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Exercise_7 - Exercise 7 A&EP 264 Spring,07 The Robot Arm...

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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 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
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: 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 We will use only one stop . bit and no parity bit The time interval for each bit is specified so that . a receiver may be synchronized with the transmitter In our case the / ( ); data transmission rate is 9600 bits second 9600 baud
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Exercise_7 - Exercise 7 A&EP 264 Spring,07 The Robot Arm...

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