1. Field of the Invention
The present invention relates to a rotary detector which can reduce the torque ripple of a rotor and the like by reducing the ripple component of an output signal.
2. Description of the Related Art
The output torque of a motor generally contains ripples. Since torque ripples are caused by speed irregularities and positional displacement of the support motor, they adversely affect the processing precision in, for example, an NC (numerical control) apparatus, and spoil the smoothness of an elevator ride by increasing carriage shaking.
When detecting this type of torque ripple, the torque ripple may be internal, arising in the motor main body comprising an accelerator, or external, arising in a rotary detecting sensor. Internal torque arises from the work precision of a motor stator and a rotor, eccentricity of the rotor bearing, a high-frequency magnetic field inside the motor, and the assembly precision of the decelerator. Many conventional methods have been proposed for reducing torque ripples of the former type. For example, Japanese Patent Application No. 7-129251 centers on the torque ripple generated by a decelerator, and calculates a correction signal Tcomp (=A·sin (θ+á1) where A is the torque ripple adjustment gain, θ is the angle of rotation of the decelerator, and á1 is the initial phase; in synchronism with the rotation cycle of the motor, this signal is fed forward and added to the target torque command, thereby canceling the torque ripple. Japanese Patent Application No. 11-299277 proposes storing the correlation between the torque ripple and the angle of rotation of the motor in a memory apparatus, reading a torque ripple corresponding to the angle of rotation of the motor, and creating a new torque command value by subtracting the ripple portion from the torque command value.
Since torque ripples of the latter type in the rotation detecting sensor mentioned above appear as motor torque ripples, the ripple problem can usually be reduced by applying a control method, such as the one described above, in the apparatus which controls the motor. However, when the ripples are caused by the angle of rotation being detected in the output value of the rotation detecting sensor, the amplitude of the ripples becomes larger in proportion to the detected angle speed, leading to a problem that it becomes impossible to increase the angle speed feedback gain when controlling the torque of the motor and the rotation speed; this places an enormous burden on the control apparatus and increases the cost of the apparatus.
In this way, a variety of control methods have been applied in the controller and driver of the rotating machine in conventional rotary detectors, in an attempt to ensure that a ripple in the output does not become a torque ripple and speed irregularities of the rotating machine which the rotary detector is installed in. For this reason, the controller and driver of the rotating machine become complex, lowering its reliability and increasing the cost. Furthermore, in addition to ripples in the output of the rotary detector, torque ripples in an electric motor include those generated by assembly precision of the decelerator, processing precision of the motor main body, high-frequency magnetic fields and the like, making it difficult to determine the cause of the ripples in the output of the rotary detector, and undermining its performance as a sensor.
The present invention has been realized based on the circumstances described above, and aims to provide a rotary detector which can reduce output ripples, eliminate torque ripples and speed irregularities of an actuator, such as a rotating machine, which the rotary detector is installed in, simplify the driver and controller of the actuator, reduce costs, and increase reliability.
In order to achieve the above objects, the rotary detector according to a first aspect of this invention comprises a rotary detector unit which detects rotary motion of a rotor; and a rotary calculator unit comprising a rotation angle detector, which detects the rotation angle of the rotor, and an angle speed detector which detects the angle speed of the rotor, based on the output of the rotary detector unit. The rotary calculator unit comprises a trigonometrical calculator which calculates a sine value or a cosine value of the rotation angle detected by the rotary detector; a gain adjuster which multiplies the sine value or the cosine value, calculated by the trigonometrical calculator, by a predetermined gain; a multiplier which multiplies the output of the gain adjuster by the output of the angle speed detector; and a subtracter which subtracts the output of the multiplier from the output of the angle speed detector.
According to a second aspect of the invention, in the rotary detector of the first aspect, the trigonometrical calculator comprises a phase adjuster which adjusts the phase of the rotation angle, detected by the rotation angle detector.
According to a third aspect of the invention, in the rotary detector of the first aspect, the rotary detector unit comprises a resolver which creates an output in accordance with the rotation angle of the rotor.
According to a fourth aspect of the invention, in the rotary detector of the first aspect, the rotary detector unit comprises a generator which outputs a voltage in accordance with the angle speed of the rotor.
According to a fifth aspect of the invention, in the rotary detector of the first aspect, the rotary detector unit comprises an encoder which creates an output in accordance with the rotation angle of the rotor.
According to a sixth aspect of the invention, in the rotary detector of the first aspect, the rotary detector unit is provided separate from the rotary calculator unit.
According to a seventh aspect of the invention, in the rotary detector of the first aspect, the rotary detector unit houses the rotary calculator unit.
According to an eighth aspect of the invention, in the rotary detector of the first aspect, the rotary calculator unit comprises a unit for reducing a ripple component of the angle speed.
According to a ninth aspect of the invention, in the rotary detector of the first aspect, the rotary calculator unit calculates an angle speed ωout by calculatingωout=ω(1−G·sin (nθ+Ψ)                where θ represents the rotation angle, G represents the gain of the gain adjuster, Ψ represents the adjust phase value of the phase adjuster, and n represents the number of ripple cycles in the output of the rotary angle detector in one rotation of the rotor.        
According to a tenth aspect of the invention, in the rotary detector of the first aspect, the rotary calculator unit comprises a unit for reducing a ripple component of the rotation angle.
According to an eleventh aspect of the invention, in the rotary detector of the first aspect, the rotation angle detector comprises an integrator which obtains a rotation angle by integrating the output of the angle speed detector.
According to a twelfth aspect of the invention, in the rotary detector of the first aspect, the rotary calculator unit comprises an integrator for integrating the angle speed output ωout.
According to a thirteenth aspect of the invention, in the rotary detector of the first aspect, the rotary calculator unit outputs a rotation angle signal which reduces the ripple component of the rotation angle, and an angle speed signal which reduces the ripple component of the angle speed.
According to a fourteenth aspect of the invention, in the rotary detector of the first aspect, the rotary calculator unit is provided in series in a plurality of levels.
According to a fifteenth aspect of the invention, in the rotary detector of the second aspect, the phase adjuster has a plurality of adjust phase values, and selectively outputs one of the plurality of adjust phase values in accordance with a direction of the torque acting on the rotor.
According to a sixteenth aspect of the invention, in the rotary detector of the first aspect, the gain adjuster varies the predetermined gain in accordance with external power in the gravitational direction acting on the rotor rotation axis of the rotor.
Principles
This invention can effectively eliminate the ripple component in the output of a rotary detector unit, and particularly the ripple component which is dependent on the rotation cycle of the device being measured. When the output of the rotary detector unit contains a plurality of ripple components, all the ripple components can effectively be eliminated by provided a plurality of rotary calculators in correspondence with the ripples. That is, when θo represents the rotation angle of the device being detected, the output of a rotary detector unit having a ripple with an amplitude of a is converted by a rotation angle detector to the rotation angle output θ of the following equation.θ=θo−a·cos(nθo+φ)  (2)                where n represents the number of ripple cycles in one rotation of the device being detected, and φ represents the initial phase difference when attaching the rotary detector unit to the device being detected.        
In the present invention, for example, when an angle speed detector time-differentiates the rotation angle output θ, the following angle speed output ω is obtained.ω=dθo/dt(1+a·n·sin(nθo+φ))  (3)
When a rotary calculator unit calculates the output ωout of the unit based, for example, on equation (1), the output ωout is expressed by substituting equations (2) and (3) for equation (1) as follows
                              ω          out                =                              ⅆ                          θ              o                                /                      ⅆ                          t              ⁡                              (                                  1                  -                                      G                    ·                                          sin                      ⁡                                              (                                                  Ψ                          -                                                      a                            ·                            n                            ·                                                          cos                              ⁡                                                              (                                                                                                      n                                    ⁢                                                                                                                                                  ⁢                                                                          θ                                      o                                                                                                        +                                  ϕ                                                                )                                                                                                              +                                                      n                            ⁢                                                                                                                  ⁢                                                          θ                              o                                                                                                      )                                                                              +                                      a                    ·                    n                    ·                                          sin                      ⁡                                              (                                                                              n                            ⁢                                                                                                                  ⁢                                                          θ                              o                                                                                +                          ϕ                                                )                                                                              -                                                            a                      ·                      n                      ·                      G                      ·                                              sin                        ⁡                                                  (                                                      Ψ                            -                                                          a                              ·                              n                              ·                                                              cos                                ⁡                                                                  (                                                                                                            n                                      ⁢                                                                                                                                                          ⁢                                                                              θ                                        o                                                                                                              +                                    ϕ                                                                    )                                                                                                                      +                                                          n                              ⁢                                                                                                                          ⁢                                                              θ                                o                                                                                                              )                                                                                      ⁢                                          sin                      ⁡                                              (                                                                              n                            ⁢                                                                                                                  ⁢                                                          θ                              o                                                                                +                          ϕ                                                )                                                                                            )                                                                        (        4        )            Here, dθo/dt represents the angle speed of the device being detected.
In equation (4), since the ripple amplitude is generally small so that a <<1, when a trigonometrical function is developed in a near-linear form near an angle of zero, the equation becomes
                                                        ω              out                        =                                          ⅆ                                                                  ⁢                                  θ                  0                                            /                              ⅆ                                  t                  ⁡                                      (                                          1                      -                                              G                        ·                                                  sin                          ⁡                                                      (                                                          Ψ                              +                                                              n                                ⁢                                                                                                                                  ⁢                                                                  θ                                  o                                                                                                                      )                                                                                              +                                                                        a                          ·                          n                          ·                          G                          ·                                                      cos                            ⁡                                                          (                                                              Ψ                                +                                                                  n                                  ⁢                                                                                                                                          ⁢                                                                      θ                                    o                                                                                                                              )                                                                                                      ⁢                                                  cos                          ⁡                                                      (                                                                                          n                                ⁢                                                                                                                                  ⁢                                                                  θ                                  o                                                                                            +                              ϕ                                                        )                                                                                              +                                              a                        ·                        n                        ·                                                  sin                          ⁡                                                      (                                                                                          n                                ⁢                                                                                                                                  ⁢                                                                  θ                                  o                                                                                            +                              ϕ                                                        )                                                                                              -                                                                        a                          ·                          n                          ·                          G                          ·                                                      sin                            ⁡                                                          (                                                              Ψ                                -                                                                  a                                  ·                                  n                                  ·                                                                      cos                                    ⁡                                                                          (                                                                                                                        n                                          ⁢                                                                                                                                                                          ⁢                                                                                      θ                                            o                                                                                                                          +                                        ϕ                                                                            )                                                                                                                                      +                                                                  n                                  ⁢                                                                                                                                          ⁢                                                                      θ                                    o                                                                                                                              )                                                                                                      ⁢                                                  sin                          ⁡                                                      (                                                                                          n                                ⁢                                                                                                                                  ⁢                                                                  θ                                  o                                                                                            +                              ϕ                                                        )                                                                                                                )                                                                                ⁢                                          ⁢                                                    Assuming                ⁢                                                                  ⁢                                  a                  ·                  G                                            =              0                        ,            then                          ⁢                                                      (        5        )                                          ω          out                =                              ⅆ                          θ              o                                /                      ⅆ                          t              ⁡                              (                                  1                  -                                      G                    ·                                          sin                      ⁡                                              (                                                                              n                            ⁢                                                                                                                  ⁢                                                          θ                              o                                                                                +                          Ψ                                                )                                                                              +                                      a                    ·                    n                    ·                                          sin                      ⁡                                              (                                                                              n                            ⁢                                                                                                                  ⁢                                                          θ                              o                                                                                +                          ϕ                                                )                                                                                            )                                                                        (        6        )            Equation (6) shows that, when the gain G of in equation (1) can be set equal to the proportion of ripples a·n, and the adjust phase Ψ can be set equal to the initial phase difference φ, the output ωout of the rotary calculator unit is equal to the angle speed dθo/dt of the detected device, and the ripple component in the output of the rotation angle detector unit can be eliminated.
Furthermore, error between the output ωout of the rotary calculator unit and the angle speed dθo/dt can be determined from Equation (6) as
                              e          rr                =                              ω            -                                          ⅆ                                  θ                  o                                            /                              ⅆ                t                                              =                                    (                                                a                  ·                  n                  ·                                      sin                    ⁡                                          (                                                                        n                          ⁢                                                                                                          ⁢                                                      θ                            o                                                                          +                        ϕ                                            )                                                                      -                                  G                  ·                                      sin                    ⁡                                          (                                                                        n                          ⁢                                                                                                          ⁢                                                      θ                            o                                                                          +                        Ψ                                            )                                                                                  )                        ⁢                                          ⅆ                                  θ                  o                                            /                              ⅆ                t                                                                        (        7        )            which can be expanded to
                              e          rr                =                                            ⅆ                              θ                o                                      /                          ⅆ              t                                ⁢                                    (                                                                    a                    2                                    ⁢                                      n                    2                                                  +                                  G                  2                                -                                  2                  ⁢                                                                          ⁢                  anG                  ⁢                                                                          ⁢                                      cos                    ⁡                                          (                                              ψ                        -                        ϕ                                            )                                                                                  )                                ×                      sin            ⁡                          (                                                n                  ⁢                                                                          ⁢                                      θ                    o                                                  +                ϕ                -                                                      tan                                          -                      1                                                        ⁢                                                            G                      ⁢                                                                                          ⁢                                              sin                        ⁡                                                  (                                                      ψ                            -                            ϕ                                                    )                                                                                                            an                      -                                              G                        ⁢                                                                                                  ⁢                                                  cos                          ⁡                                                      (                                                          ψ                              -                              ϕ                                                        )                                                                                                                                                          )                                                          (        8        )            
The amplitude of the error err is a concave function having its only minimum point at zero with respect to, for example, a gain G of between 0 to 2 an, and an adjust phase Ψ of between −π+φ+ to π+φ+; the minimum value of zero can easily be determined from appropriate values for G and Ψ. When the proportion of ripples an and the initial phase φ are known in advance, G and Ψ should of course be set to their known values from the start.
In this way, the present invention is able to reduce the output ripples of a rotary detector, and can also reduce torque ripples and speed irregularities in an actuator such as a rotor, which the rotary detector is installed in. Further, since the output ripple can be determined by the simple computation of Equation (1), the drive device and control device for the actuator can be simplified and cost can be lowered. As is clear from Equation (8), when the amplitude of the error err is zero, the ripple component can be reduced irrespective of the rotation speed of the detected device, increasing the precision and reliability of the rotary detector.