Accurate zero point correction not only ensures the consistency of the robot program trajectory, but also guarantees the absolute accuracy of positioning accurate robots or high-precision robots.
Precise positioning robots require high zero point correction accuracy to guarantee absolute accuracy.
The robot sets the angle of each axis. The zero angle of each axis is determined by the variable $MAMES[]. (Automatic completion of the robot system)
Figure: According to the position of the zero point probe and the marking slot, the angle of different models of robots is not the same.
Record the current motor angle of the correction zero. (Robot system auto-complete)
The motor angle value will be stored in a background file, e.g. "653631.cal" (file name is robot serial number)
Special tips
● Zero correction requires the help of a tool dial or KUKA EMD
KUKA EMD
Dial-up table
Note: The dial gauge correction zero error is relatively large. Factors such as personnel measurement error and needle sensitivity will affect the accuracy of the zero correction. This method is not recommended when the program trajectory requirements are high (such as arc welding, flanging, etc.).
● Some models of robot A6 axis are not equipped with a zero point probe, and when correcting the zero point, it is necessary to align the notch line and use the "reference method" to correct the zero.
Zero correction requires the help of a tool dial gauge or KUKA EMD, as well as two different methods of zero point correction, standard and loaded.
We move from theory to practice
Specifically, how to do it with KUKA EMD
Method of EMD zero point correction (standard)
❶ Runs all axes of the robot to the "pre-corrected" position
Explanation of terms: Pre-corrected bit
The "pre-corrected" reference idiosyncrasies are usually grooves or pits, and are painted in white paint. Operate the robot, align the identities, that is, the pre-corrected position.
❷ Install the EMD sequentially on the zero point probe of the corresponding shaft
(Note: When the EMD is installed in the probe, you cannot manually move the shaft.) Failure to do so will damage the probe. ）
Go to the menu "Perform zero correction"
Select the axis to which you want to zero and click the "Correct" button.
Wait 2 seconds and press and hold to power up the servo.
As shown above, there are 3 enable keys behind the teach pendant.
Press and hold the start key again and hold, and the robot axis will move slowly to find the zero mark slot.
❼ The robot will automatically stop when completed, and then release the enable and start keys.
● Repeat steps 2-7 in turn to complete the zero point correction for each axis.
The above is the method of EMD correction of the zero point of the standard (i.e. single load specification).
For single loads (standard) we recommend carrying a load correction with the first correction and the same load with each subsequent correction.
How a loaded robot performs zero correction
Effect of load gravity on zero correction
When the robot is loaded with tools and other loads, due to the weak rigidity of the reducer and the gap of the gear transmission, the robot shaft will sink under the action of gravity.
Therefore, the load affects the zero correction of the robot.
So, how does the load handle during zero correction?
Do I need to disassemble beforehand?
How is the load handled during zero correction?
When adjusting at zero point, it is not necessary or recommended to remove the load tool; otherwise, TCP may have to be recalibrated after disassembling the tool.
In practice, the zero point correction work can be carried out after the robot tool is installed. However, when re-correcting or checking the zero point later, this tool needs to be loaded. If the tool is removed, the robot is less stressed, the shaft will bounce back, and the zero point will be different from when the tool is loaded.
Therefore, the robot load state needs to be consistent during zero correction.
For example:
A robot is used for the first time when it is no-load correction, then it needs to remain empty when it is corrected at zero point;
Robot B is used for the first time with a tool to correct zeros, and this tool needs to be installed when correcting the zero point in the future.
Questions
C robots use three tools of different weights when working: Tool1, Tool2, Tool3, how to operate when the zero point correction?
Reply
At this point, the no-load zero correction can achieve the desired purpose, but it is more troublesome in operation: the tool must be removed every time the zero point is re-corrected or checked, which increases the operator's workload.
To avoid the above troubles,
Load correction for easier operation
The zero-point correction scheme "with load correction" in the KUKA system cleverly solves the problem of the different weights of the three tools.
Procedure
❶ First, the robot remains unloaded and enters the "First Adjustment" function for zero correction. (If you have a lighter tool like a gun changer, you can also make a "first adjustment" after installation.) ）
❷ Install each tool in turn, go to "Bias Learning" separately, and click on each axis as prompted to "Learn". (Each tool needs to perform a bias study of 6 axes separately.) ）
After completing the above two steps, the zero point correction is completed. For details, please refer to the KUKA Micro School | Steps 1-7 in the second lesson.
Note: The "Absolute Accuracy Robot (Robot with PID File)" must use the no-load zero correction operation, or the "Load Correction" scheme with tools must be used for zero correction operation, otherwise its absolute accuracy will be affected.
Robots that perform zero point correction through the "Load Correction" scheme can load any tool after receiving the "training" of bias learning and enter the "Load Correction - with Bias" mode to re-zero or check the zero point when it is needed to re-correct the zero point or check the zero point in the later maintenance.
Precautions
1) When using the "biased" function to correct the zero point or check the zero point, the system will automatically reject the bias value generated by the gravity of the tool to ensure that it is consistent with the load state when the no load is zeroed.
2) "No bias" function, only applicable to the restoration of the original zero point correction value in the case of loss of zero point due to human error deletion or electrical reasons (such as RDC card failure, sudden power failure), and is not allowed to replace the motor, gearbox or mechanical disassembly.
Finally, send you a summary map of the method of EMD correction zero point, take it well!
"Configuration of Linear Units"
To be more practical, we will use "Configuring the Motion System with the KUKA KL-100" as an example.
KUKA KL-100 linear slide
The KUKA Linear Rail KL 100 is a stand-alone uniaxial linear slide rail mounted on the ground, ceiling or wall. It is widely used in handling, handling, plastics processing, testing or inspection.
The KL 100 operates as an additional axis for the robot and is suitable for all robots of the KR AGILUS series. As a result, control is carried out by the respective robot controller.
Without further ado, get to work
Configure the destination
The KR 6 R700 sixx robot from the KR AGILUS series is mounted on KUKA's KL-100 rail, and the ROBROOT motion system can be configured to enable synchronous control of the linear guide and the robot.
How? Look here!
Use WorkVisual to configure linear units, So easy↓↓↓
Step 1 Click File → Directory Management
Step 2 Select KukaExternalKinematics230V Click on a single arrow to add to the existing directory
Step 3 Right click Add → Project Structure
Step 4 Select KukaExternalKinematics230V → KL100 → Add
Step 5 KL100 is added to the project structure
Step 6 Fill in the parameters of the KL100 as shown in the figure on the right.
Step 7 Then download the project to the robot control cabinet
"Offset calibration of linear units"
Possible problems
Normal linear units do not require special calibration. In WorkVisual, configure the conversion value of the ROBROOT motion system.
However, sometimes when using the linear axis to test the external motion system, there may be a small change in the TCP position of the tool, and in some applications that require high accuracy of the program trajectory, it will not be able to meet customer requirements (such as swing applications, etc.).
Problem analysis
Ideally, the ROBOT's ROBROOT coordinate system should be the same as the FLANGE coordinate system for linear elements. In practice, installation errors often occur, resulting in slight differences between the two coordinate systems, which means that the position of TCP is skewed when using an external axis motion coordinate system. If KSS 8.3 is installed in the robot controller, these differences can be corrected by means of Offset calibration of the linear unit.
Next, let's get into the hands-on session
For specific calibration operations, we also use the KUKA KL‐100 configuration motion system for example.
Offset calibration of linear elements - calibration steps:
Step1 Click menu: Put into operation→ measure the linear slide → the external kinematic device →
Step2 Select the reference tool and click the button to continue.
Step3 Determine the direction of movement of the linear slide and click the button to continue.
Step4 Move the reference tool TCP to the reference point and click the button Measure.
Move the TCP of the measurement tool from 3 different external axis positions to the set reference point.
The robot control system calculates The Offer from three different positions.
Step5 In the pop-up window, click the button Yes.
Step6 Repeat steps 4-5 twice, and the measurement results in the following figure will appear, click the button to save.
It's also important to note that there are four things you want to make sure before you do it specifically:
1. The relevant external axis has been configured at WorkVisual to load it into the robot controller.
2. The previously calibrated tool is installed on the mounting flange.
3. No programs are opened or selected.
4. T1 mode