Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
ActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)tors)•AC motors (induction motors and synchronous motors)•Linear actuators•Hydraulic and pneumatic actuators•Modeling and analysis of actuators•Practical performance and parameters of actuators•Sizing and selection of actuators for practical applications•Instrumentation, drive hardware, and control Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)of actuators7.1IntroductionThis chapter introduces the subject of actuators, as related to mechatronics. The actuator is the device that mechanicallyClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
drives a mechatronic system. Joint motors in a robotic manipulator are good examples of such actuators. Actuators may be used as well to operate contrActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)atically use response error signals from a process in feedback to correct the operation of the process (i.e., to drive the process to achieve a desired response) are termed servoactuators. In particular, the motors that use measurements of position, speed, and perhaps load torque and armature curren Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)t or field current in feedback to drive a load to realize a specified motion are termed servomotors.One broad classification separates actuators intoClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
two types: incremental-drive actuators and continuous-drive actuators. Stepper motors, which are driven in fixed angular steps, represent the class ofActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)igital actuator causes the actuator to move by a predetermined, fixed increment of displacement. Continuous-drive devices are very popular in mechatronic applications. Examples are direct current (de) torque motors, induction motors, hydraulic and pneumatic motors, and piston-cylinder drives (rams). Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2) Microactuators are actuators that are able to generate very small (microscale) actuating forces/torques and motions. In general, they can be neither4Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
65466Mechatronics: A Foundation Coursedeveloped nor analyzed as scaled-down versions of regular actuators. Separate and more innovative procedures of ActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)modern information storage systems. Distributed or multilayer actuators constructed using piezoelectric, electrostrictive, magnetostrictive, or photostrictive materials are used in advanced and complex applications such as adaptive structures. An actuator may be directly connected to the driven load Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2) and this is known as the “direct-drive" arrangement. More commonly, however, a transmission device may be needed to convert the actuator motion intoClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
a desired load motion for the proper matching of the actuator with the driven load. The stepper motor, de motor, alternating current (ac) induction moActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)ussed and the procedures of actuator selection are also addressed.7.2Stepper MotorsStepper motors are a popular type of actuator. They are driven in fixed angular steps (increments). Each step of rotation is the response of the motor rotor to an input pulse (or a digital command). In this manner, th Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)e stepwise rotation of the rotor can be synchronized with pulses in a command-pulse train, assuming of course that no steps are missed, thereby makingClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
the motor respond faithfully to the input signal (pulse sequence) in an open-loop manner. Like a conventional continuous-drive motor, a stepper motorActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)otor, stepping motor, and step motor are synonymous and are often used interchangeably.One common feature in any stepper motor is that the stator of the motor contains several pairs of field windings (or phase windings) that can be switched on to produce electromagnetic pole pairs (N and S). These p Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)ole pairs effectively pull the motor rotor in sequence so as to generate the torque for motor rotation. By switching the currents in the phases in anClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
appropriate sequence, either a clockwise (CVV) rotation or a counterclockwise (CCVV) rotation can be produced. The polarities of a stator pole may havActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2) for a phase winding could be supplied by a microprocessor or a personal computer (a software approach), it is customary to generate it through hardware logic in a device called a translator or an indexer. This approach is more effective because the switching logic for a stepper motor is fixed, as n Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)oted in the foregoing discussion. Microstepping provides much smaller step angles. This is achieved by changing the phase currents by small incrementsClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
(rather than on, off, and reversal) so that the detent (equilibrium) position of the rotor shifts in correspondingly small angular increments.7.2.1 SActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)gnetic character of the rotor. Specifically, a variablereluctance (VR) stepper motor has a soft-iron rotor while a permanent-magnet (PM) stepper motor has a magnetized rotor. The two types of motors operate in a somewhat similarActuators467manner. Specifically, the stator magnetic field (polarity) i Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)s stepped so as to change the minimum reluctance (or detent) position of the rotor in increments. Hence, both types of motors undergo similar changesClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
in reluctance (magnetic resistance) during operation. A disadvantage of VR stepper motors is that since the rotor is not magnetized, the holding torquActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2) conditions unless mechanical brakes are employed. A hybrid stepper motor possesses characteristics of both VR Steppers and I’M steppers. I he rotor of a hybrid stepper motor consists of two rotor segments connected by a shaft. Each rotor segment is a toothed wheel and is called a slack. The two rot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)or stacks form the two poles of a permanent magnet located along the rotor ax is. I lence, an entire slack of rotor teeth is magnetized to be a singleClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
pole (which is different from the case of a I’M stepper where the rotor has multiple poles). The rotor polarity of a hybrid Stepper can be provided eActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)ic-field along the rotor axis.Another practical classification that is used in this btxik is based on the number of "stacks" of teeth (or rotor segments) present on the rotor shaft. In particular, a hybrid stepper motor has two stacks of teeth. Further sub-classifications are possible, depending on Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)the texith pitch (angle between adjacent teeth) of the stator and texith pitch of the rotor. In a single-stack stepper motor, the rotor tooth pitch anClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
d the stator tooth pitch generally have to be unequal so that not all teeth in the stator are ever aligned with the rotor teeth at any instant. It is ActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)(stable equilibrium) position corresponding to that particular polarity distribution of the stator. In multiple-stack stepper motors, operation is possible even when the rotor tooth pitch is equal to the stator tooth pitch, provided that at least one stack of rotor teeth is rotationally shifted (mis Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)aligned) from the other stacks by a fraction of the rotor tooth pitch. In this design, it is this inter-stack misalignment that generates the drive toClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
rque for each motion step. It should be obvious that unequal-pitch multiple stack steppers are also a practical possibility. In this design, each rotoActuatorsStudy Objectives•The purpose of actuators in a mechatronic system•Types of actuators•Stepper motors and de motors (including brushless de mot Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2).7.2.2Hybrid Stepper MotorI lybrid steppers are arguably the most common variety of stepping motors in engineering applications. A hybrid stepper motor has two slacks of rotor teeth on its shaft. The two rotor stacks are magnetized to have opposite polarities, as shown in Figure 7.2. There are two s Clarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)tator segments surrounding the two rotor stacks. Both rotor a nd stator have teeth and their pilch angles arc equal. Each stator segment is wound to aClarence-W-de-Silva-Mechatronics-A-Foundation-Course-CRC-Press-2010-(F 2)
single phase, and accordingly, the number of phases is two. It follows that a hybrid stepper is similar in mechanical design and stator winding to aGọi ngay
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