XYZ positioning stage

01

Read how accuracy and repeatability were measured

Novanta defines accuracy as the difference between the position commanded by the controller and the load position measured by an independent instrument such as a laser interferometer, and notes that accuracy varies along the travel because of machining, mounting and encoder errors. Averaging scattered measurements, as with RMS or 3-sigma methods, can make a datasheet figure look better than the stage performs; Novanta follows ISO 230-2:2006, which requires 20 target points plus the home position over the full travel. [1]

Repeatability is the ability to return to a commanded position. Novanta says unidirectional repeatability figures are better than bidirectional ones, that buyers should ask which is quoted, and that “typical” values may come from controlled tests rather than ordinary installation. [1] Dover Motion likewise notes that bidirectional variance is higher and that quoting unidirectional repeatability alone can mask large backlash; it measures with a laser interferometer over repeated approaches from both directions. [2]

Editorial note: for a stacked XYZ stage, ask for accuracy and bidirectional repeatability of each axis and, if the process depends on it, of the combined tool point, measured on stages taken from stock and mounted as you will mount them.

Give the supplier the travel on each axis, load and its centre of gravity, required accuracy and bidirectional repeatability, speed and acceleration, cycle (points per minute), mounting surface and orientation, environment (temperature, dust), controller interface, cable management and safety requirements.

02

Size speed and resolution from the drive

Dover Motion explains that leadscrew-driven stages generate frictional heating, causing thermal expansion and positional drift that depends on speed and duty cycle, and that where very high repeatability is needed a linear motor with a linear encoder in closed loop removes leadscrew effects, limited then by encoder resolution and thermal effects. From laser interferometer testing it reports its anti-backlash leadscrew stages at below 0.5 µm unidirectional and below 1 µm bidirectional repeatability (typ.). [2]

Editorial calculation: a ball screw with 10 mm lead turned at 3,000 rpm moves the carriage 10 × 3,000 / 60 = 500 mm/s; with a motor encoder of 10,000 counts per revolution, one count is 10 mm / 10,000 = 1 µm of travel, before screw lead error, backlash and thermal growth. Halving the lead to 5 mm doubles resolution and thrust per torque but halves top speed. Lead, speed and encoder counts are assumed examples; use the stage maker's figures and your load.

03

Read a full stage specification line by line

ALIO Industries' specification for its AI-XBS-10000-UII 100 mm ball-screw linear stage shows the set of figures a buyer can ask any supplier for. It is driven by a frameless torque motor and precision ball screw with an anti-backlash nut, with a non-contact optical linear encoder and dual recirculating ball rail bearings. Footnotes on the sheet tie performance values to stated conditions. [3]

The sheet lists accuracy, repeatability, straightness, flatness and angular errors separately, and gives the bidirectional (not only unidirectional) repeatability, which is what the measurement guidance above asks buyers to check. [3] [1] [2]

Editorial calculation: ±12 arc-sec of pitch over a 100 mm offset from the stage (Abbe arm) is 100 mm × 12 / 206,265 ≈ 5.8 µm of potential error at the tool point, larger than the ±2 µm accuracy of the upgraded grade.

Ask each supplier for the same lines: travel, accuracy and repeatability (bidirectional, with test method), backlash, resolution, straightness, flatness, pitch/yaw/roll, speed, acceleration, payload by orientation and environment.

04

Check how payload falls when a Z axis is stacked

Zaber Technologies lists its XY and XYZ systems as families built from its own linear stages, each with a maximum travel, a payload for the XY configuration, a lower payload for the XYZ configuration and a maximum speed. Families range from screw-driven compact and steel-bodied stages to direct-drive linear-motor stages, with linear encoder or dust cover options on some. [4]

Editorial calculation: the XYZ payload is 20% of the XY payload for the LSQ and LRQ families (10 kg of 50 kg), 5% for the LRM (2.5 kg of 50 kg) and 75% for the LRT (120 kg of 160 kg), so a vertical axis can set the load limit of the whole stage. The LDA and LDM linear-motor families list Z travel of 25 mm and 60 mm against 150 mm and 210 mm in X and Y. [4]

Give the supplier the payload mass and centre of gravity on the top axis, whether the Z axis lifts it, the travel on each axis and the speed needed, and ask which payload figure (XY or XYZ) its quotation is based on. [4]

05

XY tables and XYZ stages from ball-screw, belt and linear-motor modules

The listing reviewed covers XY tables and XYZ stages built from ball-screw and belt-driven linear modules, with linear motor modules and motion controllers. Ask for each axis's accuracy and bidirectional repeatability, test method and load rating.

06

Linear guides, ball screw or linear motor, motors, encoders, controller and cable carriers

Drift starts in the drive row: Dover Motion attributes it to frictional heating of the leadscrew and removes it with a linear motor and linear encoder in closed loop. [2]

07

Travel per axis, measured accuracy, bidirectional repeatability, speed and payload for a stage order

Ask for accuracy with its method (ISO 230-2, 20 points plus home) and repeatability as a bidirectional figure; Z travel, load capacity, motor type, humidity, IP rating, supply and weight have no published value in this table. [1]

08

Send the motion, load and accuracy data together

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

Travel: [X; Y; Z]
Load: [mass; centre of gravity; orientation]
Accuracy: [per axis; at tool point]
Repeatability: [bidirectional]
Speed: [speed; acceleration; points per minute]
Environment: [temperature; dust]
Control: [controller; interface]
Test data: [method; number of points]

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