Most of us know the robots in science fiction, but the reality of the increasing number of real is a machine that can guide and remote boot itself. These robots operating planning in advance good specific tasks, such as assembly line work, surgical assistance, warehouse delivery/retrieval, and even dangerous tasks such as mine. Now robots can not only deal with high degree of repetition of work, also can finish on the direction and demand flexibility of complex function.
figure 1: now the robot is widely used in small areas such as SMT machine, install machines in large areas, such as the automatic assembly line, they are on the assembly line service, placement, installation and welding and assembling parts
the implementation of these high-performance machines thanks to the promotion of the following several aspects: one is to help them & other; Listen & throughout; 、“ See & throughout; 、“ Feeling & throughout; The ascent of the sensor; 2 it is to realize real-time decision making ability and the complexity of algorithm and the calculation of the action; Three is to use speed, accuracy, and the ascension of the motor mechanical power to implement these decisions. Each of these aspects have played an important role in robot design, because the technology progress and the synergy between them are established quickly in itself.
the traditional sense, motor control has always been a difficult problem for electronic engineer, because want to consider a number of key issues and we are quite different in common electronic encountered. Fortunately, due to the improvement of technology, make easier to understand and deal with these problems, but also make high-performance performance possible. TI company DRV8816 double half bridge, for example, motor drives have been integrated including short protection, high temperature alarm, such as high power internal protection function. Low power sleep mode off the internal circuit, in order to achieve very low static current. Highly integrated controller and reflects the electronic and motor drive in terms of flexibility and integration of hierarchies. Motor choose
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when choose the specific motor model, there are three primary factors of designers to consider:
1. The minimum maximum speed motor (And acceleration)
2. Motor can provide the maximum torque, and the relationship between torque and speed curve
3. Motor operation (No sensors and closed loop control)The accuracy and repeatability of
of course, when choosing motor and many others, such as size, weight and cost, and other important factors to consider. Almost for all small to medium sized robot drive, the choice of drive motor usually have the brushless dc motor, brushless dc motor (刷)。
brush motor, the technology, the oldest of the dc motor is the most simple, the cost is the lowest choice (FIG. 2)。 Due to the contact between the current-carrying brush and the rotor, the rotation of the motor rotor will switch (Steering)Field around the rotor winding. The speed of the motor is a function of the applied voltage, and thus drive request is not high, but the management of torque and associated position is difficult. Due to the motor wear, because of the brush and spring is dirty need cleaning, and since the brush and the rotor contact sparks may become the electronic noise sources (The electromagnetic interference)Factors, such as driving conditions and reliability problems. As a result of the existence of these problems, in most cases, a brush motor for robot design is the least attractive option.
figure 2: brush in the brush motor, conductive (With copper brush or more likely to be produced by graphite blocks)Contact with the rotor on the contact. As the rotor turn, it will switch the coil current polarity
brushless motor (Figure 3)Began in the 1860 s, thanks to the development of two aspects: one is the strong permanent magnets, small size, low cost; The second is the small size of high efficiency electronic switch (Usually the MOS tube, but sometimes is a bipolar transistor) with low pressure dropTo switch to the winding current. Switch around fixed coil with the rotation of the interaction between the magnets on the core replaced with the mechanical commutator brush motor. Through the accurate control MOS tube (Are usually configured in H bridge structure)On and off, switch on the coil magnetic field was. By changing the MOS tube on-off frequency, motor speed which can be controlled. In addition, through a sensor, motor controller can get to the position of the robot, it can have a better control on the performance of the robot.
figure 3: in the brushless motor, when the interaction with the permanent magnet on the rotor coil magnetic field, coil current in the stator winding is the electric switch. Diagram, vacancy of rotor belong to the middle position
