XY gantry system: ball-screw and belt Cartesian positioning module

01

Choose the ball-screw accuracy grade for the stroke

THK states that ball-screw lead accuracy is controlled under JIS B 1192 (ISO 3408): grades C0 to C5 are defined by representative travel distance error and fluctuation over the thread length, and C7 to C10 by travel distance error relative to 300 mm. Its rolled ball-screw allowances are ±50 µm/300 mm for C7, ±100 µm/300 mm for C8 and ±210 µm/300 mm for C10; THK lists grades 0, 1, 3 and 5 for positioning screws and 0, 1, 3, 5, 7 and 10 for transport screws. [1]

MISUMI's selection notes give the same C5 values (25 µm mean travel error, 20 µm variation for 315–400 mm), variation per 300 mm of 8 µm for C3 and 18 µm for C5, and 52 µm and 210 µm per 300 mm for its Ct7 and Ct10 transport screws. It says the grade is chosen by checking whether the screw's mean travel error is within the allowable positioning error. [2]

Editorial calculation: if a C7 rolled screw's ±50 µm allowance applied to each successive 300 mm, a 600 mm stroke could carry up to ±100 µm and a 1,200 mm stroke up to ±200 µm of lead error; a C10 screw over 1,200 mm could reach ±840 µm. Linear accumulation is a worst-case assumption; ask for a measured lead-error chart. [1]

Give the supplier the X and Y strokes, payload and its centre of gravity, required positioning accuracy and repeatability at the tool point, maximum speed and acceleration, cycle pattern (one-direction or reversing), mounting orientation, cantilever length of the tool, and the controller or signals you will use.

02

Decide between belt and ball-screw drive, and handle backlash

NUODUN's XY Cartesian robot page lists X/Y travel strokes of 600–1,250 mm depending on load, repeatability of ±0.01 to ±0.05 mm depending on drive type, speed up to 1,000 mm/s and payload up to 65 kg, and recommends that cantilever extension not exceed 400 mm. It describes belt drives as faster and lower cost for light tasks, and ball screws as giving higher precision and load capacity. [3]

MISUMI notes that axial clearance in the screw does not affect positioning accuracy if feed is in one direction, but produces backlash and degrades positioning accuracy when the direction or the axial load reverses, so clearance must be chosen against the accuracy requirement. Its procedure also asks buyers to check axial load, allowable rotational speed and life, then shaft rigidity and temperature effects when higher accuracy or response is needed. [2]

Editorial calculation: at 1,000 mm/s a ball screw with a 20 mm lead turns at 1,000 ÷ 20 × 60 = 3,000 rpm, and with a 10 mm lead at 6,000 rpm; check either against the screw's allowable rotational speed at the full stroke length before accepting a quoted top speed. Leads are assumed examples. [3] [2]

03

Two-axis robots built from enclosed ball-screw or belt-driven actuators

The listing reviewed offers two-axis robots built from enclosed or semi-enclosed ball-screw actuators and belt-driven actuators, with stroke, speed and payload set per configuration.

04

Ball screw and nut, timing belt, linear guides, servo motors, beam and cable carriers

05

Stroke, cantilever, speed, payload and screw grade for an XY Cartesian module

Positioning accuracy is bounded by the screw grade: a rolled C7 screw allows ±50 µm per 300 mm of travel, so state the accuracy you need over the full stroke. [1]

06

Send the stroke, load and accuracy data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Strokes: [X; Y; Z if any]
Load: [payload; centre of gravity; cantilever]
Motion: [speed; acceleration; reversing or one-way]
Accuracy: [positioning; repeatability; measured where]
Drive: [belt or screw per axis; motor type; controller]
Site: [orientation; environment; supply]

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