Use Separate FSR Zones When a Service Robot Must Locate Contact

Use separate FSR sensing zones when a service robot must identify where its bumper, contact bar or compliant pad is being loaded. A single continuous sensor area can answer “contact happened,” but it cannot show left, center or right contact unless the mechanical and electrical layout creates independent zones. Location data is useful only when each zone has a controlled actuator, a defined readout channel and a mounted threshold test.

The International Federation of Robotics World Robotics 2025 release reports that transportation and logistics was the largest professional service-robot application class in its 2024 supplier sample, while professional cleaning robot sales in that sample also increased. IFR states that the data came from 294 suppliers and should not be projected to the whole industry. For component buyers, the practical issue is not the market total. More mobile machines create more designs in which a thin contact-sensing layer must fit around limited housing space, cables and service panels.

A custom FSR pressure sensor can support relative contact detection in that mechanical stack. It is not automatically a calibrated force instrument or a safety-rated protective device. The buyer still needs to define what contact means, how the load reaches each sensing zone and what the equipment controller should do with the signal.

Start with the information the robot needs after contact

Do not divide a bumper into zones because the drawing has spare space. Divide it only when the controller or service team can use the location.

A single sensing area may be enough for a slow docking aid, an occupied-pad input or a non-safety contact indication. It uses fewer conductors and fewer readout channels. The limitation is that a signal from the left edge can look the same as a signal from the center once both loads reach the same sensing element.

Separate zones make sense when the machine needs to distinguish a corner touch from a centered touch, compare two sides of a compliant contact bar or identify which pad needs inspection. That added information costs connector pins, controller inputs, calibration records and production test time. If the software reacts identically to every zone, the extra segmentation may add complexity without adding a useful decision.

Write the required output first: one contact bit, a relative load trend, or a zone map. That choice controls the film layout and the electrical interface.

Give every sensing zone its own mechanical load path

An FSR responds to the pressure applied through the actuator above it. The printed sensor geometry alone does not decide how much of a bumper load reaches the active area. A soft skin, foam pad, molded rib, hard button or broad plate can produce different resistance changes under the same external contact.

For a multi-zone bumper or contact pad, show these parts in one section view:

• the outer bumper skin or touch surface;
• the actuator land above each sensing zone;
• the unloaded clearance or planned preload;
• the hard stop that limits excessive travel;
• the sensor support surface and adhesive area;
• the cable exit, strain relief and connector pocket.

The actuator should land inside its intended sensing zone without bridging the neighboring zone during normal travel. A wide soft pad spreads load and can smooth local peaks, but it may also make two zones respond together. A narrow hard rib separates locations more clearly, yet it can concentrate force and increase sensitivity to alignment. The sample must resolve that tradeoff in the real housing.

Keep preload and cable strain out of the zero signal

False contact often begins before the robot touches anything. A warped cover, compressed foam, tight mounting screw or adhesive stack can leave one FSR zone partly loaded at rest. The controller then treats housing stress as an obstacle or slowly loses threshold margin as the assembly settles.

Cable strain creates a different error path. Pulling a cable loop or forcing the connector into a shallow pocket can bend the film near the trace transition. Even when the active sensing pads remain untouched, the mechanical stack may change enough to shift the baseline or damage the connection. Route the cable so service access does not tug the sensor, and place strain relief outside the active zone and bend transition.

Record the unloaded reading after final assembly, not only on a bare bench sample. Repeat it after the bumper has been removed and installed again. If one zone returns to a different baseline, inspect preload, adhesive flatness, actuator alignment and cable routing before changing the software threshold.

Match separate zones to separate electrical evidence

Multiple visible pads do not guarantee multiple independent signals. The circuit may combine zones, share a return path or use a connector map that the buyer has not yet defined. A drawing should label each sensing area and show how it reaches the tail, cable and connector.

For location detection, the quotation package should state:

• zone names and center coordinates;
• whether each zone needs an independent output;
• the connector pin assignment and mating orientation;
• the controller excitation and readout method;
• the desired unloaded baseline review;
• the lightest contact that must be detected in the mounted assembly;
• any overload or hard-stop condition;
• the decision rule when two neighboring zones respond together.

FSR output is affected by actuator geometry, dwell, repeat loading, temperature and the readout circuit. Do not convert one bench resistance value into a universal force claim. If the project needs calibrated force measurement rather than relative threshold or trend detection, the sensor and full mechanical system need a separate calibration plan, and another sensing technology may be more suitable.

Test a contact map on the assembled bumper

A useful prototype test moves around the perimeter instead of pressing one convenient point. Mark the intended contact locations on the assembled bumper or pad, then apply the agreed test method at the left, center, right and between-zone boundaries. Log every channel, including channels that should remain quiet.

The boundary test matters because it exposes actuator overlap. If two zones respond at the midpoint, decide whether that is useful redundancy or an ambiguous location. Repeat the map with the robot panel fastened to production torque and with the cable secured in its intended route. A loose desktop setup does not reproduce housing preload.

Also test a no-contact service sequence. Open the service panel, unplug and reconnect the cable, refit the bumper and confirm that the unloaded baseline returns. For cleaning robots or warehouse equipment, include the permitted cleaning method and normal dust or moisture exposure in the mounted sample plan. The FSR layer does not replace enclosure sealing, a protective bumper, motion-control limits or any required safety function.

Send one zone-and-actuator package for review

Prepare one annotated drawing that links the visible contact surface to the electrical output. Include the robot or bumper outline, sensor perimeter, active-zone coordinates, actuator shape, section stack, hard stop, cable bend route, connector location and pin map. Add the operating voltage or readout circuit, target contact decision, expected quantity and the mounted acceptance test.

Attach a photo or CAD view showing where a hand, cart edge, docking fixture or obstacle can reach the contact surface. Identify the highest-risk location, such as the gap between two actuators or the corner nearest the cable exit. That tells the supplier which geometry must be protected during the first sample review.

Use the Request Quote page to send that zone-and-actuator package. Ask for the first sample to prove one decision: whether the selected zone layout can distinguish the required contact locations without preload or cable movement creating a false input. Only after that mounted map is stable should the team freeze the connector pins and controller thresholds.