Gantry Robot Device Module

Orthoganality Compensation Feature for Device Modules

Most linear-axis robots have two or more perpendicular (or orthogonal) axes. For example, with an X/Y robot the X-axis is assumed to be perpendicular to the Y axis. While the control system assumes that the axes are perpendicular (90° apart), actual systems often have some amount of orthoganality (or angular) error between the axes. That is, the axes are not precisely 90° apart.

This angular error is typically so small when compared to the relative precision required by the application that it can be ignored. Some applications, however, require such precision that this error is detrimental to machine performance. Correcting this angular error with hardware becomes very difficult and expensive. A more practical approach is to make corrections using software. With Adept's orthoganality compensation feature, a coupling matrix in the software is used to provide compensation.

To use the Orthoganality Compensation feature, you need to measure the error and configure the system software based on that error. (For details, see Configuration Instructions.) This configuration allows V+ to calculate the corrected position for each point on the the motion path regardless of whether the motion is commanded by program control or by the Manual Control Pendant (MCP). The system trajectory generator applies this correction automatically. (The default trajectory generation interval is 16ms.) Because this correction is applied automatically, there are no adverse side effects experienced during runtime operation.

Device Module Support

This feature is supported by the following robot device modules:

Cartesian Robot (CAR, ID 22)1

Enhanced LMMV XYZ-Theta Robot (ELM, ID 32)1

XY-3Z-Theta Robot (XY3, ID 21)2

Enhanced 5/6 Axis Gantry Robot (EGN, ID 19)2

For more details on the device modules, see the Device Module Document Menu.

Configuration Instructions

To use the orthoganality compensation feature, complete the following steps:

Measure the amount of angular error between the two axes.

Calculate the Encoder Scale Factors.

Enter results in the SPEC utility program.

Measure the Error

The amount of angular error between axes must be measured precisely.

Using a fixture known to be a square, align the fixture with one axis.

Measure the offset from the other axis.

Compute the angle of the offset.

This process is similar to measuring the perpendicularity of a Coordinate Measuring Machine (CMM).

The following figure illustrates angular error measurement. In Example 1, the angular error is 0 because the axes are exactly 90° apart. In this case, the Orthogonality Compensation feature is not needed. In Example 2 and 3, T represents the angular error as a signed value measured with respect to an expected 90° angle from the X- to Y-axes. For example, if the angle between X and Y is 85°, T = -5. If the angle between X and Y is 92°, T = 2. After measuring the error, use the value to calculate the Encoder Scale Factor.

Calculate the Encoder Scale Factors

If the angular error between axes is non-zero, calculate the encoder scale factors using the following formulas.

Joint 1 to motor 1 scale factor = S1

Joint 2 to motor 1 scale factor = S1 * tangent(T)

Joint 1 to motor 2 scale factor = 0

Joint 2 to motor 2 scale factor = S2 / cosine(T)

where S1 and S2 are the encoder scale factors specified in encoder counts per mm of joint motion.

For details, see the Adept SmartMotion Developer's Guide (for Adept SmartController-based systems). For Adept MV-Controller based systems, see the AdeptMotion VME Developer's Guide.

Enter the Encoder Scale Factor Results in the SPEC Utility Program

For SmartController-based systems, enter the encoder scale factor results using the Encoder Specifications menu in the SPEC utility program. For details, see the Adept SmartMotion Developer's Guide.

For MV Controller-based systems, enter the encoder scale factor results using the Edit Amp/Encoder Specs menu in the SPEC utility program. For details, see the AdeptMotion VME Developers Guide.

1Use of the CAR and ELM device modules requires the Kinematic Modules license (09961-00004).
2Use of the XY3 and EGN device modules requires the Enhanced Kinematic Modules license (09961-00007).