Sewing Machine Electric Motor Start mode
A. A new method for start At present, the PID parameter installation method research is domestic, like phase angle allowance installation algorithm, neural network PID algorithm, as well as heredity optimization PID algorithm and so on. These methods may enable the system performance to have the improvement, but design process complex tedious, the practical application is restricted. In fact the PI controller is widely used in control system because its structure simple, and it is easy to realize, the reliability to be high. However, there are contradictory in the rapidity and the over target by using PI control policy  . Uses the pulse width velocity modulation, when PWM is changed, the control voltage is changed, the converter outputs the average voltage according to the linear rule change, but its response is late. Therefore the PWM system may also regard as is a delay component, so the velocity of the motor and starting time is control hardly. This paper uses three steps that the control voltage is changed by different control’s mode . The starting time can be changed in the second step.
B. First step P control In the first step, the acceleration period may carry on the open-loop control, causes the motor slow start by constant acceleration. When arrives at the preinstall definite value, entered the stable velocity modulation stage. The value of PWM is changed in the proportionate mode before the brushless direct current motor rotating, which time is short. d = k *d0 (2) Which d is the data of PWM register, k is proportion, d 0 is the register’s first data that be given by the system. The first step control mode is over when motor starts to rotate. The velocity of motor is slow during P control mode. The velocity of motor can be changed from zero to the motor start to rotate. The other installments of sewing machine can be protected during the first step . If k is small, then the starting time value is small, and if k is big, the starting time value is big.
C. Second step PI control In order to reduce the over modulation, firstly, reduces the PWM value, which the PWM value is equal to d-d*5%. Secondly, according to the brushless direct current motor’s start and the velocity modulation characteristic, this article uses PI control method during the second step period. For the PWM value is changed fast, and the motor velocity changes slowly, as well as obtains the velocity is slow than the PWM value. The proportion value is small, and the PWM value is changed slowly when the obtained velocity is close to the given velocity.
D. Three step PID control In order to obtain the good velocity modulation performance, usually must construct a closed-loop system. We use PID mode to control motor when the obtained velocity is very close to the given velocity. A second-order linear controller through the adjustment proportion, the integral and the differential three parameters, causes the majority industrial control system to obtain the good closedloop control performance. The basic PID controller’s ideal mathematical formula is (3), = + + t d i p dt det e t dt T T u t K e t 0 ( ) ( ) 1 ( ) ( ) (3) The u(t)is controller’s output, e(t) is controller’s input K p is controller’s proportion magnification factor, Ti is controller’s integration time, Td is controller’s rate time. Supposes u(k) is the controller’s value during the sampling time, we can obtain result in the separate the PID mathematical formula (3), ( ) ( ) ( ) [ ] ( ) ( 1) 0 = + + − − = u k K e k K e j K e k e k d k j p i (4) i p i T K T K = (5) T K T K p d d = (6) Δu(k)=K Δe(k)+Ke(k)+K [ ] Δe(k)−Δe(k−1) p i d (7) Therefore, so long as Kp ,Ti and Td is determined, use the deviation amount which several times survey to be possible to extract the control increase   . In this paper, Δu(k) is small during the third step period, which Δu(k) is the PWM value.
Take LPC2292 Central Processing Unit as its control system key part of DC motor, adopts other designs both of hardware and software, completed a suit of driving system. The LPC2292 micro controllers are based on a 16/32-bit ARM7TDMI-S CPU with real-time emulation and embedded trace support, together with 256 KB of embedded high-speed flash memory. A 128-bit wide memory interface and the unique accelerator architecture enable 32-bit code execution at the maximum clock rate. The alternative 16-bit Thumb mode reduces code by more than 30 % with minimal performance penalty .
In the experiment discovered when receives the strong electromagnetic interference, in view of ARM system CPU characteristic, on the one hand establishes watch-dog register, the system automatic reset microprocessor. On the other hand, changes undefined instruction the revision to cause CPU to enter time the normal state. Because the load is different, the system’s response is different. The starting time is different by using other control mode. In order to realize the starting time is same in different load with sewing system, which the load is small when the sewing machine is not sewing the cotton material, if the machine is sewing, then the load is big. Adopts the three steps control mode, the system can change PWM value according to different load. The result indicated that the system response speed is quick, the stability good, does not have the over modulation basically. The brushless direct current motor’s stable state situation meets the design requirements.