MLX300: Understanding How to Use Teach Point Data Stored in the PLC

When a robot position is taught, the following data is stored:

• TCP data
• Axis (joint) data
• Closure  
• Robot Number that taught the point
• User Frame Number   (“-1” means it’s a world position)
• Tool Number   (“-1” means a tool is not activated)

TARGET TYPE

All MLX300 Linear and Axis motion commands include a TargetType parameter which defines which data will be used for the teach point motion.   

• TargetType = 0     - use teach point axis data
• TargetType = 1     - use teach point TCP data

When you teach a point from the HMI or MLX Teach Screen on the pendant, both the axis data and TCP data correspond to the same robot position.  

Caution should be taken when the PLC automatically calculates teach point TCP data.    For this case, the TCP data and Axis data will not be the same.   In order to command a motion to this position, the TargetType must be set to “1”.

It’s recommended to use TargetType = 1 (TCP) for most move commands.   However, the TCP position could have different robot pose orientations.   If you need to force the robot to the exact pose the robot was in when the point was taught, use the TargeType = 0 (axis).   For axis data, there is only one pose position.

ROBOT NUMBER

A new MLX300 feature is that when a point is taught on the HMI or MLX Teach Screen, the robot number or external axis number is also stored.   This is very beneficial when there are multiple robots to determine which robot this point was taught for.   Note that all robots can use any point taught, but in most cases, the points are taught for a specific robot number.  

An example of this benefit is shown below.   On the left figure, robot 2 is active for jogging, but the selected point 0 was taught with robot 1.  There’s a warning to advice changing the jogging device to robot 1.   On the right figure, the selected point 3 was taught for external axis 1, and there’s a warning to advice changing the jogging device to external axis 1.  

TOOL NUMBER and USER FRAME NUMBER

When a point is taught, the tool number and user frame number that is currently active will also be stored.    This is just reference information on how the point was taught.   Changing this information will not change the position, so it should never be altered.    The information is useful for commanding motion or jogging back to this point.    The correct tool and user frame number must be always be active before the motion is initiated.   If these items are not the same, the robot will move to a different position.  

Note that if the Tool Number is “-1”, this means a tool is not active.    It’s highly advised to always set a tool number active during a startup routine before commanding motion.    Having an active tool will create faster motion.  When the power is cycled, the active tool and active user frame both get set to “-1”.

If the User Frame number is “-1”, this means that the Coordinate Type was set to World or Base when the point was taught.   Having an active user frame number when a motion is commanded to this position will not affect the position.    It will always move to the world position that was taught.

If the User Frame number is a positive number, this means the Coordinate Type was set to a User Frame Number when the point was taught.   To command motion to this point, the active user frame number must be set to this number.    If you want to move the robot to this point in reference to another user frame, all you need to do is set the active user frame to the desired number before commanding the motion.

CLOSURE

When a robot is commanded to a TCP position, it could choose one of multiple robot poses to achieve this point.   Refer to the picture below.    These robots are at the same TCP position.

The MLX300 includes Closure data for each axis to force the robot into a certain pose.   Most of the time this is used for the T-axis to prevent a rotation that will damage cables or interfere with other hardware. 

The closure data is defaulted to all “0s”, which means the robot will take the shortest motion to achieve the TCP position.    If the motion will interfere with an axis limit, the motion will be executed in the opposite direction.  

To force an axis a certain direction, closure data can be changed.    The way this is defined is shown below:

• When the Closure is between -180 and +180, the axis will be forced to move one direction
• When the Closure is less than -180 and +180, the axis will be forced to move the opposite direction.

For example, if you set the T-axis closure to 100 it will move one direction, and if you set it to 200 it will move in the opposite direction.  The actual direction (CW or CCW) depends on the axis being moved, the

angle it's moving from and the angle it's moving to.   The best procedure for setting up the closure is to try a closure value of 100 first at a slow speed.  If the motion direction is not correct, change the closure value to 200.