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As the title indicates, this page covers both the Cliff-Sensor and the Wall-Sensor topics; and that is reasonable for several reasons. Perhaps foremost, is both devices employ the same operational tactic -- shoot an IR-beam away from the robot and look for a return -- in the form of scattered-radiance from a nearby object. Second, both types of device are mounted to Scooba's inner-bumper assembly. Third, Cliff-LEDs are wired in series with the Wall-LED; and finally, because they are both very much like their Roomba ancestors. The Cliff-Sensor will be discussed first.
A brief review of what a Cliff-Sensor Module contains, and how it works, might be appropriate here. The module contains an IR-LED (infrared light-emitting diode) which shines its tiny beam onto the floor, at an angle. In turn, the floor reflects, (more often 'scatters') that light upward, and fanned out over many three-dimensional angles, but with a high concentration of energy in the beam-angle that is equal in size, but opposite in sign, to the LED's pointing angle. A companion photo-transistor, PT, (oriented to view down onto the illuminated zone), then detects a portion of that scattered energy, and sends that information to Scooba's Controller (which becomes comforted by 'knowing' there is a floor beneath the robot!). If no IR-light is detected, the robot concludes 'there is no floor', then backs away from the threat of falling.
If these Scooba modules use the same pointing-angles as Roomba, the LED is beaming its output energy down onto the floor at a steep angle (roughly a 27° to 28° angle off vertical), and the PT views down at the illuminated spot at an equal, but opposite angle. Both angles being in a common plane, of course.
Unlike Cliff-Sensors on Roomba Floor Vacs, Scooba uses three sensor modules, instead of four. Figure 1 shows their positions along the arc of the inner-bumper's lower edge; one is front-center, and the others are at the trailing ends of the bumper, left and right. Note that the Bumper-Shell is not shown in this image, only the 'inner-bumper' portion is in place.
Figure 1. Three Cliff-Sensor Modules -- Center, Left, and Right, Inner-Bumper-Mounted
Based on the view of these modules from their underside, the Scooba-modules look identical to Roomba's. But, it would be hasty to claim that Scooba modules are the same as Roomba's. To illustrate that, let us look at the upper-edge of the inner-bumper, (the Bumper-Shell must be dismounted) so the tops of the modules can be seen. A major construction difference emerges. Scooba's Cliff-Sensor modules contain a small PWB ("Cliff-PWB", in this case) that is used to interface the harness connections to the two electro-optical components' connections; whereas Roomba's harness-wires solder directly to LED & PT pins!. Scooba's Cliff-PWB connections may be seen in an incidental, edge-on, capture of the RHS-module's PWB in Figure 3 (Bumper-Sensor page).
No Cliff-module has been removed from the inner-bumper to closely inspect it,
being inhibited from doing so partly due to the degree of sealant applied
along the upper edge of each module. We suspect that
LED-Pointing Reference: An out fall of the shift to the Cliff-PWB interface, is a difference in the directions that Scooba-LEDs' beams point (referring to the horizontal component of the beam vector) relative to the robot. Certainly, this is not critical information, but it could come in handy for troubleshooting at some future date. We notice that the right and left Cliff-LEDs are wired using RED & BLK insulation colors (however, there is a YEL jumper from the Wall-LED's cathode to the anode of the central Cliff-LED). That made it easy to see where those LEDs are placed and what their orientations are:
That says, if you (view down onto the bumper's top-edge) start at the LHS-module, call it the 9 o'clock station, then proceed clockwise to 12 o'clock (where the front module resides), then further clockwise to 3 o'clock, to the RHS module, you can see that all three LEDs point their beams clockwise, tangent to the arc just traveled. Of course, that makes the horizontal components of all three PT-views point anti-clockwise, so they can see their partner's signal. One thing this says is: All modules use a common PWB design! Another is: If an owner wishes to verify each LED is working, s/he now knows which way, and at what angle to aim a digital camera!
Troubleshooting: Scooba will tell you if the Cliff-Sensor's malfunction -- Error-Code "C" will be displayed. See page 19 of the Owner's- Manual for instructions. Should it become necessary to check each LED's output, with an IR-to-visual converter (such as a digital camera), they can be turned ON by pressing Scooba's Power button. No method is known for testing the PTs, other than the invasive process of elimination by shorting one PT, and doing a trial run, then repeating on the next PT until one is found that suppresses the error-code display while the PT is short-circuited.
Replacement Parts: If either device, LED or PT, should become inactive, we would not hesitate testing any of the following replacement possibilities (even in a Roomba):
The Wall Sensor operates in a manner similar to the Cliff-Sensor, so far as sending out an IR-beam, then acting on the back-scattered radiance, however it differs by not demanding the receipt of a return, yet when it does get that signal it helps the Controller navigate the robot along a nearby vertical surface.
Upon comparing the implementation of Scooba's wall-sensing hardware with a Discovery's similar hardware, two differences are obvious -- see Figure 2, where the Bumper-Shell has been dismounted to permit a view of Scooba's features.
Figure 2. Wall-Following Sensor's PWB Assembly
The shift to use of a printed wiring board was (likely) done to accommodate moisture protection, i.e., by application of a conformal, sealing coating over all exposed metal (soldered wire-ends, and the LED & PT lead-wires, between their bodies and their solder-pads.
To provide a little more information about the organization of parts locations on the Wall-PWB assembly shown in Figure 2, first recognize that Scooba's rear is to your left, and its front, mid-point is slightly off-frame to your RHS. Then, we may use the markings on the board to identify where the LED and PT are located.
At your left, you can see "A", and "K" lettered on the Wall-PWB. Those mark the solder-pads for the anode, "A", and cathode, "K" of the light-emitting diode. On the underside of the Wall-PWB, the LED is aimed to emit its radiance from the small, rectangular aperture seen under the Wall-PWB at that aft-end.
At the forward end of the Wall-PWB, letters "C" and "E" are visible. They denote collector, "C", and emitter, "E", connections to the photo-transistor. The PT is aligned to look out of the rectangular slot located just (to your) right of the attachment screw.
Regarding "troubleshooting" and/or "parts-replacement", Scooba seems to give no Error-Code for a malfunctioning Wall-Sensor. The LED's output could be checked in the manner described for the Cliff-Sensor, but the PT cannot. The T-1 body sized parts, listed in the Cliff-Sensor section should work in this assembly. It may be a moot cause, since failure of a Wall-Sensor is one of the rarest reported events in the plethora of Roomba faults.
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This page is currently maintained by G. Plews