{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture3 - Position and Velocity Measurements • Important...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Position and Velocity Measurements • Important in many embedded applications, especially those in which the microprocessor must interface to mechanical hardware. • Question: How many examples can you name?--- • Many microcontrollers have special features that expedite such measurements. • The MPC5553 has an enhanced Time Processing Unit (eTPU) that is essentially a special purpose microcomputer that operates simultaneously with the CPU. The eTPU performs special functions that otherwise would require CPU interrupt service.- Quadrature Decoding- many others... • Analog vs. Digital Measurement Technology- Signal/Noise ratio (S/N)- Dynamic Range (largest vs. smallest measurements) • Information about technology for position and velocity measurements can be found in many textbooks, including [1], [2], and [4]. Reference [1] was used primarily in developing this set of notes. EECS461, Lecture 3, updated September 12, 2007 1 Analog Velocity Measurement • Tachometer: produces a voltage proportional to velocity (usually rotational velocity) • same operating principle as DC motor; in fact, it is possible to use a DC motor as a tachometer. (will describe when we discuss DC motors) • tachometer performance is often limited by noise (e.g., brush noise) • at low velocities S/N ratio is poor, and it is difficult to determine when velocity is zero (i.e., when the mechanical system is stopped) EECS461, Lecture 3, updated September 12, 2007 2 Analog Position Measurement • Potentiometer: produces a voltage proportional to distance from a reference point • Example: Measure distance of a cart from one end of a track • Since there is a sliding mechanical contact, noise, dirt, humidity, and mechanical wear limit precision. • The maximum range is also limited! EECS461, Lecture 3, updated September 12, 2007 3 Optical Encoder • Often used for digital position and velocity measurement • Two types- absolute encoders: gives actual position- incremental encoders: gives change in position • Usually encoders measure angular displacement- can be used to measure rectilinear position- computer mouse (2-dimensional position!) • Will first discuss incremental encoder, because we will use in lab. EECS461, Lecture 3, updated September 12, 2007 4 Incremental Encoder • a wheel with little windows (front and side views): . LED light sensor • As wheel rotates, the photocell generates a digital signal: 1 • If windows and dividers are of equal width, then the “on” and “off” times are of equal duration for constant rotation rate....
View Full Document

{[ snackBarMessage ]}

Page1 / 21

Lecture3 - Position and Velocity Measurements • Important...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon bookmark
Ask a homework question - tutors are online