Door gap and flush
Closure fit across doors, hood, fenders and tailgate.
- Gap between panel edges
- Flush step between surfaces
- Taper and parallelism along the joint
- Minimum and maximum gap, edge radius
Gap and flush across doors, hood, fenders and tailgate — plus adhesive bead inspection and non-contact wheel geometry. Three applications, one sensing platform: a blue laser line, a robot to place it, and measurement tools that turn a profile into a decision the line can act on.
One laser line laid across the joint returns both values at once. The flat sections falling on each panel are the reference surfaces — no external datum is needed for the measurement itself.
All three share the same measurement physics. What changes is the feature being measured and the model that suits it.
Closure fit across doors, hood, fenders and tailgate.
Urethane bead applied to the glass or the pinchweld.
Non-contact toe and camber taken from the rim flange.
Gap and flushness are the most visible indicators of build quality on a finished vehicle. They are also functional — a joint out of tolerance drives wind noise, water ingress and seal wear long after the vehicle has left the plant.
The cost of correcting a closure fault rises sharply with how far down the line it is found. In framing, it is a shim and a few minutes. After paint, the panel cannot be adjusted without risking the finish. After trim, the door furniture comes off first. In the field, it is a warranty claim plus a customer who has already formed a view of the vehicle.
That curve is the argument for measuring at density and measuring early, rather than auditing a sample at the end. The value is not in catching the reject — it is in seeing a hinge or a fixture drift before it has produced a shift's worth of them.
Typical OEM practice around a single vehicle body.
Manual inspection at this density is not repeatable, and 2D vision cannot resolve a measurement that is fundamentally three-dimensional.
Two different geometric quantities, taken from one profile. Understanding why they behave differently is what governs sensor selection later.
Also derived from the same profile: gap taper along the joint, parallelism, minimum and maximum gap, edge radius and seal-line continuity.
Flush is a height difference between two surfaces, and each surface is fitted through thousands of points. Fitting averages noise away, so the practical flush figure is considerably better than any single-point height specification would suggest.
Gap is different. It is a lateral distance between two edges, and an edge is located from the data interval along the profile. There is no averaging to rescue it — the sampling across the line sets the finest resolvable edge position directly. This is why lateral resolution, not height repeatability, is usually the constraint that decides which sensor a given joint needs, and why sizing the field of view to the joint rather than to the panel matters so much.
Dark metallics absorb, clear coat reflects specularly, and the same joint may appear in a dozen different colours across a single shift.
The same panel, the same geometry. What changes is how far the light travels into the paint before it comes back, and therefore how precisely the edge can be located.
One robot-carried profiler covers every joint on the vehicle side. The measurement recipe for each pose is recalled by the sensor as the robot arrives.
A taught pose assumes the body arrives in the same place every time. It does not. Conveyor stop accuracy, carrier wear and body-in-white variation all move the joint relative to the robot, and because apparent gap widens as the sensor tilts away from normal, a pose error shows up directly as a measurement error.
The correction is a coarse six-degree-of-freedom scan as the vehicle arrives, establishing body pose before the sequence starts. That offset is passed to the robot controller, which corrects every taught approach in real time. Without it, you are measuring the conveyor's repeatability as much as the joint's fit — which is why sensor pose repeatability, not sensor specification, is usually the dominant error term in a station like this.
It comes down to two questions. How many joints must be covered inside the available takt, and how often does the joint layout change? A robot cell trades time for flexibility — every extra pose costs seconds, but a new model costs only re-teaching. A gantry trades flexibility for time — every joint is captured at once, but a new layout means new brackets and new sensors.
Where the model mix is wide or the programme is early, the robot cell almost always wins. Where takt is brutal and the layout is stable for years, the gantry does. The audit station is neither, and it is often the right first move regardless: it establishes correlation against your existing gauge at low cost, and that correlation is what the in-line business case is eventually argued on.
Sensor repeatability is not system accuracy. Station capability is built from several contributions, and each has to be controlled for the measurement to correlate with the gauge you already use.
Edge convention is the quiet cause of most correlation disputes. Your existing hand gauge or CMM defines the edge of a panel at some particular place — the tangent point, the end of the radius, a fixed offset from it. A profiler sees the whole radius and can define that edge anywhere on it.
Pick a different convention and every reading is offset by a consistent amount. The system is repeatable, the numbers are wrong against the existing gauge, and the disagreement surfaces during acceptance when it is expensive. Capturing the convention from your current method during the application study, and building it into the recipe, costs nothing at the start and settles the argument before it happens.
We state a capability figure only after a gauge R&R study on your own vehicles, correlated against your existing CMM or hand gauge. A number quoted before that study is a sales number, not an engineering one.
The same honesty applies to wheel geometry. Gap and flush and adhesive bead are established, published applications for this sensor family. Wheel geometry is an engineered application — we would rather say so now than discover it during acceptance, and we would propose an offline feasibility on your actual wheel set, correlated against your existing alignment machine, before any in-line commitment is discussed.
Urethane is dispensed as a continuous bead onto the glass or the pinchweld before the windshield is set. It is structural as well as sealing: it carries load in roof crush and gives the passenger airbag its reaction surface. A break, a necked section or a bead too close to the glass edge is a leak, a corrosion path, or a bond that does not meet its design case.
The bead path around a windshield aperture runs several metres. One break anywhere along it is a reject, which is why continuity is measured rather than sampled.
The dispense controller knows how much material it commanded. It cannot know how much arrived. A partially blocked nozzle, a temperature shift in the urethane, or a worn tip all produce a bead that looks present and is under-filled.
Cross-sectional area at each profile is the direct check on material actually deposited, which is precisely the measurement the dispense system cannot make about itself. Height alone is not enough: a bead that is tall and narrow can carry the same height reading as one that is correct and considerably less material.
Alignment is set and verified at end of line. Toe and camber outside specification produce tyre wear, steering pull and, increasingly, calibration errors in the driver assistance sensors that reference the vehicle's thrust line.
Each wheel plane is fitted locally; toe, thrust angle and track only exist once all four are expressed in one common frame.
Sensor height repeatability is not the limit here. Ten microns of noise across a rim chord of a few hundred millimetres works out to under two thousandths of a degree — far below anything the alignment specification cares about. Fitting a plane through thousands of flange points averages the noise away almost entirely.
What actually sets the accuracy is the extrinsic calibration between the four measuring stations, and the stability of the vehicle datum. Four locally perfect wheel planes are useless until they are expressed in one common frame, and that frame has to hold across shifts and temperature. Runout adds a second complication: rim eccentricity and mounting error appear directly as toe and camber error unless the wheel is rotated and the fit repeated at several angular positions.
This is also why we treat it as an engineered application rather than a catalogue one. Styled alloys and centre caps can obscure the flange, brake dust and road film degrade the return, and ride height settles after suspension load — so when you measure matters as much as how.
An application study on your joint list and tolerance table, with the edge convention captured from your existing gauge and a sample vehicle scanned. It answers the questions that decide whether a pilot is worth building — before anyone commits capital to a cell. Sensor selection, capability figures and programme detail are issued against your application, under a mutual confidentiality agreement.
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