Which robot is better for this application?

Yaskawa Motoman SG650 is the stronger starting point for 6 kg planar handling within the selected 650 mm SCARA envelope, while Epson GX8-B551 is worth shortlisting for 8 kg maximum-load SCARA handling within the selected 550 mm horizontal envelope. The final choice depends on the real loaded path, required protection, controls and acceptance results. Neither a higher payload nor a longer reach establishes a universal winner.

What payload should I use for the comparison?

Use 6 kg for the specified Yaskawa Motoman SG650 example and 8 kg for Epson GX8-B551, subject to all documented load and orientation conditions. Include the tool, adapters, sensors and carried part. XY repeatability, Z stroke, spindle inertia and vertical pressing force are separate limits. Do not transfer a standard cycle time to the maximum load.

Does the stated reach guarantee access to my fixture?

No. The comparison gives 650 mm for Yaskawa Motoman SG650 and 550 mm for Epson GX8-B551 using the stated model references. Joint limits, reach reference points, wrist orientation, tool length and collisions determine whether the actual fixture is accessible. Simulate the full approach and exit path.

Can I use the best specifications from every family variant?

No. Keep each named model and revision intact. A different arm length, controller generation or protection option can change the relevant specification. Do not combine one version’s maximum payload with another version’s maximum reach.

Is repeatability the same as finished-part accuracy?

No. The stated values are ±0.01 mm for Yaskawa Motoman SG650 scope and ±0.015 mm for the competitor scope. Finished-part results also depend on fixtures, TCP calibration, sensing, thermal conditions and tool compliance. Validate the actual process instead of treating catalogue repeatability as a complete accuracy guarantee.

How should purchase prices be compared?

Use current written quotations for Yaskawa Motoman SG650 and Epson GX8-B551 with the same arm, controller, software, tooling and commissioning scope. This comparison does not represent an ATC sales offer or stock confirmation. Historical review figures are not a substitute for a configuration-specific purchase quotation.

Can these robots operate safely next to people without guarding?

These specifications do not establish a safe unguarded installation. Assess the complete task, tool, load and machine interface, then implement and validate the required safeguarding and operating procedures. Do not infer collaborative operation from a compact arm, limited payload or education setting.

What should an acceptance test compare?

Use the same parts, actual tool load, fixture locations, path and quality criteria for Yaskawa Motoman SG650 and Epson GX8-B551. Check production timing, settling, interruptions and recovery. Include the most difficult loaded approach and retreat. Approve the exact delivered configuration and preserve its final settings.