A kind of control method of low-speed direct driving type AC servo
Technical field
The present invention relates to the AC servo in a kind of industrial circle, especially a kind of for realizing the control method of low-speed direct driving type AC servo of high precision position control.
Background technology
AC servo is taking rare-earth permanent-magnet synchronous motor (PMSM) as driven object, AC servo is that manufacturing industry realizes automation and informationalized basic component, be used for relating to profile traces and follow the tracks of the technical field of controlling, its service behaviour under low cruise situation is one of most important performance.Conventional AC servo must be connected with mechanical load by reducing gear.Directly drive AC servo to be called for short direct-drive type AC servo, can not use reducing gear, drive with mechanical load direct-coupling, the benefit directly driving is apparent, owing to having saved transmission speed reducer structure, can realize higher control precision, faster response speed, higher efficiency, lower work noise etc.
Applied environment has very high requirement to the performance of direct drive AC servo, and the rotating speed while being mainly low cruise and torque performance require speed steady, and output torque approaches rated value.
Improve the low cruise performance of AC servo, thereby meet the requirement directly driving, can start with from two aspects, the firstth, rate accuracy and bandwidth while improving low cruise; The secondth, the impact of the non-linear factor such as dry friction dead band, mechanical clearance while overcoming low cruise.
In general AC servo, generally adopt increment photoelectric pulse coder as feedback element.Obtain the speed feedback information of motor from the output signal of increment photoelectric pulse coder, conventional speed-measuring method has M method, T method and M/T method at present.
It is the number m that records feedback pulse in the sampling period T setting that M method tests the speed
_{1}, the rotation speed n of obtaining thus motor is
$n=\frac{60{m}_{1}}{4\×{p}_{f}\×T}={K}_{\mathrm{\ω}}\×{m}_{1}---\left(1\right)$
In formula
P
_{f}---the resolution of photoelectric pulse coder, numeral 4 represents that photoelectric pulse coder output signal is through quadruple processing;
K
_{ω}---the speed feedback factor relevant with the sampling period with photoelectric pulse coder resolution.
Because feedback pulse is counted m
_{1}to be directly proportional to the rotating speed of motor, in the time of motor low cruise, the feedback pulse number m that can record within the sampling period
_{1}less, now M method rate accuracy is poor.
It is the cycle T by measuring photoelectric pulse coder output signal that T method tests the speed
_{f}calculate the rotating speed of motor, as long as meter is taken at a photoimpact cycle T
_{f}interior high-frequency impulse number m
_{2}, just can measure photoimpact cycle T
_{f}length, thereby record motor speed.Motor speed n is
$n=\frac{60f}{4\×{p}_{f}\×{m}_{2}}=\frac{{K}_{\mathrm{\ω}}}{{m}_{2}}---\left(2\right)$
In formula
The frequency of f---high-frequency impulse;
P
_{f}---the resolution of photoelectric pulse coder, numeral 4 represents that photoelectric pulse coder output signal is through quadruple processing;
K
_{ω}---the speed feedback factor relevant with high-frequency impulse frequency with photoelectric pulse coder resolution.
Due to rotating speed and the measured value m of motor
_{2}be inversely proportional to, the rotating speed of motor is higher, m
_{2}less, be applicable to measuring lower rotating speed therefore T method tests the speed, and precision is poor while measuring high rotating speed.And cycle T tests the speed
_{f}do not fix T when low speed
_{f}can be very large, the bandwidth that tests the speed is very low, is unfavorable for improving the control performance of servo system.
The time T d that tests the speed of M/T method forms by two sections, and first paragraph is fixing sampling period T0, and second segment is to finish from T0, to occurring first electro-optical feedback pulse during this period of time.While testing the speed by M/T method, motor speed n is
$n=\frac{60f\×{m}_{1}}{4\×{p}_{f}\×{m}_{2}}={K}_{\mathrm{\ω}}\×\frac{{m}_{1}}{{m}_{2}}---\left(3\right)$
In formula
M
_{1}---the time T that tests the speed d internal feedback umber of pulse;
M
_{2}---high-frequency impulse number in the time T that tests the speed d;
F---high-frequency impulse frequency;
K
_{ω}---the speed feedback factor relevant with high-frequency impulse frequency with the resolution of photoelectric pulse coder.
Although adopt M/T method to take into account the rate accuracy of high regime and low speed segment, also defectiveness, the time T that tests the speed d does not fix, and in the time that electromotor velocity is very low, the time T that tests the speed d may be still longer, and the bandwidth that tests the speed is lower.
Three kinds of methods all directly utilize the output signal of photoelectric pulse coder to detect AC servo motor speed above, in the time of servo AC servo motor low cruise, because the precision of common photoelectric pulse coder is limit, certainly lead to larger quantization error, thereby also affect velocity control accuracy, the stationarity variation of speed while showing low cruise, output torque obviously reduces, and does not all meet the requirement of direct-drive type AC servo.
Dry friction dead band and mechanical clearance etc. are ubiquitous non-linear factors in Mechatronic Systems, in the time that the slow-speed of revolution moves, the impact of these non-linear factors is especially obvious, if do not adopt suitable control method and compensatory device, these non-linear factors have a strong impact on runnability, even can cause phenomenons such as " creeping ".Owing to there is no reducing gear, direct-driving type AC servo general work, in lower-speed state, must be considered non-linear factor.
Summary of the invention
Object of the present invention, is to provide the control method of the low-speed direct driving type AC servo that a kind of control precision is high.
In order to reach above-mentioned purpose, solution of the present invention is:
A control method for low-speed direct driving type AC servo, comprises the steps:
Step 1: to the output current i of AC servo
_{a}, i
_{b}detect, and obtain quadrature axis current i by rotation transformation
_{q}with direct-axis current i
_{d}; Taking the corner measured value of AC servo motor as rotation transformation angle, obtaining of described corner measured value comprises the steps:
(11) on AC servo motor axle, photoelectric pulse coder is installed, and gather the output step-by-step counting of this photoelectric pulse coder, obtain the actual measurement angle signal θ (k) of k control cycle, k=1,2,3,, survey the reference signal of angle signal θ (k) as indirect operation using this;
(12) the indirect operation deviation of k control cycle of calculating
wherein,
represent the corner measured value of k control cycle;
(13) Δ θ (k) input torque compensating controller step (12) being obtained, obtains the compensated torque signal delta M (k) of k control cycle;
(14) calculate the estimated value of AC servo motor k control cycle output torque
wherein,
be the quadrature axis given value of current signal of k control cycle, K
_{t}for the moment coefficient of AC servo motor;
(15) Laplace transformation of the kinetic model of AC servo is
by the kinetic model discretization of AC servo, obtain the speed measured value of AC servo motor
with corner measured value
recursion formula:
$\hat{\mathrm{\ω}}(k+1)=(1-B\·\mathrm{\λ})\hat{\mathrm{\ω}}\left(k\right)+\mathrm{\λ}\·M\left(k\right)$
$\hat{\mathrm{\θ}}(k+1)=\hat{\mathrm{\θ}}\left(k\right)+\hat{\mathrm{\ω}}(k+1)\·\mathrm{\Δ}$
k=1,2,3,······
Wherein, s is laplace operator, and J is moment of inertia, and B is viscous friction coefficient, and Δ is the sampling period, λ=Δ/J;
Step 2: with corner measured value
for position feed back signal, by given angle position signal θ
^{*}with corner measured value
compare, obtain location following deviation, this location following deviation, through the adjusting computing of positioner, obtains speed preset signal ω
^{*};
Step 3: with speed preset signal ω
^{*}with aforementioned speed measured value
compare, obtain velocity deviation, this velocity deviation obtains aforementioned quadrature axis given value of current signal through the adjusting computing of speed control
Step 4: by quadrature axis given value of current signal
with aforementioned quadrature axis current i
_{q}compare, obtain quadrature axis current deviation, this quadrature axis current deviation, through the adjusting computing of quadrature axis current controller, obtains quadrature-axis voltage u
_{q};
Step 5: setting the given signal of direct-axis current is 0, by given this direct-axis current signal and aforementioned direct-axis current i
_{d}compare, obtain direct-axis current deviation, this direct-axis current deviation, through the adjusting computing of direct-axis current controller, obtains direct-axis voltage u
_{d};
Step 6: with corner measured value
for the anglec of rotation, to aforementioned quadrature-axis voltage u
_{q}with direct-axis voltage u
_{d}carry out reverse rotation conversion, obtain three-phase alternating current pressure reference signal u
_{a}, u
_{b}, u
_{c}, then to aforementioned three-phase alternating current pressure reference signal u
_{a}, u
_{b}, u
_{c}carry out space vector pulse width modulation, the pulse-width signal obtaining, for control inverter, drives AC servo motor.
Further, in described step 4, also by torque dither signal
with quadrature axis given value of current signal
superimposed; Described torque dither signal
obtain as follows: by the speed preset signal ω in abovementioned steps two
^{*}through window function processing, obtain dither amplitude control signal, aforementioned dither amplitude control signal and given oscillator signal multiply each other, and obtain torque dither signal
According to such scheme, the present invention adopts corner measured value and speed measured value to detect corner and the rotating speed of AC servo motor, has improved corresponding accuracy of detection, particularly accuracy of detection when low speed.Also utilize torque dither signal, realize the torque shake of AC servo motor in the time of zero-speed, overcome the impact of dry friction on servo system low cruise performance, control performance is improved.
Brief description of the drawings
Fig. 1 is schematic diagram of the present invention.
Fig. 2 is the dynamic structure figure of corner in Fig. 1, the indirect measurement links of rotating speed.
Fig. 3 is the theory diagram of zero-speed torque shake in Fig. 1.
Fig. 4 is the main flow chart of control method of the present invention.
Fig. 5 is Interruption flow chart of the present invention.
Fig. 6 realizes part circuit structure figure of the present invention.
Specific embodiments
Below with reference to accompanying drawing, technical scheme of the present invention is elaborated.
The invention provides a kind of control method of low-speed direct driving type AC servo, control principle as shown in Figure 1.Position closed loop, speed closed loop, q shaft current closed loop and d shaft current closed loop are comprised.To the output current i of low-speed direct driving type AC servo
_{a}, i
_{b}detect, and obtain quadrature axis current i by rotation transformation
_{q}with direct-axis current i
_{d}, be respectively used to q shaft current closed loop feedback and d shaft current closed loop feedback.
Described rotation transformation angle is real is the corner of AC servo motor rotor, and this corner obtains by indirect operation in the present invention.When adopting direct-axis current i
_{d}when=0 control strategy, quadrature axis current i
_{q}be directly proportional to the electromagnetic torque of low-speed direct driving type AC servo, and quadrature axis given value of current signal in low-speed direct driving type AC servo
can obtain in real time, based on this, as long as speed and angle position etc. that the mathematical reconfiguration of realizing kinetic model to AC servo motor and quadrature axis current diffusion limited model just can indirect operation AC servo motor, claim that hereinafter adopting the link of this method observation AC servo motor corner and rotating speed is " corner, the indirect measurement links of rotating speed ", this link as shown in Figure 2.
The concrete steps that obtain corner measured value and speed measured value are as follows:
Step 1: on AC servo motor axle, photoelectric pulse coder is installed, and gather the output step-by-step counting of this photoelectric pulse coder, obtain the actual measurement angle signal θ (k) of k control cycle, k=1,2,3,, survey the reference signal of angle signal θ (k) as indirect operation using this;
Step 2: the indirect operation deviation of calculating k control cycle
wherein,
represent the corner measured value of k control cycle;
Step 3: Δ θ (k) the input torque compensating controller that step 2 is obtained, obtains the compensated torque signal delta M (k) of k control cycle;
Step 4: calculate the estimated value of AC servo motor k control cycle output torque
wherein,
be the quadrature axis given value of current signal of k control cycle, K
_{t}for the moment coefficient of AC servo motor;
Step 5: the Laplace transformation of the kinetic model of AC servo is
by the kinetic model discretization of AC servo, obtain the speed measured value of AC servo motor
with corner measured value
recursion formula:
$\hat{\mathrm{\ω}}(k+1)=(1-B\·\mathrm{\λ})\hat{\mathrm{\ω}}\left(k\right)+\mathrm{\λ}\·M\left(k\right)$
$\hat{\mathrm{\θ}}(k+1)=\hat{\mathrm{\θ}}\left(k\right)+\hat{\mathrm{\ω}}(k+1)\·\mathrm{\Δ}$
k=1,2,3,······
Wherein, s is laplace operator, and J is moment of inertia, and B is viscous friction coefficient, and Δ is the sampling period, λ=Δ/J.
Generally, the electric current loop of AC servo all has enough bandwidth, therefore only having moment of inertia J and viscous friction coefficient B is the system parameters that affects corner, the indirect measurement links of rotating speed, between the parameter value using and real system parameter, can there is certain error in corner, the indirect measurement links of rotating speed, may cause the skew between measured value and actual value, must compensate by compensated torque control signal.By the output step-by-step counting to photoelectric pulse coder, can obtain the reference signal θ (k) of AC servo motor corner, by the reference signal θ of corner (k) with outer corner measurement value be
compare, can obtain corner observed deviation
observed deviation Δ θ (k), through the calculating of compensated torque controller, can obtain compensated torque signal delta M, compensated torque controller adoption rate integral algorithm, and compensation is controlled parameter and is comprised proportionality coefficient and integral coefficient.
The corner measured value that indirect operation obtains
can be respectively used to rotation transformation, reverse rotation conversion and angle position feedback, speed measured value
can be used for speed feedback.
With the given signal θ of angle position
^{*}with corner measured value
compare, obtain location following deviation, this location following deviation, through the adjusting computing of positioner, can obtain speed preset signal ω
^{*}.
With speed preset signal ω
^{*}with aforementioned speed measured value
compare, can obtain velocity deviation, this velocity deviation can obtain quadrature axis given value of current signal through the adjusting computing of speed control
With quadrature axis given value of current signal
with aforementioned by detecting and convert the quadrature axis current i obtaining
_{q}compare, can obtain quadrature axis current deviation, this deviation, through the adjusting computing of quadrature axis current controller, can obtain quadrature-axis voltage u
_{q}.
The given value of current signal of setting d-axis is 0, by this given value of current signal and aforementioned by detecting and convert the direct-axis current i obtaining
_{d}compare, obtain direct-axis current deviation, this deviation, through the adjusting computing of direct-axis current controller, obtains direct-axis voltage u
_{d}.
According to the aforementioned corner measured value obtaining
to aforementioned quadrature-axis voltage u
_{q}with direct-axis voltage u
_{d}carry out reverse rotation conversion, obtain three-phase alternating current pressure reference signal u
_{a}, u
_{b}, u
_{c}, then to aforementioned three-phase alternating current pressure reference signal u
_{a}, u
_{b}, u
_{c}carry out space vector pulse width modulation, the pulse-width signal obtaining, for control inverter, drives AC servo AC servo motor.
In low-speed direct driving type AC servo, inevitably can there is frictional resistance.Frictional resistance can be divided into viscous friction drag and dry friction resistance, viscous friction drag and speed are directly proportional, and dry friction resistance is substantially irrelevant with the size of speed, to low-speed direct driving type AC servo influence on system operation maximum is dry friction resistance, especially in the time of low cruise, dry friction resistance can cause speed dead band, sometimes even can cause system oscillation.In direct-driving type AC servo, be necessary dry friction resistance to compensate, to meet the requirement of directly driving.The concrete way that the present invention adopts is the high frequency torque dither signal that adds little amplitude
by itself and quadrature axis given value of current signal
superimposed, thus make AC servo motor low speed or when static in " micro-shake " state, to realize " electric lubricated ", can effectively improve like this dead band and the hysteresis characteristic of low-speed direct driving type AC servo.The frequency of " micro-shake " should be away from the natural resonance point of low-speed direct driving type AC servo, and oscillation amplitude is less than drive gap.In technical scheme provided by the invention, make low-speed direct driving type AC servo that " micro-shake " occur under static and lower-speed state by " zero-speed torque shake link ".
Described torque dither signal
obtain as follows: as shown in Figure 3, by aforementioned speed preset signal ω
^{*}through window function processing, obtain dither amplitude control signal, aforementioned dither amplitude control signal and given oscillator signal multiply each other, and obtain torque dither signal
torque dither signal
amplitude speed increase and reduce.
It is processor that low-speed direct driving type AC servo of the present invention adopts TMS320F28035, the modules such as the corner in Fig. 1, the indirect measurement links of speed, positioner PT, speed control ST, d shaft current controller LD, q shaft current controller LQ, zero-speed torque shake link, rotation transformation, reverse rotation conversion realize by software, and space vector pulse width modulation (SVPWM) is realized by the hardware of TMS320F28035 inside.As shown in Figure 6, adopt two current sensor ACS712 to detect AC servo motor stator current i
_{a}, i
_{b}, the signal of current sensor is input to the A/D translation interface of TMS320F28035.Major loop is hand over-straight-knot structure, and inverter is wherein realized by Intelligent Power Module IRAMX20UP60A.
As shown in Figure 4, the main flow of low-speed direct driving type AC servo control method of the present invention is as follows: 1) initialization system clock, interrupt vector table, IO port, 2) initialization control parameter list, 3) initialization A/D change-over circuit, SVPWM output, 4) start control cycle timer, 5) wait for that control cycle timer interrupts, refreshes man-machine interface, 6) according to current i
_{a}, i
_{b}, i
_{c}currency, calculate i
_{q}and i (k)
_{d}(k), 7) read photoelectric encoder feedback signal theta (k), 8 by eQEP interface) calculating indirect operation deviation calculating indirect operation deviation
9) computational load compensated torque value; 10) calculate corner measured value and speed measured value, 11) respectively with 1 times, 2 times, the 4 times control cycles in major cycle cycle, completing place controller, speed control, current controller refresh computing; 12) according to the output signal u of cross, straight shaft current controller
_{q}and u (k)
_{d}, and corner measured value (k)
convert by reverse rotation, calculate the reference value of Three-phase electronic voltage, refresh SVPWM link.
As shown in Figure 5, the timer break in service flow process of low-speed direct driving type AC servo control method is as follows: 1) response Interruption, 2) start A/D converter, 3) read A phase current sampling value, 4) read B phase current sampling value, 5) interrupt returning.
The present invention only needs to adopt common AC servo motor and conventional increment photoelectric pulse coder, by improving, has improved AC Servo System Low Speed runnability, has met the requirement of direct driving.
The present invention adopts corner measured value and speed measured value to detect corner and the rotating speed of AC servo motor, has improved corresponding accuracy of detection, particularly accuracy of detection when low speed.Also utilize torque dither signal, realize the torque shake of AC servo motor in the time of zero-speed, overcome the impact of dry friction on servo system low cruise performance, control performance is improved.
Above embodiment only, for explanation technological thought of the present invention, can not limit protection scope of the present invention with this, every technological thought proposing according to the present invention, and any change of doing on technical scheme basis, within all falling into protection range of the present invention.