Bannner IR sensor Measures Ball Exit Velocity
 

The banner IR sensor has a range ~1' using blue/green poof balls

(IR doesn't reflect from balls with a black half, Visible LED type may - TBD)

I conducted a test yesterday (prelim) using a 1+ meter AL pole over the ball exit path with 2 sensors attached directed downward,
1m apart
black output lead pull up = ~2.2mA, (produces neg. going ball pulse)
5.6k to 12v or 2.2k to 5v)

Oscilloscope used for time between their falling (leading) edges.
83.3ms = 12m/s (1/.0833)

NOTE: In lieu of Oscilloscope (or external electronic timer)
RC may be used with software to measure time:

between two sensors using 2 input ports (above)

or one port to measure pulsewidth for Simple method (below)

Example: measured 60ms on 12.5" skyway
direct driven by lg CIM at 12.6V (~2500 rpm)
so 1/.06 = 16.7m/s

The 2 sensor method eliminates
ball dia. and edge dropoff errors at cost of 2nd sensor
by measuring leading -edge start to leading -edge stop times

-----------------------

Simple 1 sensor method: (assumes sensor sees full 7" ball dia):
assumes 7" ball diameter =measured path leading to falling edge = pulsewidth

Also requires blue/green balls (IR reflection is not reliable with BLACK balls)

the Velocity in m/s is 1/(5.624*pulsewidth_sec)

1 / ( (39.37"/m /7"ball)*pulsewidth_sec)

Example: pulsewidth of 15 ms = 11.85m/s

12m/s = 83.3 ms/m /5.634 = 14.8ms for 7" ball path

realistically sensor likely senses a bit short of 7" due to the sphere edge slope. Measure the test ball(s) dia + Perform Edge detection test for an accurate dia. to use for better accuracy -- 6.9 or ?


note
select the white sensor output w/pullup R to +V for positive going pulses

Dale.Hall@earthlink.net
Team 294 Redondo Beach, CA

note:
m/s meters/sec
ms = millisec (1/1000 sec)

Re: Bannner IR sensor Measures Ball Exit Velocity
 

Do you think this would work using the banner retro reflector and sensing the ball as a blocker rather than a reflector? Then it wouldn't be sensitive to the black side of the ball.

Re: Bannner IR sensor Measures Ball Exit Velocity
 

Gary,
A separate emitter & detector would eliminate the black IR absorption problem
at the cost of a bit more complexity,

i.e. two wired & optically aligned devices per location
(+ may need to shield ambient w/ tube or use modulation)

(1 loc pulse width of 7" ball or
2 loc's for distance traveled reducing error from dia & beam pos on ball)

Some teams may only have balls that are half black.

then I suggest the simpler method, spray paint test ball (black half or all)

Verified - works/repeatable:
simpler: one device position per loc, self aligning / shielding (sensivity adj)
I set up this test in 15 min w/old real time scope (DSO or storage better)
I was impressed with the results of two sensor time repeatability and

promising 1 sensor approach using 7" ball width to measure exit velocity (pro: sensor close to exit, con: error if beam not centered on ball) looks very promising, i.e. "simple as possible but not simpler" A.E.

??? re: retro-refl
Our IR & Vis Banner Sensors contain emitter & detector & range adjustment in one compact package and rely on retro reflected beam.

Broken beam approach requires physically separate Emitter & Detector & likely a hood (or modulated?) and good stable optical alignment

Dale(294engr]

Re: Bannner IR sensor Measures Ball Exit Velocity
 

Thanks. We are playing around with this as well. The IR sensor is listed as "diffuse" and the visual red sensor is listed as "retro-reflective", but the wavelengths aren't much different between the 2 sensors while the range is significantly different, so I wasn't sure if there was some difference in design that would make them behave differently.
I wasn't sure if the detection spectrum was sufficiently different that it would react better to a specific retro-reflector target while ignoring a different diffuse target (the ball) by tuning the sensitivity.

Re: Bannner IR sensor Measures Ball Exit Velocity
 

I omitted this Banner IR sensor option:
Either sensor may be used with a reflector, i.e blocking mode. IR sensor is effective > 1' effective to detect all the ball colors, without separate Emiter / Detector (re: my earlier reply - just need to position reflector and look for loss of signal in code.)