Exercise 7 - 8 - Exercise 7: Introduction to LabVIEW...

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: Exercise 7 Introduction to LabVIEW Chapters four through eight of LabVIEW for Everyone describe the techniques needed for construction of virtual instruments. Work through Activities 4-2, 5- 2, 6-2, 7-1, 8-2, and 8-4 to get a feel for the mechanics of the use and construction of LabVIEW VIs. : Exercise 8 The Robot Arm The virtual instrument system of LabVIEW lends itself . readily to the real time interactive control of a robot arm Our robot arm has five servo motors that control the ”, “ ”, “ ”, “ positions of the waist shoulder elbow wrist and ”. gripper This experiment illustrates the use of serial port communications for remote computer control of an external . device : The tasks to be mastered in this exercise are Learn how a character string may be used to generate -- - a bit sequence at a serial port an example of RS 232 . serial communications Use a series of bytes at the serial port output to separately control the positions of each of the five . servo motors Develop a virtual instrument that enables the user to generate a desired sequence of motions for the robot - . arm in real time Use a refined virtual instrument to generate a , smoothly controlled trajectory of motion which may be . recorded for automatic playback Use the robot arm to automatically move a selected - ( object between two user selected locations similar to - the wafer handling operation used in the semiconductor ). industry Principles of operation of the servo motors There are two common types of servo motors used for . various applications A stepper motor moves in discrete steps
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. in response to a series of voltage pulses Each voltage pulse . causes the rotor to rotate by a small fixed angular increment Your electric clock contains a stepper motor driven by voltage pulses . synchronized at the 60 Hz power line frequency The robot arm requires a second type of servo that may be rotated through a small fixed angular range in precise increments . in response to commands issued by the user The servo s position + is controlled by transmitting to it a 60 Hz train of 5 volt pulses of ; variable pulse duration a change in servo position requires a . change in the pulse width The pulse width may be varied between 1 and 2 milliseconds to operate the servo over its full . range of angular motion as illustrated in the Figure 1 This type of - . servo is referred to as a pulse proportional servo A controller , , card located on the robot arm assembly is used to generate the , desired pulse train in response to a pattern of serial data , transmitted one bit at a time from the serial output port of the . host computer : Figure1 Controller card output Serial data transmission - . We will use the RS 232C protocol A start bit indicates the ( ( )) beginning of a data word of 4 to 8 bits in our case 1 byte 8 bits . , that follows After the data word a parity bit used for error , . checking is sometimes inserted followed by one or two stop bits
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Exercise 7 - 8 - Exercise 7: Introduction to LabVIEW...

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