Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Asphalt Paving Grade Sensor Placement

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Where should a Grade Sensor be placed on the screed? Topcon Grade Sensors: Sonic Tracker Contacting Sensor Smoothtrac SAS Laser Receiver mmGPS Receiver Fore and Aft Placement in reference to the tow arm Front, middle, or rear? End gate or Tow arm?

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Where should a Grade Sensor be placed on the screed? Rear of screed is desired grade position, relative to the grade reference The grade sensor needs to measure and control the screed position Grade control is adjusted by the cylinder at the front of the screed tow arm The grade sensor needs to measure the changes that have been made Curb – Grade Reference Desired Grade Grade Adjustment

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Where should a Grade Sensor be placed on the screed? The tow cylinder moves immediately as grade adjustments are made The screed will change grade as the screed moves forward Curb – Grade Reference Desired Grade Grade Adjustment

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Curb – Grade Reference Desired Grade Where should a Grade Sensor be placed on the screed? The tow cylinder moves immediately as grade adjustments are made The screed will change grade as the screed moves forward Grade Adjustment

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Curb – Grade Reference Desired Grade ? Grade Adjustment Where should a Grade Sensor be placed on the screed? The grade sensor needs to measure and control the screed position The grade sensor needs to measure the changes that have been made

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Curb – Grade Reference Desired Grade Grade Adjustment Grade Sensor placed at the back of the screed The grade sensor needs to measure and control the screed position

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Grade sensor positioned at the back of the screed No feedback indicating the tow point position has changed Tracker continues to apply grade corrections Curb – Grade Reference Desired Grade ? Grade Adjustment

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Curb – Grade Reference Grade sensor at the back of screed Will produce long waves A grade sensor can not be placed at the back of the screed X

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Curb – Grade Reference Grade Sensor placed at the tow cylinder The grade sensor needs to have position feedback from the cylinder it is controlling The grade sensor can keep the tow point exactly at the desired grade Grade Adjustment

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Curb – Grade Reference Grade Sensor placed at the tow cylinder Changes in the forces acting on the screed still exist! Manually adjusting the thickness adjustment screws changes screed height Grade sensor continues to control tow cylinder keeping it on desired path The grade sensor does not see changes in screed position Increase in material height Screed rises Pivot point

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Grade sensor at tow cylinder No correction for changes in screed height A grade sensor can not be placed at the tow cylinder X Curb – Grade Reference

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Where should a Grade Sensor be placed on the screed? The grade sensor needs to measure and control the screed position The grade sensor needs to measure the changes that have been made Curb – Grade Reference Screed position Grade Adjustment

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Rule of Thumb = Middle 1/3 of the tow arm Sensor has feedback of screed height Sensor has feedback of grade control changes 1/3

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Sensor placement affects screed reaction Grade sensor maintains distance to the grade reference Sensor position becomes control pivot point = effective tow arm length 3’ 9’ effective tow arm length d Grade Reference

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Grade sensor at rear 1/3 of screed - Step disturbance change in grade Sensor sees step disturbance, unit of 1 Sensor drives the tow cylinder until the sensor raises 1 unit Tow cylinder raises 3 units = large change in screed angle of attack 3’ effective tow arm length d

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Step disturbance change in grade – Sensor raises unit of 1 With increased angle of attack, screed begins to raise Grade Sensor lowers cylinder to maintain desired distance from reference After 1 tow arm length (3’), screed has risen 63% of the grade change One tow arm length d

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Step disturbance change in grade – Sensor raises unit of 1 Grade Sensor continues to lower cylinder as the screed rises to maintain desired distance from reference After 2 tow arm lengths (6’), screed has risen 87% of the grade change One tow arm length d

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Step disturbance change in grade – Sensor raises unit of 1 Grade Sensor continues to lower cylinder as the screed rises to maintain desired distance from reference After 3 tow arm lengths, screed has risen 95% of the grade change d 9’

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Sensor placed farther back – Screed is more reactive Screed quickly and accurately follows grade reference Jobs with quick changes in grade; city streets, parking lots, etc. 3’ 9’ effective tow arm length

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Grade sensor forward, 2/3 of screed - Step disturbance change in grade Sensor sees step disturbance, unit of 1 Sensor drives the tow cylinder until the sensor raises 1 unit Tow cylinder raises 1.5 units = small change in screed angle of attack effective tow arm length d 6’

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Grade sensor forward, 2/3 of screed - Step disturbance change in grade After 3 tow arm lengths, screed has risen 95% of the grade change 6’ 18’

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement effective tow arm length 6’ Sensor placed farther forward – Screed is less reactive Screed is slower to respond to grade deviations Jobs where smoothness is primary concern Good job practice regarding Principles of Paving is more critical 9’

Grade Sensor Placement rev Aug 2009 What is the best place to mount a grade sensor – Tow arm or end gate? Two primary factors; Stability of sensor Grade reference location Grade Sensor Placement

Grade Sensor Placement rev Aug 2009 tow arm end gate tow arm end gate Tow arm or end gate? In theory, the tow arm and the screed extensions are one rigid unit As tow arm raises and lowers, extensions and end gate move together Grade Sensor Placement tow arm end gate

Grade Sensor Placement rev Aug 2009 tow arm end gate Flex between tow arm and end gate can occur Wear in crank and adjustment bushings As screed extension is extended out, physical structure is not as strong Grade Sensor Placement

Grade Sensor Placement rev Aug 2009 Tow Arm or End Gate? Two primary factors Stability of sensor – Tow arm is always best choice Grade reference location – When the grade reference changes position relative to the paver, such as curbs with lane changes, the end gate is a more practical solution

Grade Sensor Placement rev Aug 2009 mmGPS or Laser Sensor Mounting Tow arm is always best choice Laser receiver or mmGPS – Grade reference location is not a problem Stability of the sensor is primary concern

Grade Sensor Placement rev Aug 2009 Grade Sensor Placement Asphalt Paving Grade Sensor Placement