Robotic Grinding: Contact Force and Wear Control
Direct answer: With the abrasive fixed and the robot carrying the part, there is no contact force setting. Contact comes from where the robot places the part and at what wrist angle. The part rides on the tangent of the wheel rather than being pushed into it, so paths run in short segments with a stable approach angle. As the abrasive wears the tangent moves, handled by a change interval, a compensating mechanism or a programmed offset.
Who this is for: Written for engineers and buyers planning a robotic grinding, deburring or polishing cell for small and medium metal parts.
Scope: This EVST guide covers how contact is produced and controlled in a grinding cell where the robot carries the part and the abrasive is fixed: which side moves, how posture sets contact, why paths are segmented, and how consumable wear is compensated. It does not quote contact forces, removal rates, surface finish results or cycle times; those depend on your part, your abrasive and your qualified process.
Two arrangements, and they are not interchangeable
A robotic grinding cell is built one of two ways. Either the abrasive is carried by the robot and taken to the part, or the part is carried by the robot and taken to a fixed abrasive. Almost every practical question downstream depends on which of the two you are looking at.
In the reference footage the second arrangement is used: the arm holds a cast steel handle type part and presents it to a fixed belt contact wheel, and later to a buffing wheel on the same station.
Carrying the part lets the abrasive be large, rigid and driven at a stable speed. The price is that part weight, gripping force and robot posture all enter the same accuracy chain, and the gripper has to hold the part against grinding reaction for the whole pass.
What robotic grinding contact force control actually is
There is no dial for contact force in this arrangement. Contact is the result of where the robot puts the part and at what angle it presents it, so a small position error changes both the pressure and the size of the contact patch at the same time.
That makes the object of commissioning a combination of position and posture rather than a force value. Turn the wrist a few degrees and a different area of the part meets the wheel, with a different local pressure.
Where the process genuinely needs a constant force, the cell adds compliance: an active or passive floating device at the end effector or on the abrasive side, which converts position error into a controlled force. Whether that is needed follows from how much your stock allowance varies, not from the robot.
This is also the reason a grinding cell cannot be specified from a robot datasheet alone. The same arm with a different gripper, a different part weight or a different wheel diameter produces a different contact condition.
Riding the tangent, and why paths are segmented
In the footage the part rides along the tangent of the wheel rather than being pushed into it. The contact point sits on the outer surface, the approach angle stays shallow, and the removal is spread along the pass instead of concentrated at one spot.
Holding that angle over a long sweep is difficult on a curved part, which is why these paths are broken into short segments. Each segment keeps its own approach angle inside a workable band, and the transitions between them are programmed deliberately.
Segmenting has a cost: the tie-in positions, the overlap between segments and the retract moves all have to be defined and then adjusted on real parts. That work is usually larger than a first estimate assumes and it is where most of the commissioning time goes.
The order EVST works in is the same each time: establish which side moves, then posture and contact, then segmentation, and only then the wear strategy.
| Part and process | Usual arrangement | What to verify first |
|---|---|---|
| Small or medium part, several faces, fixed abrasive available | Part on the robot, abrasive fixed | Gripping force against grinding reaction, and posture at each face |
| Large or heavy part that cannot be manipulated | Abrasive on the robot, part fixtured | Reach and stiffness at the far end of the part |
| Variable stock allowance or castings with flash | Either, plus active or passive compliance | How much the allowance varies and whether force has to stay constant |
| Several stages on one station | Part on the robot, multiple fixed abrasives | Wear rate of each stage and how offsets are maintained |
Consumables move the contact point
A belt dulls; a buffing or grinding wheel loses diameter. When the diameter changes, the tangent moves inward, and the taught point no longer produces the contact condition it was taught for.
There are three ways to handle it and they are not exclusive: change the consumable on a fixed interval, use a mechanism that advances the abrasive to compensate, or carry a wear offset in the program. Which is appropriate follows from consumption rate and how tightly the result has to be held.
A part that passes several stages needs a separate answer for each. Roughing removes stock, finishing corrects form, and the wheels differ in hardness and speed, so their wear rates and their compensation strategies differ too.
According to ISO 21920-1:2021, surface texture parameters are defined with the evaluation conditions stated, which is why a finish requirement has to name the parameter and the conditions rather than being quoted as a single number.
What belongs to the program and the process sheet
Contact force values, feed rates, stock removal per stage and wear compensation figures live in the program and the process documentation. None of them can be read from footage of a part being ground.
The same applies to results. Surface roughness and appearance grade are judged against a standard and a reference sample, not inferred from a video of the operation.
According to ISO 9283:1998, pose repeatability is measured under stated load and speed conditions, so any accuracy statement for a grinding cell has to name the tooling and the part weight it assumes.
In practice an EVST application review starts from the same inputs each time: part material, stock allowance and its variation, the abrasives already in use, and the finish requirement with its standard. The path strategy follows from that evidence.
Every application review opens from the same project inputs – drawing, standard and current method – so selection rests on evidence and acceptance is agreed against your own parts rather than a datasheet.
Safety around a grinding cell
Grinding cells add dust, sparks and rotating tooling to the usual robot hazards, and the part itself is being held by the gripper the whole time.
According to ISO 10218-2:2025, the safeguarded space of an integrated cell follows from the movement of the whole system, which here includes the part in the gripper and its swept volume, not the arm alone.
According to ISO 12100:2010, loss of grip, consumable failure and access for consumable changes belong to the same risk assessment as the robot motion rather than being handled afterwards.
Extraction and housekeeping usually decide how a grinding cell is laid out in practice, so they are worth settling with the layout rather than after it.
Frequently asked questions
Should the robot carry the part or the abrasive?
It follows from the part. Small and medium parts that a gripper can hold securely against grinding reaction are usually carried to a fixed abrasive, which allows a larger and more rigid tool. Large or heavy parts are fixtured and the abrasive is carried instead. Part weight, the number of faces and gripping security decide it.
Do we need force control, or is position enough?
It depends on how much your stock allowance varies. If the incoming condition is consistent, position and posture can hold the contact well enough. If allowance varies part to part, a floating or actively controlled device converts that variation into a controlled force instead of a variable one.
How is consumable wear usually handled?
By a change interval, by a mechanism that advances the abrasive, or by a wear offset in the program, and often a combination. A part passing several stages needs a separate answer per stage, because roughing and finishing wear at different rates.
What should we send to get a useful answer?
Part material and geometry, stock allowance and how much it varies, the abrasives and speeds in use today, and the finish requirement with the standard it is judged against.
Project inputs for an application review
To have this checked against your own part rather than a generic cell, send:
- part material, geometry and weight
- stock allowance and how much it varies between parts
- abrasives, wheel sizes and speeds currently used
- finish requirement and the standard it is judged against
Send the part material and stock allowance and the path strategy can be worked through against them. Related reading: robot welding workstation, automated factory integration.