Force sensor

Can anyone recommend a sensor for measuring the weight of an object being moved in a pick and place application?

The robot is a scara type (adept Cobra 800)

The object is a silicone wafer (approx 10 grams)

It is held by vacuum suction cups

There will be non moving times of approx. 0.5 sec when this could be done, otherwise acceleration or deceleration would need to be considered. I'm not sure if everything settles out in this time but maybe that could taken care of with software.

Oh yeah, the interesting part, accuracy +/- 0.50 grams

I've heard of load sensors with onboard accelerometers to cancel out the moving effects but haven't investigated them yet.

Anyone done anything like this? Any manufacturers to recommend?

TIA Farmer (remove obvious to reply)

Greetings all,

The url for the sensors lyndon mentioned is:

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-- warning, this is not (IMHO) a hobbiest-friendly site, at least not as of my last visit. (As I recall, one had to search pretty hard to find the order form. $60 minimum, last I looked.) Try searching for "FSR Design Kit" The sensors are, however, reasonably close to what you want. In particular, check out models 400 and 402 (402 is .5 inch dia., a bit over your 10 mm. spec.) These devices don't have great DC repeatability, but they may well suffice, *provided* you make the distribution of the force repeatable as possible. I've done this by sandwitching the sensor between a flat (stiff) plate, and a softer, rounded "foot" (interlink calls this an actuator.) I've used self-adhesive "feet" for electronic boxes for this. Doing this means that the sensor is not quite at the end of your assembly, so the outboard mass will change readings slightly during accelerations; however, that outboard mass can give both more repeatible readings, as well as shield the sensor from wear &tear.

Note also that the op-amp-based linearizing circuit (see their "Integration Guide and Evaluation parts catalog" makes the output much nicer to work with, at a very modiest hardware cost.

Another company that makes similar sensors is tekscan; see

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-- look at their flexiforce product. Unsure whther they sell in small volumes.

HTH,

Larry