What is a collaborative robot arm (cobot) and where does it sit in the market?
A collaborative robot arm—cobot for short—is an industrial robot designed to operate in close proximity to people without requiring full perimeter safety guarding in many applications. That is the defining commercial advantage over a traditional industrial robot: lower installation cost, faster deployment and the flexibility to reposition the arm as tasks change.
The trade-off is capacity. Cobots generally carry lower payloads and move at lower speeds than their fully-guarded counterparts. Their typical payload range suits a wide range of assembly, machine-tending, screwdriving and light palletising tasks, but rules them out for heavy handling that a traditional robot arm handles routinely.
Cobot does not mean safety-guarding waiver
A cobot's collaborative design reduces the need for fixed perimeter guarding in many configurations, but it does not automatically eliminate all guarding requirements. The specific application, tool, part geometry and operating speed all affect the risk assessment. Always direct buyers to conduct a formal risk assessment before deployment—that requirement sits with the end user, not the dealer.
What payload actually means—and why the headline number is only part of the answer
Payload is the total weight the arm can carry at its wrist flange while maintaining its rated speed and repeatability. The figure printed on the spec sheet represents the maximum under a specific set of conditions, typically with the load centred at the wrist and at a defined reach distance. It is not a flat ceiling that applies equally at every position in the arm's working envelope.
As the arm extends further from its base, the torque demand on each joint increases. Most manufacturers publish a payload-versus-reach curve, or at minimum a rated payload at maximum reach that is lower than the headline figure. A buyer who needs to carry a gripper-plus-part combination at near-maximum extension should not be sizing against the nominal payload rating without checking what that arm actually delivers at that distance.
There is a second weight that buyers frequently undercount: the end-of-arm tool, or tooling assembly. A gripper, camera, force-torque sensor or vacuum cup assembly all adds mass. That tool weight counts against the payload budget before a single part is picked up. Ask buyers to weigh their existing tooling, or estimate it from the tool manufacturer's data sheet, and subtract it from the cobot's usable payload at their required reach.
End-of-arm tooling weight is always part of the payload
A buyer who omits tooling weight from the payload calculation risks exceeding the cobot's rating in normal operation. Exceeding payload consistently causes premature joint wear and may trigger protective stops that interrupt production. Verify tooling weight before agreeing on a specification.
What reach means—and how to define the motion envelope your buyer actually needs
Reach is the maximum distance from the centre of the robot's base to the centre of its wrist flange at full arm extension. It defines the outermost boundary of the sphere within which the arm can move. A given reach figure describes a theoretical maximum—practical working range is smaller once you account for joint limits, mounting height and the geometry of the task.
To define the reach a buyer genuinely needs, they should map the full motion path of the task: the pick point, the place point and every intermediate position the arm must pass through. The required reach is the furthest distance between the robot's mounting point and any of those positions. Build in a margin rather than buying exactly to the edge of the envelope, because working at maximum extension reduces accuracy and payload capacity simultaneously.
Mounting position matters too. A cobot mounted on a riser, a ceiling bracket or a side-wall fixture shifts the effective working envelope relative to the floor and the task. A buyer who plans to ceiling-mount a cobot over a conveyor needs to confirm that the arm's reach and payload in inverted orientation match the manufacturer's specification for that mounting mode—not all models are rated identically in every orientation.
How payload and reach interact: the practical check a dealer should run
Before listing a used cobot or presenting it to a buyer, pull the manufacturer's published specification document—not a reseller's summary sheet. Locate the payload-at-reach table or curve. If the document only states maximum payload and maximum reach as two separate numbers without relating them, request the full data sheet from the manufacturer's technical library or a distributor; most publish them without charge.
- Identify the buyer's required reach distance: the furthest point in the task envelope from the robot's base mounting centre.
- Find the payload the arm delivers at that specific reach distance, using the manufacturer's payload-reach curve or table.
- Weigh the end-of-arm tooling assembly, or obtain its mass from the tool data sheet.
- Subtract the tooling mass from the usable payload at the required reach. The remainder is available for the part.
- Confirm the part mass (including any fixturing or packaging that travels with it) does not exceed that remainder.
- Check the manufacturer's specification for the intended mounting orientation if the buyer is not mounting the arm upright on a flat surface.
- If the application sits close to any limit—payload, reach or orientation—recommend a simulation or on-site trial before purchase.
How dealers should present cobot inventory by payload and reach
A listing that states only the headline payload draws the wrong enquiries. Buyers who need a specific load at a moderate reach distance will contact you about a machine rated at a higher nominal payload, only to discover it delivers less at their required extension. That mismatch wastes time on both sides.
Include three figures in your listing: the nominal payload, the reach at which that payload is rated, and the payload at maximum reach. Those three numbers let a reasonably informed buyer pre-qualify the machine before contacting you. Add the mounting orientations the manufacturer supports, and note the controller generation if you know it—controller compatibility affects whether a buyer's existing programming environment will integrate without additional cost.
If your team is building out a cobot section of your inventory, the compare tool on EasiMachines lets you place listings side by side so buyers can cross-reference payload, reach and other documented specs without requesting individual data sheets from you. That reduces back-and-forth on straightforward specification questions and lets the conversation move to application fit and pricing.
Information to confirm before listing or purchasing a used cobot| Specification item | Where to find it | Why it matters |
|---|
| Nominal payload (kg) | Manufacturer's product data sheet | Sets the upper capacity ceiling under rated conditions |
| Payload at maximum reach (kg) | Manufacturer's payload-reach curve or table | The real limit for tasks at the outer edge of the envelope |
| Maximum reach (mm) | Manufacturer's product data sheet | Defines the outermost boundary of the working sphere |
| Supported mounting orientations | Manufacturer's installation manual | Some models have reduced payload or restricted reach when inverted or side-mounted |
| End-of-arm tooling mass (kg) | Tool data sheet or direct weighing | Tooling mass reduces available payload for the part |
| Controller model and software version | Controller label or system info screen | Affects program compatibility and available safety functions |
Where used cobots sit differently from new ones in this specification conversation
With a new cobot, the buyer has access to the full specification document and factory support. With a used machine, gaps can appear: a missing data sheet for a discontinued model revision, an older controller that limits available functions, or a payload-reach curve published for an earlier software version that differs from what the machine is actually running. These gaps rarely make the machine unusable, but they shift more of the verification burden onto the dealer and the buyer.
For a used machine, pull the controller's system information screen before you list it. Note the software version and compare it against the manufacturer's current release notes. Older firmware may limit safety function availability or connectivity options that the buyer's integration team will expect. This is not a reason to avoid used cobots—the savings can be substantial—but it is a detail that should appear in your listing or your pre-sale conversation, not emerge as a surprise during commissioning.
A directional valuation on EasiMachines can give you a reference price range for a used cobot based on the details you enter, though it will decline when market evidence is thin for a specific model and age. Use it as a starting reference, not a final price—condition, controller generation, remaining warranty and included tooling all move the number.
Request a trial or simulation for mission-critical applications
If a buyer's application sits near the payload or reach limit of the machine, recommend an on-site trial or an offline simulation before the sale is agreed. Most cobot manufacturers and system integrators can run a simulation from a task description. That step is far cheaper than a return after commissioning.
Your next step: match specification to application before the listing goes live
Pull the manufacturer's full data sheet for each cobot in your inventory. Record the payload at maximum reach, the supported mounting orientations and the controller version alongside the headline payload and reach. Present those figures in your listing so buyers can self-qualify. For buyers who approach you with an application in mind but no machine selected, run through the payload-reach check above before you recommend a unit.
Browse current cobot and industrial automation inventory on EasiMachines at /equipment?industry=industrial-automation-robotics, or visit the industrial automation and robotics industry hub for further reference material in this category.
Frequently asked questions
Is the payload rating affected by the speed the cobot is running at?
Yes, on some models. Some manufacturers document a reduced payload ceiling when the arm operates at its maximum speed setting. If your buyer is running a high-speed application, check whether the manufacturer's data sheet states payload at different speed percentages, and verify that the required load stays within the appropriate limit.
Can a cobot be software-limited to operate within a lower payload range?
Some controllers allow the operator to set a software-enforced payload limit, which can affect the speed and torque the arm applies during movement. This is a configuration setting, not a physical hardware modification. It does not change the mechanical load on the joints if an oversized tool is fitted, so the physical payload limit still applies. Any software configuration of this kind should be documented and retained with the machine's records.
What happens if a used cobot has no surviving payload-reach curve for its specific revision?
Contact the manufacturer's technical support team with the machine's serial number. Most manufacturers can retrieve the data sheet for a discontinued revision or confirm which published document applies. If the manufacturer cannot provide documentation, treat the machine's usable payload conservatively—assume the figures apply at a moderate reach distance rather than at maximum extension—and communicate that uncertainty to the buyer before purchase.
Does the cobot's repeatability specification change with age and use?
Repeatability—the arm's ability to return to the same position consistently—can degrade as joint bearings and gearboxes wear. On a well-maintained machine, degradation is gradual, but a cobot with high cycle counts and no service history may show measurable position drift. Ask for controller logs or service records, and if the application is precision-sensitive, request a repeatability test using the manufacturer's recommended procedure before agreeing on a price.
