Upper　extremity　rehabilitation　robots　have　become　crucial　in　stroke　rehabilitation　due　to　their　high　durability,　repeatability,　and　task-specific　capabilities.　A　significant　challenge　in　assessing　the　comfort　performance　of　these　robots　is　accurately　calculating　the　human-robot　interaction　forces.　In　this　study,　a　four-degree-of-freedom　(4-DOF)　upper　extremity　rehabilitation　robot　mechanism,　kinematically　compatible　with　the　human　upper　limb,　is　proposed.　Based　on　this　mechanism,　an　algorithm　for　estimating　human-robot　interaction　forces　is　developed　using　Newton-Euler　dynamics.　A　prototype　of　the　proposed　robot　is　constructed,　and　a　series　of　comparative　experiments　are　carried　out　to　validate　the　feasibility　of　the　proposed　force　estimation　approach.　The　results　indicate　that　the　proposed　method　reliably　predicts　interaction　forces　with　minimal　deviation　from　experimental　data,　demonstrating　its　potential　for　application　in　upper　limb　rehabilitation　robots.　This　work　provides　a　foundation　for　future　studies　focused　on　comfort　evaluation　and　optimization　of　rehabilitation　robots,　with　significant　practical　implications　for　improving　patient　rehabilitation　outcomes.