Troubleshooting KUKA SCARA X

Troubleshooting KUKA SCARA X

The KUKA SCARA X series is a 4-axis SCARA robotic arm designed for small component handling, assembly, inspection, and loading/unloading scenarios, covering KR 6 R500 Z200 X、KR 6 R600 Z200 X、KR 6 R700 Z200 X、KR 10 R600 Z300 X、KR 10 R700 Z300 X、KR 10 R800 Z300 X  Waiting for the model. Unlike six axis articulated arms, the core of SCARA lies in fast positioning in the horizontal plane and Z-axis linear motion in the vertical direction. Therefore, on-site problems often focus on resonance, screw shaking, Z-axis limit, load inertia matching, abnormal stopping distance, and enable switch circuits. For engineers searching for solutions, what is really needed is a layered troubleshooting method: first look at the safety circuit, then look at the load and stop, then look at the machinery and screw, and finally look at the controller and periphery.

Product positioning and model coverage

KR SCARA X belongs to a 4-axis articulated arm robot. The robotic arm is mainly composed of a small arm, ball spline screw, large arm, base, wiring harness assembly, and electrical equipment. The controller adopts KR CS Box-2, and the teaching pendant is smartPAD touch. The rated load of this series is divided into two categories: KR 6 series has a rated load of 3 kg and a maximum load capacity of 6 kg; KR 10 series has a rated load of 5 kg and a maximum load capacity of 10 kg. The maximum range of motion ranges from 500 mm to 800 mm, and the Z-axis stroke is available in two types: 200 mm and 300 mm. All models have a protection level of IP20, are installed on the ground, and have a noise level below 75 dB (A).

The model coverage is as follows: KR 6 R500 Z200 X weighs about 17.3 kg, with a workspace volume of about 0.136 m ³ and a cycle time of about 0.38 s; KR 6 R600 Z200 X weighs about 18.25 kg, with a workspace of about 0.195 m ³ and a cycle time of about 0.39 s; KR 6 R700 Z200 X weighs about 18.9 kg, with a workspace of about 0.25 m ³ and a cycle time of about 0.40 s; KR 10 R600 Z300 X weighs about 26.8 kg, with a workspace of about 0.286 m ³ and a cycle time of about 0.41 s; KR 10 R700 Z300 X weighs about 27.7 kg, with a workspace of about 0.407 m ³ and a cycle time of about 0.43 s; KR 10 R800 Z300 00 X provides a larger horizontal arm span. In terms of repeatability accuracy, XY is ± 0.02 mm, Z is ± 0.01 mm, and R is ± 0.01 °. These parameters determine the advantages of SCARA in high-speed small item handling, and also determine that the load and inertia must be strictly checked.

Axis data and motion range

The motion range of KR 6 series axis 1 is ± 135 °, axis 2 is ± 150 °, axis 3 is -200 mm/0 mm, and axis 4 is ± 360 °. KR 10 series axis 1 is ± 132 °, axis 2 is ± 150 °, axis 3 is -300 mm/0 mm, and axis 4 is ± 360 °. In terms of speed, the KR 6 series axis 1 is about 414 °/s, axis 2 is about 720 °/s, axis 3 is about 1.1 m/s, and axis 4 is about 2000 °/s. The KR 10 series axis 1 is about 355 °/s, axis 2 is about 450 °/s, axis 3 is about 1.1 m/s, and axis 4 is about 2700 °/s. The zero calibration positions are usually axis 10 °, axis 20 °, axis 30 mm, and axis 40 °.

The Z-axis adopts a ball spline screw, and the insertion force is clearly limited: the KR 6 series shaft 3 has an insertion force of about 150 N, and the KR 10 series has an insertion force of about 200 N. If press fitting, insertion or compression is required in the process, it must be confirmed that the insertion force does not exceed the allowable value, otherwise it will accelerate the wear of the screw and spline, and even cause Z-axis positioning drift. The mechanical terminal stops of axis 1 and axis 2 are used to protect the machine, but after a collision, the robotic arm may not operate reliably and must be stopped and confirmed with KUKA.

Safety logic and personnel requirements

The safety chapter applies to the mechanical components of industrial robots. If mechanical components are used together with KUKA robot controllers, it is also necessary to refer to the safety chapter of the robot controller. Industrial robots belong to incomplete machinery and are only allowed to be put into operation after being integrated into a complete system, combined with other machinery to form a complete system, or equipped with all safety functions specified in the EU Machinery Directive. The system integrator must issue an EC conformity declaration, affix the CE mark, and prepare a system operation guide.

In terms of personnel, operators must receive training and only qualified personnel are allowed to operate the equipment. Staff must understand the type of work, specific content, and potential hazards. The system integrator is responsible for installation, connection, risk assessment, safety features, protective devices, and compliance statements. Operators must fulfill their regulatory obligations, provide regular training, and comply with personal protective equipment regulations.

Dangerous areas include work areas and stopping routes. The protective device must be located outside the danger zone. The robotic arm must be located inside the protective shed, and the controller supports safety door sensors, but does not directly support light curtains or intrusion sensors; If other devices are used, a risk assessment and verification must be conducted. The mechanical terminal stop is used to limit the range of the shaft and cannot continue to operate after a collision.

Emergency stop, enable switch, safety door, and external safety stop must remain effective. If the smartPAD touch is disconnected, its emergency stop device will fail, posing a risk of confusion between connected and disconnected devices. After disconnection, it must be immediately removed from the system and stored outside the line of sight and reach of personnel. The enable switch must undergo functional testing at least once every 12 months, and in specific circumstances, it must also be tested. The default password must be changed before being put into operation, and only authorized personnel should be informed.

External forces such as impact or collision may cause subtle damage, such as slow loss of motor power transmission, leading to accidental movement. It is necessary to check for dents, paint wear, and especially carefully inspect the motor and balance cylinder. If there is damage, the components must be replaced. The grounding wire and potential balancing wire must have sufficient rated value and be correctly connected, and the connecting cable must be correctly connected and locked.

Installation, transportation, and foundation

When transporting the robotic arm, it is necessary to follow the prescribed transport posture to avoid vibration and collision. It can be transported by forklift or manually. Before transportation, it should be confirmed that the robotic arm is in a stable posture and that the connecting cables and accessories will not interfere. When installing, first install the foundation fixing device, then install the mechanical arm, connect the connecting cable, and finally finish.

The foundation load varies depending on the model. For example, when the KR 6 R500 Z200 X is installed on the ground, the normal vertical force is about 282 N, with a maximum of 367 N; the normal horizontal force is about 581 N, with a maximum of 586 N; the normal tilt torque is about 190 Nm, with a maximum of 194 Nm; the normal shaft 1 torque is about 96 Nm, with a maximum of 126 Nm. The KR 6 R600 Z200 X has a normal vertical force of about 291 N, with a maximum of 376 N; a normal horizontal force of about 531 N, with a maximum of 538 N; a normal tilt torque of about 196 Nm, with a maximum of 200 Nm; and a normal shaft 1 torque of about 103 Nm, with a maximum of 122 Nm. 216 Nm; the normal torque of shaft 1 is about 108 Nm, with a maximum of 126 Nm. The KR 10 R600 Z300 X has a normal vertical force of about 419 N, with a maximum of 462 N; a normal horizontal force of about 863 N, with a maximum of 867 N; a normal tilt torque of about 289 Nm, with a maximum of 298 Nm; and a normal torque of about 237 Nm for shaft 1 Nm， Maximum 294 Nm. When determining the size of the foundation, the maximum load must be followed and not just the rated value.

The connecting cables include motor cables, data cables, and grounding wires. Motor cables and data cables should be laid separately to avoid interference. The grounding wire must be reliably connected. The installation of user cables should be carried out according to the interface definition to avoid communication abnormalities or safety circuit failures caused by incorrect wiring. The controller and robotic arm must be matched, and the robotic arm cannot be connected to another mismatched controller.

Load, flange, and stopping distance

In terms of load, the center of gravity of all loads is related to the distance between the flange surface of axis 4. The load diagram shows the allowable loads for different Lxy and Lz. The rated load of KR 6 series is 3 kg, with a maximum of 6 kg; the rated load of KR 10 series is 5 kg, with a maximum of 10 kg. The maximum mass moment of inertia of flange Iz is 0.12 kgm ² for KR 6 and 0.3 kgm ² for KR 10; Rated mass moment of inertia: KR 6 is 0.01 kgm ², KR 10 is 0.02 kgm ². Exceeding the maximum load capacity will reduce the lifespan of the robotic arm and overload the motor and gears. Each time, it is necessary to check the load capacity and mass moment of inertia values, and ensure that the load data has been input into the robot controller. To reduce vibration, the center of gravity shift should be minimized as much as possible when installing end loads.

In terms of flange load, there are clear limitations on axial force, radial force, tilt moment, and torque during operation and emergency stop. Tool design errors may lead to breakage and loss of function, and it is necessary to calculate the tool for each individual situation based on load data and use the prescribed installation equipment. Additional loads can be installed on the support below the forearm, but attention must be paid to the maximum load; Increasing additional load may lower the tempo.

The stopping distance and stopping time are given by model. Stop category 0, immediately turn off the drive and apply the brake; Stop category 1 is to stop along the original path at the shortest distance, then disable the drive and activate short-circuit braking and motor braking; Stop category 2: Drive does not turn off, brake does not brake, brake along the trajectory slope. The triggering of safety stop includes emergency stop, safety input, control failure, violation of work area, and programming trigger. The stopping distance is part of the danger zone and must be included in the safety protection design.

Manual movement, simulation, and automatic operation

Manual operation mode is used for debugging work, including jogging, teaching, programming, and program verification. T1 is a manual slow mode with a speed not exceeding 250 mm/s, suitable for testing, programming, and teaching. T2 is a manual fast mode that allows for speeds greater than 250 mm/s and is only used for testing operations. When manually moving axis 1 and axis 2, follow the instructions on the controller; When manually moving axis 3 and axis 4, attention should be paid to the safety of the Z-axis and rotation axis. New or modified programs must be tested under T1 first. Tools, robotic arms, or additional shafts must not touch or extend beyond the barrier. Debugging work should be carried out outside the protected area as much as possible. If it must be carried out within a protected area, personnel must be equipped with confirmation devices, visible to each other, and maintain a gap of at least 50 cm, as determined by risk assessment.

The simulation program does not fully match reality. The program created in the simulation must be tested in a real system under T1 and may need to be modified. Automatic operation is only allowed when all protective devices are installed and functioning properly, there are no personnel in the hazardous area, and the prescribed workflow is followed. If the reason for the shutdown of the robotic arm is unknown, an emergency stop must be triggered before entering the danger zone.

Maintenance and Repair

After maintenance and repair, safety requirements must be checked and all safety functions tested. Maintenance must be carried out outside the hazardous area; If it is necessary to be in a hazardous area, additional safety measures must be taken. Industrial robots must be turned off and prevented from restarting, such as padlocks. If it is necessary to work while the controller is turned on, it is only allowed to work in T1 mode and additional safety measures should be taken. The emergency stop device must remain activated. If the safety function or protective device is disabled, it must be immediately reactivated after the operation is completed.

Before working with live parts, the power supply must be disconnected. Triggering an emergency stop or safety stop is not sufficient to ensure safety, as the components are still energized. The main switch must be turned off and prevented from being reconnected. For controllers without a main switch, turn off the device switch, disconnect the power cord, and secure it. Then check that the system has been powered off. Within a few minutes after the controller is turned off, there may be voltages exceeding 50V or even 780V in the components, and it is strictly prohibited to work during this period. The controller with a transformer must first turn off the transformer. Water and dust must be prevented from entering the controller. ESD regulations must be followed. Dangerous goods handling should avoid long-term skin contact, avoid inhaling oil mist, and pay attention to skin cleaning and care. The latest security data page must be used.

The maintenance schedule is executed periodically. Although the document does not provide a complete table, it usually includes screw lubrication, spline inspection, cable wear, fan cleaning, battery replacement, limit inspection, brake testing, etc. During maintenance, only new parts with the same part number or external parts approved by the manufacturer are allowed to be used. Clean and maintain according to the operating instructions.

Common troubleshooting

Resonance and screw shaking: Due to insufficient rigidity of the installation platform, large inertia of the end load, and specific angles and velocities, resonance may occur. When the end load is large, the arm is close to being extended, and the screw stroke is long, it is necessary to carefully evaluate the impact of end shaking and lifespan under high-speed motion. You can try changing the robot's movement speed, adjusting the teaching point position, and changing the load mass and inertia of the end fixture. If it is ineffective, contact KUKA support.

Z-axis positioning drift: Check the wear of the ball spline screw, whether the insertion force exceeds the limit, whether the load center of gravity is too large, and whether the Z-axis limit collides. Insertion force KR 6 is about 150 N, KR 10 is about 200 N, exceeding it will accelerate wear.

Axis 1/Axis 2 limit alarm: Check the mechanical terminal stop, software limit, zero calibration, and cable interference. After the collision terminal stops, the machine must be stopped and KUKA must be contacted.

Emergency stop cannot be reset: Check the smartPAD touch connection, emergency stop circuit, X11 safety interface, safety door, enable switch, and controller safety configuration. If smartPAD is disconnected, an external emergency stop must be used.

Enable switch failure: Enable switches must undergo functional testing every 12 months. If there is no response when pressed, check the connector, cable, and switch body, and replace the smartPAD touch if necessary.

Safety door triggers shutdown: check the operation safety signal, safety door switch, and confirm button. Automatic operation cannot be restored solely by closing the door, it must be reset by a confirmation device.

Overload caused by load: Check whether the load data is input into the controller, whether Lxy and Lz exceed the load map, and whether the mass moment of inertia exceeds the limit. It must be verified using KUKA. Load.

Flange tool fracture: Check whether the tool calculation, installation equipment, and flange load exceed the limit. The tool must be able to continuously withstand operating forces and torques.

Abnormal stopping distance: Check the brake, load, speed, and stopping category configuration. The stopping distance is part of the danger zone and must be verified regularly.

Communication abnormality: Check motor cables, data cables, grounding wires, shielding, and separate laying. The controller and robotic arm must be matched.

Condensation damage: If there is a large difference between the temperature inside the cabinet and the ambient temperature, wait for the temperature to balance before turning on the machine.

External damage: Check for dents, paint wear, and motor power transmission. After collision, the motor and balance cylinder must be checked, and damaged components must be replaced.

Battery/power outage issue: If the controller loses power, the battery maintains position data storage and is controlled to shut down. Check the battery charging status and load test.

Fan/temperature issue: Clean the fan and grille, check if the ambient temperature is within the range of 0-45 ° C.

Zero point loss: recalibrate axis 1 to axis 4.

Standards and Compliance

KR SCARA X involves mechanical instructions, EMC instructions, low voltage instructions, as well as standards such as EN 60204-1, EN ISO 10218-1, EN ISO 12100, EN ISO 13849, EN ISO 13850, etc. The robot system must be integrated into a complete system that complies with CE certification. System integrators must conduct risk assessments, implement safety functions, issue EC conformity declarations, affix CE marks, and prepare operational guidelines. If medical device manufacturers integrate SCARA into medical devices, they also need to consider relevant requirements such as IEC 60601-1. Industrial robots are incomplete machinery and are not allowed to be put into operation before integration.