (140, 150) whether the first and the second coil terminals (40, 50) are connected to the first and the second comparator terminals (80 , 90) or not. A method according to claim 3 comprising the step of: - determining that the first and the second coil terminals (40, 50) are connected to the first and the second comparator terminals (80, 90) if both the first and the second comparator output values (140) are identical and the third and the fourth comparator values (150) are identical, and determining that the first and the second coil terminals (40, 50) are not connected to the first and the second comparator terminals (80, 90 ) 10 15 20 if either the first and the second comparator output values (140) or the third and the fourth comparator values (150) are not identical. A method according to any of the preceding claims wherein a maximum first voltage difference is at least five times higher, such as at least ten times or at least twenty times higher, than a difference between the first reference voltage (170) and any of the second and the third reference voltages (180, 190). A method according to any of the preceding claims where the first coil (20) is a member of a resolver (10). A method according to claim 6 wherein the first comparator (120) is a member of a microcontroller (160) configured to receive revolution information from the resolver (10). A method according to any of the preceding claims wherein the excitation signal is provided to an excitation coil. A method according to any of the preceding claims wherein the excitation signal comprises a voltage pulse.