Introduction: An Expensive “Ornament”

 

In the automation industry, robotic polishing workstations are a field that elicits both love and hate.

“Love” lies in its direct address of manufacturing’s biggest pain points: the “three high” positions—high intensity, high dust levels, and high hazards—where manual grinding makes it difficult to recruit workers, retain them, and maintain consistent product quality.

The “hatred” stems from its extremely high failure rate. We’ve seen too many project sites where million-dollar investments—expensive six-axis robots (even those from the “Big Four” brands)—were given high expectations, only to end up as costly “ornaments” sitting idly beside the production line, having produced defective parts riddled with issues such as “overcutting,” “incomplete grinding,” and “uneven surfaces.”

 

Where's the problem?

When engineers are frantically debugging robot paths and troubleshooting the logic in control cabinets, they often overlook... The real game-changer that determines success or failure. —The “final 10 centimeters” connected to the robot’s flange— End-of-Arm Tooling (EOAT).

If the robot’s body is its strong “arm,” then the end effector is its delicate “hand.” You can’t expect to use a hammer to perform intricate carving.

 

Today, we’re going to thoroughly explain the “hand” of robotic polishing. This selection guide could very well be the first cornerstone for your project’s success.

Key highlights of this article:

Why is the “hand” more important than the “arm”? Deconstruct the essence of the polishing process.

A Comprehensive Overview of the Mainstream “Hand”-Shaped Large-Scale Platforms: From “passive fluctuation” to “active constant force”—understand all five sects at a glance.

Selection Decision Model: Four dimensions to help you pinpoint your “perfect hand.”

Three “Avoid Pitfalls” Guides: 90% of project failures stem from these three traps.

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I. Redefinition: The essence of polishing is “force control,” not “position control.”

 

We're going to overturn a common belief: Robotic polishing is, in essence, not a “position-control” task but rather a “force-control” task.

Position Control: A robot cares about only one thing—“Has my end-effector TCP reached the programmed (X, Y, Z, A, B, C) coordinates?” This is the robot’s instinct, and it applies to tasks such as material handling and welding.

Force Control: The robot needs to check—“Is the force (in newtons, N) exerted by my tool on the workpiece surface constant?”

 

Why must polishing be done with controlled force?

Because the real world is “inconsistent.”

Inconsistent incoming materials: Especially with castings and forgings, the size and location of burrs, flash, and weld seams vary dramatically from one piece to another.

Inconsistent clamping: The positioning of a workpiece in a fixture will always have errors ranging from micrometers to millimeters.

Inconsistent abrasive wear: During the grinding process, sanding belts and sandpaper continuously wear down, and their “height” changes in real time.

 

If you use a rigid robot controlled purely by position to forcefully “bump” into an inconsistent workpiece, the result will be catastrophic:

The error is small (the workpiece deviates by 0.5 mm). With rigid contact, the force can instantly surge to several hundred kilograms, causing the workpiece to be “overcut” (a chunk of material being bitten off) or the tool to shatter.

The error is large (the workpiece deviates by 0.5mm). The tool and the workpiece “missed each other,” resulting in “undergrinding.”

Therefore, a qualified grinding EOAT must have... Primary task It’s about resolving this “inconsistency” and providing “flexibility.”

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II. The Five Major Schools: A Deep Dive into the Mainstream Polishing of EOAT

EOATs on the market come in a wide variety, yet no matter how much they differ, they all share a common foundation. Based on their underlying “flexibility” principles, we classify them into the following five major schools.

 

1. Passive Flexible Style: Pneumatic/Electric Floating Grinding Head

This is currently the most widely used and “down-to-earth” solution.

Core principle: The tool itself (such as an electric spindle) is mounted on a “floating mechanism.” This mechanism—typically a cylinder or spring—allows the tool to “extend and retract” in a certain direction (usually the Z-direction, i.e., perpendicular to the workpiece surface).

Work mode: You set a “pre-tightening force” by adjusting the air pressure (e.g., 0.4 MPa). The robot simply follows a rough path; when it encounters the workpiece, the grinding head automatically “retracts,” using the air pressure as a “buffer” to conform closely to the surface.

Advantages:

Low cost: Relatively simple structure and affordable price.

Durable and tough: Good tolerance to dusty environments.

Simple programming: The robot programming requirements aren't high— even a somewhat “rough” path will do.

Disadvantages:

“Fake” Hengli: It is “passively controlled.” Its pressure is strongly correlated with the compression stroke (the more the cylinder/spring is compressed, the greater the force), making it impossible to achieve true constant-force output on complex curved surfaces.

Precision limited: The hysteresis of pneumatic components results in a slow force response.

Applicable scenarios:

Large-area, relatively flat surface treatment.

Heavy-duty grinding and weld removal (does not require high consistency in force, but focuses on “removing” the material).

Projects with limited budgets.

 

2. Active Constant Force Faction: Constant Force Grinding Kit (Active Spindle)

These are players in the “high-end arena”—truly “intelligent” tools in the real sense.

Core principle: The tool itself is integrated. High-precision force sensor and Servo closed-loop system It’s no longer a “foolproof” cylinder—it’s a miniature robot.

Work mode: You directly set a force in the program—for example, “I need a constant 5 newtons.” No matter how much the robot’s path deviates or how uneven the workpiece surface may be, this grinding tool will, thanks to its built-in servo motor, Proactive 、 Real-time (On a millisecond scale) adjust its extension length to... Maintain That 5N force.

Advantages:

True Hengli: Extremely high force control accuracy and consistency—this is the guarantee for achieving high surface finish (Ra value).

Simple programming: Greatly reduces the requirements for robotic path accuracy.

Disadvantages:

Expensive: The price could be several times, or even dozens of times, that of a passive floating head.

Relatively delicate: Particular attention must be paid to tolerance of environmental factors such as dust and impact.

Applicable scenarios:

Fine polishing of 3C electronics (phone frames, tablet casings).

Precision polishing of aerospace (blade) components.

Mirror polishing of complex curved surfaces, such as bathroom hardware (faucets).

 

3. Leveraging Force-Generating Martial Arts Style: Robot Force/Torque Sensor (F/T Sensor) + Rigid Tool

The idea behind this approach is: The tool itself can be “dumb” (such as a simple angle grinder), but I make the robot’s “wrist” “smart.”

Core principle: Install a **six-axis force/torque sensor** (F/T Sensor) between the robot’s sixth-axis flange and the end effector.

Work mode: The sensor “perceives” in real time the forces acting on the tool in all directions (X, Y, Z translation and X, Y, Z rotation). This force signal is fed back to... Robot controller (Note: This is not a tool controller.) The robot controller enables advanced force control packages (such as ABB’s Force Control and KUKA’s .ForceControl) to make real-time adjustments. The pose of the robot's body Adapt to the workpiece to achieve constant-force contact.

Advantages:

Extremely flexible: Its 6-axis “haptic” capability enables it to handle even the most complex tasks, such as “edge-following deburring” (autonomously locating and following the edges of burrs).

General-purpose tool: In theory, any rigid tool can be used (for grinding, assembly, and inspection).

Disadvantages:

Programming Hell: The programming skills required of integrators are extremely high; they need to be proficient in the robot’s advanced force control package, and the debugging cycle is lengthy.

High cost: High-precision F/T sensors and advanced robotic software packages are both quite expensive.

Response speed: The entire robot starts moving, and its response speed is typically slower than that of an “active constant-force polishing kit” (where the tool itself moves).

Applicable scenarios:

R&D, small-batch production, and highly flexible production lines.

Complex deburring with completely random burr locations on workpieces.

 

4. Efficiency delivered to your doorstep: Dedicated belt grinder/angle grinder/planetary grinding head

This school does not adhere rigidly to force-control methods (which are often used in combination with the first three schools); instead, it focuses on the “tool form” itself to achieve specific manufacturing processes.

Belt Grinder:

Features: Grinding is performed using a high-speed rotating abrasive belt, with the contact surface being either a “line” or a “surface.”

Advantage: It boasts extremely high grinding efficiency and excellent heat dissipation, making it ideal for removing large material allowances and for grinding flat or regularly shaped external contours.

Angle Grinder:

Features: This is what we commonly refer to as an “angle grinder,” which uses disc-shaped grinding wheels.

Advantage: High power and high rigidity, ideal for heavy-duty grinding applications such as weld seams and sprues.

Planetary Grinder:

Features: Multiple small grinding heads (such as scouring pads) perform a “revolutionary + rotational” motion on a large baseplate.

Advantage: Evenly coated surface with no directional grain, specifically designed for wire drawing and surface finishing (sanding).

 

5. Exquisite and Agile School: Compliance Deburring Tools

This is the lightest and most underrated faction.

Core principle: Typically, these are non-powered. The cutting head (blade or rotary file) is mounted on a “flexible” handle that is spring- or pneumatically loaded, allowing the cutting head to float in multiple directions—X, Y, and Z.

Work mode: The robot only needs to follow an “approximate” path along the edge of the part; the flexible tool holder will automatically “grip” the edge and “scrape” away the burrs.

Advantages:

Extremely low cost: Simple structure.

Specifically treats small splinters: It works exceptionally well for removing fine, uniform burrs generated after machining operations such as drilling and milling.

Disadvantages:

Limited ability: It can only “deburr,” but cannot “grind” or “surface-treat.” It’s powerless when it comes to dealing with large flash from casting.

Applicable scenarios:

Deburring the holes and edges of machined parts (such as engine cylinder blocks and valve bodies).

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III. The Wisdom of “Choosing” Hands: A Four-Dimensional Decision-Making Model

Now that you’ve learned about the “Five Major Sects,” how should you choose the “right one” for your own application? Please use this four-dimensional decision-making model.

 

Dimension 1: Process Goal — What exactly is the effect you’re aiming for?

This is the primary issue.

Heavy Grinding/Deburring: The goal is to quickly remove large amounts of metal.

Preferred: School 4 (High-Power Angle Grinder/Belt Sander) + School 1 (Passive Floating, Ensuring the Tool Doesn't Stick).

Deburring:

Small burrs from machining: School of Thought 5 (Flexible Deburring Blade) is the king of cost-effectiveness.

Casting large flash: School 1 (passive float) + School 4 (small angle grinder).

Surface Finishing/Brushing: The goal is to achieve a uniform surface texture with a specific Ra value.

Preferred: Faction 2 (Active Constant-Force Polishing Kit) or Faction 1 (High-Precision Passive Floating Head).

Mirror polishing: The goal is extremely high gloss.

Required: School of Martial Arts 2 (Active Constant-Force Polishing Kit)—there’s no other way.

 

Dimension 2: Workpiece Characteristics—Who is your “opponent”?

Material: Soft metals such as aluminum and magnesium (prone to adhesion, requiring explosion-proof measures) vs. stainless steel and cast iron (hard, with rapid abrasive wear) vs. composite materials (easily delaminated)—this determines the EOAT's... Rotational speed and Power 。

Geometric shapes:

Flat/Simple shape: School of Thought 1 (passive floating) is sufficient.

Complex Surfaces/Inner Holes: Only Sect 2 (Active Constant Force) or Sect 3 (Force-Control Flange) can handle it.

Incoming material consistency (the key to the key):

High consistency (e.g., machined parts): The EOAT has low flexibility requirements.

Poor consistency (e.g., castings): Must Choose a highly flexible, large-stroke floating mechanism (Martial Art Style 1 or 2); otherwise, it’ll be a disaster.

 

Dimension Three: Core Demand — Efficiency, Cost, or Precision?

You can’t have it all—“both this and that and the other thing.”

Pursuing ultimate precision/consistency: Select Sect 2 (Active Constant Force), at the cost of sacrifice.

Pursuing ultimate efficiency: Select faction 4 (high-power belt grinder)—this may come at the cost of some flexibility.

Pursuing cost-effectiveness/quick payback: Choose Sect 1 (passive floating) or Sect 5 (flexible blade), and under the premise of meeting the technical requirements, use the most mature solution.

 

Dimension Four: The Integrated “Ecosystem”—Have you considered “changing hands”?

Polishing is not a single action—it’s an “ecosystem.”

Automatic Tool Changer: Does your workpiece require “rough grinding” (using a belt sander) → “fine finishing” (using a scouring pad) → “deburring” (using a small milling cutter)?

If so, you’ll need to consider an “automatic tool changer.” All the EOATs you select must be compatible with the quick-change system’s “air, electrical, and signal” interfaces.

Abrasive Changer: Sandbelt/sandpaper is a consumable.

When selecting an EOAT, ask yourself: Does it support automatic belt replacement, or does it require manual machine shutdown for belt changes? This directly determines your... OEE (Overall Equipment Effectiveness) 。

Dust Collection:

A good EOAT must come with an integrated dust-shielding cover design that can capture the vast majority of dust at its source. This is not only crucial for environmental and safety considerations—especially in preventing aluminum powder explosions—but also vital for product quality, as dust contamination can affect the surface of workpieces.

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IV. The Three “Selection Traps”: Don’t Let Your “Hands” Shackle the Robot

Finally, we’ve summarized three of the most common lessons from failures to help you “avoid pitfalls.”

 

Trap 1: Rigid robot + Rigid tool = 100% failure

This is the most common mistake made by “beginners.” They think that all they need to do is buy a high-precision robot and a high-precision spindle, then use a “taught” path to simply “graze” the workpiece.

Let me reiterate: Without a flexible grinding system, you’re 100% guaranteed to fail. Any error of even 0.1 mm could cause the force control to collapse. You must ensure that, among the robot, the tool, and the fixture, At least let one of them “soften up.” And the EOAT—that’s precisely the area that should be the “softest.”

 

Trap 2: Using “passive floatation” to achieve the effect of “active constant force.”

This is a classic case of “budget mismatch.” The customer brought in an iPhone middle frame and requested a mirror-polished finish—but only allocated a budget for the integrator to purchase a “passive air-bearing grinding head.”

It must be clarified: The “floating” of a cylinder and the “constant-force” of a servo are two entirely different concepts. The former relies on “cushioning,” while the latter depends on “closed-loop control.” Attempting to force the effect of one onto the other is like trying to catch fish by climbing a tree.

 

Trap 3: Focusing only on polishing while forgetting to “change the blade” and “remove dust.”

This is a failure of “systems thinking.” In the early stages of the project, engineers focused solely on the polishing head itself, forgetting that it’s part of an “ecosystem.”

Only after the project went live did we discover that every 5 minutes of robot grinding would dull the abrasive belt, requiring manual intervention to replace it—resulting in a dismal OEE. Or else, dust would fly everywhere, sensors would malfunction, guide rails would jam, and safety personnel would order an immediate shutdown.

Remember: An EOAT that cannot automatically change tools or efficiently remove dust—no matter how excellent its intrinsic performance—is still a “semi-finished product” in an industrial setting.

 

Conclusion

Robotic polishing is a field that “runs as deep as the ocean.”

The robot’s body (arm) determines your “workspace” and “inherent rigidity,” but... The end effector (hand) is what truly determines “what you can do” and “how well you can do it.” 。

This “hand” is not merely a “tool”—it embodies your entire understanding of craftsmanship. An understanding of flexibility, an understanding of force, an understanding of efficiency, and an understanding of systems and ecology.

Choose it wisely, and your million-dollar investment will truly be “intelligent manufacturing”; choose it wrong, and it’ll just end up being an “expensive ornament.”