1. Field of the Invention
The present invention relates to a rotation angle detection device and, in particular, to a rotation angle detection device consisting of a stator, which is provided with an excitation winding of one phase and excitation windings of two phases, and a rotor having salient poles.
2. Description of the Related Art
An optical encoder has been conventionally used as a rotation angle detection device. However, the optical encoder has a disadvantage that its operating temperature environment is limited and, at the same time, it is complicated in its structure and is expensive. On the other hand, a rotation angle detection device utilizing a change in permeance of a gap between a rotor and a stator is devised as a rotation angle detection device that is simple in its structure and inexpensive and, at the same time, can stand even a high temperature environment. For example, an example of a rotation angle detection device having excitation windings of two phases and a one-phase output winding is described in JP 62-58445 B. In addition, an example of a rotation angle detection device having an excitation winding of one phase and two-phase output windings is described in JP 49-124508 A. In both of the conventional examples, since a rotor is formed to have salient poles, a phase or an amplitude of a voltage induced in an output winding changes depending on an angle of the rotor, and a position of the rotor can be found by reading the change. In addition, these conventional examples have a structure in which the number of turns of the output winding is the same in each tooth.
In these conventional examples, a rotation angle detection device having a small detecting position error and high accuracy is realized in an ideal case without a machining error. However, since a machining error actually occurs, a detecting position error may increase and desired accuracy may not be realized. For example, a detecting position error increases if roundness of an internal diameter of a rotor is deteriorated due to, for example, an error in arrangement of a winding or low accuracy of a mold used in punching out a core of the stator.
A rotation angle detection device with a shaft multiple angle of 2 is shown in FIG. 24 as a conventional example. More specifically, the conventional example of FIG. 24 corresponds to a rotation angle detection device in which the rotor described in JP 49-124508 A is formed to have two salient poles. In FIG. 24, reference numerals 100-1 and 100-2 denote two-phase output windings (hereinafter referred to as output winding (1) and output winding (2)). In addition, reference numeral 101 denotes teeth and 102 denotes a stator having eight teeth 101. Numerals 1 to 8 in the figure indicate teeth numbers. Reference numeral 103 denotes a rotor; 104, output windings with the number of turns N wound around the teeth 101; and 105, a rotation shaft of the rotor 103.
As shown in FIG. 24, the rotation angle detection device in this conventional example consists of the stator 102 having the eight teeth 101 and the rotor 103 having two salient poles and formed in a structure in which variation of permeance between the rotor and a gap surface pulsates and there is a double-crest pulsation component with a machine angle of 360 degrees. Although not shown in the figure, an excitation winding is concentrically wound around each tooth 101 on the stator 102 to have opposite polarities in the adjacent teeth 101. In addition, the two-phase output windings 100 is wound around the four teeth 101 (more specifically, the output winding (1) is wound around the teeth with the teeth numbers 1, 3, 5, and 7 and the output winding (2) are wound around the teeth with the teeth numbers 2, 4, 6 and 8) by the same number of turns N, respectively. However, polarities of the teeth are set to alternate. As shown in FIG. 24, the output winding (1) is wound around the teeth with the teeth numbers 1, 3, 5 and 7 such that polarities of the teeth alternate, that is, so as to have the same polarity in the teeth with the teeth numbers 1 and 5 and in the teeth with the teeth numbers 3 and 7 and have opposite polarities in the teeth with the teeth numbers 1 and 3. In addition, as shown in FIG. 24, the output winding (2) is wound around the teeth with the teeth numbers 2, 4, 6 and 8 such that polarities of the teeth alternate, that is, so as to have the same polarity in the teeth with the teeth numbers 2 and 6 and in the teeth with the teeth numbers 4 and 8 and have opposite polarities in the teeth with the teeth numbers 2 and 4. Further, these four windings 104 are connected in series. FIG. 25 shows the number of turns of the output winding in each tooth. In this way, in the conventional example shown in FIG. 24, the number of turns of the output winding is the same N in each tooth around which the output windings are wound. Then, a detecting position error is small and the rotation angle detection device operates as one with high accuracy in an ideal case without a machining error.
However, as already described, a detecting position error may increase and desired accuracy may not be realized because a machining error actually occurs. For example, a detecting position error may increase if roundness of an internal diameter of a stator deteriorates due to low accuracy of a mold used in punching out a core of the stator.
Increase in a detecting position error due to a machining error will be described citing a specific example. As an example, a case will be described in which a rotation angle detection device with an internal diameter of a stator of 20 mm and a shaft multiple angle of 2 is designed. Further, a winding specification is set to be the same as the aforementioned conventional example.
A case in which roundness of an internal diameter of a stator deteriorates and the internal diameter deforms into an elliptic shape will be considered. FIG. 31 shows detecting position errors in a case in which the internal diameter deforms deviating by 50 μm from a complete round shape and in an ideal state without a machining error and the shape of the internal diameter is a complete round. The horizontal axis indicates a position of a rotor in terms of a machine angle and the vertical axis indicates a detecting position error in terms of a machine angle. It is seen from this figure that a detecting position error increases as the internal diameter of the stator slightly deforms from a complete round shape. Moreover, it is also seen that a period of a detecting position error is a machine angle of 180 degrees, which is 360 degrees in terms of an electrical angle. However, an electrical angle is set to take a value obtained by multiplying a machine angle by a shaft multiple angle. In addition, a phase of this error with the period of the electrical angle of 360 degrees changes into various values depending on a machining error that has occurred.
Next, a case in which roundness of an internal diameter of a stator deteriorates and the internal diameter deforms into a square shape will be considered. FIG. 26 shows detecting position errors in a case in which the internal diameter deforms deviating by 20 μm from a complete round shape and in an ideal state without a machining error and the shape of the internal diameter is a complete round. The horizontal axis indicates a position of a rotor in terms of a machine angle and the vertical axis indicates a detecting position error in terms of a machine angle. It is seen from this figure that a detecting position error increases as the internal diameter of the stator slightly deforms from a complete round shape. Moreover, it is also seen that a period of a detecting position error is a machine angle of 90 degrees, which is 180 degrees in terms of an electrical angle. However, an electrical angle is set to take a value obtained by multiplying a machine angle by a shaft multiple angle. In addition, a phase of this error with the period of the electrical angle of 180 degrees changes into various values depending on a machining error that has occurred.
As described above, the conventional rotation angle detection device is designed to operate as a rotation angle detection device having a small detecting position error and high accuracy in an ideal case without a machining error. However, in reality, since a machining error inevitably occurs due to an error in arrangement of a winding, low accuracy of a mold used in punching out a core of the stator, or the like, a detecting position error may increase and desired accuracy may not be realized.