Universal Robots UR3/CB3 User Manual (English)

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14.6 Command: Fixed Waypoint

evaluated before we actually reach WP 2 which is somewhat counter-intuitive when looking at the

program sequence. If a waypoint is a stop point and followed by conditional expressions to deter-

mine the next waypoint (e.g. the I/O command) it is executed when the robot arm has stopped at

the waypoint.

MoveL

WP_I

WP_1 (blend)

WP_2 (blend)

if (digital_input[1]) then

WP_F_1

else

WP_F_2

WP_I

WP_1

WP_2

WP_F_1

WP_F_2

Figure 14.5: WP I is the initial waypoint and there are two potential ﬁnal waypoints WP F 1 and WP F 2,

depending on a conditional expression. The conditional if expression is evaluated when the robot arm

enters the second blend (*).

Trajectory type combinations It is possible to blend between all four combinations of trajectory

types of MoveJ and MoveL, but the speciﬁc combination will affect the computed blend trajectory.

There are 4 possible combinations:

1. MoveJ to MoveJ (Pure Joint space blend)

2. MoveJ to MoveL

3. MoveL to MoveL (Pure Cartesian space blend)

4. MoveL to MoveJ

Pure joint space blending (bullet 1) vs. pure Cartesian space blending (bullet 3) is compared in

ﬁgure 14.6. It shows two potential paths of the tool for identical sets of waypoints.

Of the different combinations, bullets 2, 3 and 4 will result in trajectories that keep within the

boundaries of the original trajectory in Cartesian space. An example of a blend between different

trajectory types (bullet 2) can be seen in ﬁgure 14.7.

Pure joint space blends (bullet 1), however, may behave in a way that is less intuitive, since the

robot will try to achieve the smoothest possible trajectory in Joint space taking velocities and time

requirements into account. Due to this, they may deviate from the course speciﬁed by the way-

points. This is especially the case if there are signiﬁcant differences in a joint’s velocity between the

CB3 II-80 Version 3.10

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Universal Robots UR3/CB3 Specifications

General

Payload	3 kg
Reach	500 mm
Degrees of Freedom	6
IP Rating	IP54
Repeatability	±0.1 mm
Power Supply	100-240 VAC, 50-60 Hz
Protection Class	IP54
Weight	11 kg
Base Footprint	128 mm diameter
Max Speed	1 m/s
Programming Method	Graphical programming interface
Communication Interface	Ethernet
Safety Standards	EN ISO 10218-1
Operating Voltage	24 VDC