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英文资料圆钢送料机械手-上下料机械手大学设计.doc
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1、英文资料The contral techniques drives and contrals handbookChapter A4Torque, speed and position controlA4.1 General principlesA4.1.1The ideal control systemMany applications exist where something has to be controlled to follow a reference quantity. For example, the speed of a large motor may be set from
2、 a low-power control signal. This can be achieved using a variable-speed drive as described in the following.矚慫润厲钐瘗睞枥庑赖。Ideally, the relationship between the reference and the motor speed should be linear, and the speed should change instantly with changes in the reference. Any control system can be
3、 represented as in Figure A4.1b, with an input reference signal, a transfer function F and an output. For the system to be ideal, the transfer function F would be a simple constant, so that the output would be proportional to the reference with no delay.聞創沟燴鐺險爱氇谴净。Figure A4.1 Variable-speed drive an
4、d motorA4.1.2Open-loop control Unfortunately, the transfer function of many practical systems is not a constant, and so without any form of feedback from the output to correct for the non-ideal nature of the transfer function, the output does not follow the demand as required. Using an induction mot
5、or supplied bya simple open-loop variable-speed drive as an example, the following illustrates some unwanted effects that can occur in practical systems:残骛楼諍锩瀨濟溆塹籟。Speed regulation. The output of a simple open-loop drive is a fixed frequency that is proportional to the speed reference, and so the fr
6、equency applied to the motor remains constant for a constant speed reference. The speed of the motor drops as load is applied because of the slip characteristic of the motor, and so the speed does not remain at the required level. 酽锕极額閉镇桧猪訣锥。Instability. It is possible under certain load conditions
7、and at certain frequencies for the motor speed to oscillate around the required speed, even though the applied frequency is constant. Another major source of instability in rotating mechanical systems is low-loss elastic couplings and shafts. 彈贸摄尔霁毙攬砖卤庑。Non-linearity. There are many possible sources
8、 of non-linearity. If, for example, the motor is connected to a gearbox, the speed at the output of the gearbox could be affected by backlash between the gears. 謀荞抟箧飆鐸怼类蒋薔。Variations with temperature. Some aspects of the system transfer function may vary with temperature. For example, the slip of an
9、 induction motor increases as the motor heats up, and so for a given load the motor speed may reduce from the starting speed when the motor was cold. 厦礴恳蹒骈時盡继價骚。Delay. With a simple open-loop inverter and induction motor there can be a delay before the motor speed reaches the demanded level after a
10、change in the speed reference. In very simple applications such as controlling the speed of a conveyor belt, this type of delay may not be a problem. In more complex systems, such as on a machine tool axis, delays have a significant effect on the quality of the system. 茕桢广鳓鯡选块网羈泪。These are just some
11、 of the unwanted effects that can be produced if an open-loop control system is used. One method that improves the quality of the controller is to use a measure of the output quantity to apply some feedback to give closed-loop control.鹅娅尽損鹌惨歷茏鴛賴。A4.1.3Closed-loop control The simple open-loop drive o
12、f Section A4.1.2 can be replaced with a control system as in Figure A4.2. This control system not only provides a means to correct for any error in the output variable, but also enable a stable response characteristic 籟丛妈羥为贍偾蛏练淨。A4.2 Controllers in a driveA4.2.1GeneralAlthough a modern variable-spee
13、d drive includes many features, the basic function of the drive is to control torque (or force), speed or position. Before proceeding to the specific details of how different types of variable-speed drive function, the theory of control for each of these quantities is discussed. A position control s
14、ystem is shown in Figure A4.5. This includes an inner speed controller, and within the speed controller there is an inner torque controller. It is possible to create a system where the position controller determines the mechanical torque that is applied to the load directly without the inner speed a
15、nd torque loops. However, the position controller would need to be able to control the complex combined transfer function of the motor windings, the mechanical load and the conversion from speed to position.預頌圣鉉儐歲龈讶骅籴。Therefore it is more usual to use the format shown in Figure A4.5. The other advan
16、tage of this approach is that limits can be applied to the range or rate of change of speed and torque between each of the controllers. When a system is required to control speed only, the position controller is omitted, and when a system is required to control torque only, the position and speed co
17、ntrollers are omitted.渗釤呛俨匀谔鱉调硯錦。A position sensor is shown providing feedback for the system, but this may be replaced by a speed sensor or it may be omitted altogether as follows.铙誅卧泻噦圣骋贶頂廡。Position information is required by the torque controller to function in an a.c. motor drive (see the dotted
18、 line). If position feedback is provided the speed feed-back is derived as the change of speed over a fixed sample period. Sensorless schemes are possible for speed and torque control of a.c. motors, in which case the sensor is not required. 擁締凤袜备訊顎轮烂蔷。Position feedback is not necessary for the torq
19、ue controller in a d.c. motor drive, so a speed feedback device such as a tacho-generator can be used to provide the feed-back for the speed controller. Again, sensorless schemes are possible where a speed feedback device is not required. 贓熱俣阃歲匱阊邺镓騷。A4.2.2Torque controlA torque controller for a rota
20、ry motor, or a force controller for a linear motor, is the basic inner loop of most variable-speed drives. Only torque control is discussed here, but the principles also apply to force control for a linear application. In order to explain the principles of torque control, the simple d.c. motor syste
21、m in Figure A4.6 is used as an example. The analysis of torque control in an a.c. motor can be done in exactly the same way, provided suitable transformations are carried out in the drive. These transformations will be discussed later.坛摶乡囂忏蒌鍥铃氈淚。The torque demand or reference (Te*) is converted by t
22、he torque controller into a current in the motor armature, and the motor itself converts the current into torque蜡變黲癟報伥铉锚鈰赘。Figure A4.6 Torque and current controllers in a d.c. motor drive: (a) torque control;買鲷鴯譖昙膚遙闫撷凄。(b) current control to drive the mechanical load. Figure A4.6b shows the system r
23、equired to convert the torque reference into motor current. The torque reference (Te*) is first transformed into a current reference (ia*) by including the scaling effect of the motor flux. The motor flux, controlled by the motor field current (if ), is normally reduced from its rated level at highe
24、r speeds when the terminal voltage would exceed the maximum possible output voltage of the power circuit without this adjustment. Current limits are then applied to the current reference so that the required current does not exceed the capa-bilities of the drive. The current reference (limited to a
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