A dispensing "Node" is the most fundamental data element within the Guidance Dispense software. It defines a single syringe tip position and includes information about whether dispensing is turned on or off relative to this position. In order to specify the robot motion or action associated with a position, Nodes are organized into Node Types. For instance, there is a Node Type that indicates that the syringe tip is to move along a straight line to the position and a different Type to specify that a circular arc path is to be followed.
The following example illustrates a Path that contains four Nodes. Step 1 moves the syringe tip to a starting location. When this location is reached, dispensing is turned on. Next (Step 2), the tip is moved along a straight-line path to a location that serves as the end of the line and the start of an arc. Finally, the syringe is moved along an arc path (Steps 3 & 4), after which dispensing is turned off.
1. LineStrt -ON
2. LineEnd 3. ArcMid 4. ArcEnd -OFF
While GD could have been designed to define Node positions with respect to the base of the robot, instead, Node positions are always defined relative to a "reference frame". A reference frame specifies an important XYZ position and orientation that is significant to the dispensing application. For example, if you wish to dispense fluid on to a plate, the position and orientation of a corner of the plate could be defined by a reference frame. Then, instead of teaching positions relative to the base of the robot, each Node point would automatically be taught with respect to the corner of the plate. If the plate were later re-positioned or re-oriented, the positions of all of the taught points could be compensated by simply updating the position and orientation of the reference frame. This is illustrated in the following picture that depicts the four Node Path previously discussed.
To simplify the use of a reference frame, by default, all Node positions are relative to the Global Frame. A utility for quickly defining the position and orientation of this reference frame is included in the GD software. If the value of the Global Frame is not taught, it will have a NULL value and all Node positions will be with respect to the base of the robot.
If your system is equipped with PreciseVision, vision can dynamically compute and return a reference frame that replaces all of the coordinates of the Global Frame except for its Z height. In the example above, a camera could be used to locate the position and orientation of the corner of the plate. Then all of the taught Node positions would be automatically adjusted to reflect the plate position and orientation as determined by PreciseVision.
Since application requirements or fluid properties may require that dispensing be turned on at the start of a motion or at the end of a motion or somewhere in between, GD supports a number of means for specifying when dispensing signals should be turned on or off. Each Node can specify that a signal must be changed a fixed distance or time from either end of its motion or as a percentage of travel. By default, signals are changed at the end of each motion.
In the following table, each of the Node Types is described. For some types, like the Line Node, you simply specify that you want a Line Node. However, when the Node is subsequently displayed, the software automatically distinguishes whether a Line Node starts a sequence of straight-line motions, ends a sequence or is in the middle of a sequence. This extra qualification is provided as a visual aid in understanding what motions are to be performed.
Node Type |
Description |
|
Line |
Line Nodes define points between which the syringe tip will be moved along a straight-line path. A minimum of two Line Nodes are required to defined a line path, the "LineStart" and the "LineEnd". In addition, an arbitrary number of Line Nodes can be placed between these points and will be labeled "LineMid". |
|
Arc |
Arc Nodes define a circular
arc motion. An arc motion must start with a Line or
Pause Node followed by an arbitrary number of pairs of Arc
Nodes. The
minimum arc motion consists of a Line Node followed
by two Arc Nodes. Arc Nodes cannot
be placed after a Path Break or Dot. The
last Arc Node in a sequence is labeled the "ArcEnd" and
all of the intermediate points are labeled "ArcMid".
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|
Path Break |
If you wish to stop dispensing fluid
and start another dispensing sequence within a single Path,
as a programming convenience, you can insert a Path Break Node. This Node will
turn off dispensing, automatically move above the previous
Node position by an amount "mm
Above Path", and then
move to a position "mm Above Path" above the next Node position.
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|
Pause |
A Pause will stop the robot's motion at a Node for a specified period of time. This is useful to form a fill area that is along the Path. This Node can start or end a Path in order to delay before fluid is dispensed or to delay until after the dispensing completes. |
|
Dot |
A Dot Node dispenses a single dab of fluid at the Node position. The dispense tip is moved above the Node position by the Path's "Approach" height, moves down to the Node position and turns on dispensing, delays for a specified time, turns off dispensing, and then retracts to the Path's "Depart" height. This Node can start or end a Path. In fact, a Path could consist of several Dot Nodes and nothing else if required. |
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