KUKA KR C4 Smallsize-2 Debugging Guide

Practical Analysis of KUKA KR C4 Smallsize-2 Controller Assembly, Safety Debugging, and Troubleshooting

KUKA KR C4 smallsize-2 is a controller designed for small robots, compact workstations, and limited cabinet space. Compared to medium-sized controllers, it compresses the drive unit, control PC, CCU_SR, battery, safety interface, and cooling air duct into a cabinet weighing approximately 60 kg, and supports up to 6 servo axes. For engineers, the difficulty of smallsize-2 lies not in "multiple wiring", but in compact space, centralized interfaces, and tight coupling between the safety chain and the logic of the US2 load voltage. Once there is a deviation in the assembly sequence, equipotential, X11 safety interface, or WorkVisual configuration, the system may appear as unable to power on, unable to reset E-STOP, ineffective enable, T1 speed alarm, or inability to cancel safety stop. This article focuses on assembly, safety, interfaces, power on, module replacement, and troubleshooting, providing executable inspection paths.

System architecture: First distinguish KPP_SR, KSP_SR, KPC, and CCU_SR

The core of KR C4 smallsize-2 consists of a drive unit, control PC, Cabinet Control Unit Small Robot, low-voltage power supply, battery, bus equipment, and cooling system. The drive unit, also known as the Drive Configuration, contains KUKA Power Pack Small Robot and KUKA Servo Pack Small Robot internally. KPP_SR400 is responsible for generating intermediate circuit voltage, while KSP_SR is responsible for checking intermediate circuit voltage in motor control, brake control, and brake mode. The drive unit is not a simple power module, it simultaneously undertakes motor control, brake control, and intermediate circuit monitoring.

The control PC is responsible for graphic interface, program creation and modification, archiving and maintenance, sequence control, path planning, driver circuit control, monitoring, safety device communication, and external device communication. Control PC can install D3236-K or D3445-K motherboard. D3236-K provides X961 DC 24V power supply, X962 PC fan, slots 1 to 7 KUKA Controller Bus、KUKA System Bus、USB 2.0/3.0、DVI-I、KUKA Option Network Interface  Interface with KUKA Line. D3445-K provides interfaces such as DVI-D, Display Port, USB 3.0, etc. When an external monitor is required, the user interface can only be displayed on the external monitor if there are currently no active operating devices (smartPAD, VRP) connected to the controller.

CCU_SR is the central power distribution and communication interface, consisting of CIB_SR and Power Management Board. It is responsible for safety input and output, contactor activation, 4 floating outputs, 9 safety inputs, smartPAD insertion recognition mastering test、 6 fast measurement inputs, external fan monitoring, power fan monitoring, and cabinet temperature acquisition. Connect the driver unit through KUKA Controller Bus RDC、 Digital I/O module; Connect the operation panel, diagnostic LED, and EDS interface through KUKA System Bus. When the main power supply fails, the battery continues to supply power to the control components until the position data is saved and the controlled shutdown is completed. Before the first start-up, the X305 connector on CCU_SR must be plugged in to remove the battery discharge protection during transportation.

The bus is divided into KCB, KSB, and KEB. KCB equipment includes driver units, RDC, CIB_SR, and EMD. KSB devices include CIB_SR, SION, smartPAD, SION, and optional extension SIB. KEB is used for optional interface extensions. Understanding these three layers of buses can quickly determine whether the problem lies on the driver side, system side, or expansion side in the event of communication failure.

Installation conditions and power supply boundary: Small cabinets are more afraid of heat dissipation and spacing issues

KR C4 smallsize-2 has a maximum of 6 servo axes, weighs approximately 60 kg, has a protection level of IP54, and produces noise levels below 66 dB (A). The default color is RAL 7016 side panel and KUKA orange door. The cabinet top is uniformly loaded with 1500 N and installed side by side with a spacing of 50 mm. The controller is only supported from KSS ≥ V8.3.20 onwards, which must be confirmed during the upgrade of the old system.

In terms of power supply, the rated voltage is AC 3 × 380 V, 3 × 400 V, 3 × 440 V, or 3 × 480 V, requiring a grounded neutral point with an allowable deviation of ± 10%. The rated connection power is 3.30 kVA, the short-circuit current withstand capacity is 5 kA, and the system impedance is not greater than 300 m Ω. The main power supply side fuse is 3 × 32 A slow melting; When not equipped with a drive box, it is 3 × 16 A slow melting. The frequency range is 49 to 61 Hz. If there is no grounded neutral point on site or the voltage does not match the nameplate, a transformer must be used. The controller can only use a grounded neutral point power system, otherwise it may cause damage to the power unit and personal injury.

The environmental conditions are equally strict. The ambient temperature during operation is+5 to+45 ℃; The temperature range for storing and transporting batteries is -25 to+40 ℃, and for storing without batteries it is -25 to+70 ℃. The maximum temperature change is 1 K/min, and the environmental level is 3k3. There is no derating below an altitude of 1000 meters, and the derating is 5% per 1000 meters from 1000 to 4000 meters. If the controller is moved from a cold environment to a warm site, condensation may occur inside, and it must wait for the temperature inside the cabinet to balance with the environment before powering on. The battery maintenance cycle is executed according to the storage temperature: charging every 9 months at temperatures not exceeding+20 ℃, every 6 months at temperatures between+20 ℃ and+30 ℃, and every 3 months at temperatures between+30 ℃ and+40 ℃.

The cooling system is divided into two circuits. The inner area contains control and power electronics, cooled by a control PC fan; The outer area includes braking resistors, low-voltage power supplies, and drive unit heat sinks, which are directly cooled by ambient air introduced by an external fan. Do not install filter cotton in front of the ventilation opening, otherwise the temperature rise will shorten the service life of the equipment. During installation, it is necessary to maintain the minimum spacing and ensure that the maintenance channel can open the cabinet door.

Security Chain: Engineering Logic for X11, X13, X66 and STOP 0/1/2

The safety controller of smallsize-2 is located inside the control PC and is responsible for switching drivers, applying brakes, monitoring brake slopes, monitoring stillness, T1 speed monitoring, evaluating safety signals, and setting safety outputs. The safety functions include operation mode selection, operation safety, emergency stop device, enable device, external safety operation stop, external safety stop 1, external safety stop 2, and T1 speed monitoring. Installing flanges at a speed exceeding 250 mm/s under T1 will trigger a safety stop of 0.

Safe stop is divided into STOP 0, STOP 1, and STOP 2. STOP 0: The safety controller immediately cuts off the driving and braking power supply; STOP 1 is executed by the non safety part for braking, monitored by the safety controller, and the power supply for driving and braking is cut off after the robot stops; After STOP 2 braking, the driver remains activated, the brake is released, and it switches to safe operation stop monitoring. Understanding the differences between these three is crucial for determining "why cannot be reset" and "why drive enable is lost".

There are various safety interfaces: X11 parallel safety interface, X13 parallel safety Safe Robot, X66 Ethernet safety interface PROFIsafe/CIP Safety, X55/X67.1/X67.2 Ethernet safety interface FSoE. X11 is internally connected to CCU_SR. The X11 pins include CIB_SR test output A/B, safety operation stop channel A/B, safety stop 2 channel A/B, external E-STOP channel A/B, confirm operation safety channel A/B, operation safety channel A/B, Peri enabled output, and confirm operation safety output. The secure input adopts a dual channel design and cyclically detects the shutdown capability. The test output TA_S and TA_S are alternately turned off, with a turn off pulse length of about 625 μ s, a single channel turn off period of about 106 ms, and a two channel offset of about 53 ms. The input channel SIN_X_A must be powered by TA_S, and SIN_X_B must be powered by TA_S, and other power sources must not be used. Only sensors that can access test signals and provide floating contacts are allowed to be connected.

The external enable switch can be connected through X11. External enable 1 requires pressing when jogging under T1/T2, input to close; External Enable 2 requires the switch to not be in the panic position and the input to be closed. If connected to smartPAD, its enable switch performs AND logic with external enable. When external enable 1 is not connected, channel A's 11/12 and channel B's 29/30 must be short circuited; When external enable 2 is not connected, channel A's 13/14 and channel B's 31/32 must be short circuited.

Operation safety signals are used to monitor physical protections such as safety doors. Without this signal, it cannot operate in automatic mode; Opening the safety door during operation will trigger safety stop 1. When restoring, the safety gate must be closed and the dual channel confirmation button must be pressed outside the fence. This confirmation function is not activated by default and needs to be set in the security configuration. Automatic closure of safety doors cannot replace manual confirmation.

X20, X19, X21, and USS2: Wiring errors are more dangerous than parameter errors

The motor is connected through X20. X20 uses Harting Han Jellock monoblock size 30, with pin definitions including U1, V1, W1 from M1 to M6, 24V and GND for brake shafts 1 to 3, 24V and GND for brake shafts 4 to 6, and PE. Motor cables must be laid separately from data cables to avoid interference. The fixed installation bending radius is 3 to 5 times the cable diameter, and the drag chain installation is 7 to 10 times.

SmartPAD is connected via X19 and uses the Intercontinental series 615. X19 includes TD+, TD -, RD+, RD -, smartPAD insertion recognition, 24V PS2, and GND. If smartPAD is disconnected, the E-STOP on it is no longer valid, so the system must have at least one external E-STOP.

RDC is connected via X21 using Harting HAN3A/Q12. X21 provides+24 V, GND with battery backup,+24 V without battery backup, TD+, TD -, RD+, RD -. For the X21 US2 RDC interface, the US1 with battery backup is used to power the RDC, and the US2 voltage is switchable through safety technology. USS 2 is used to cut off actuators through Beckhoff plates or other means when the drive is disabled. There are three variants of US2: external PLC switching, KRC switching, and deactivation. If US1 and US2 are short circuited due to cross connection of system cables, they will not be detected during normal operation, and the result is that US2 cannot be turned off, which may cause a dangerous state. Therefore, US1 and US2 must be wired separately or reinforced with insulated cables.

The US2 function must be checked in the following situations: after initial startup or re debugging, after robot changes, after safety configuration changes, after software updates, and after replacement of load voltage contactors. In the automatic variant, press the enable switch, the contactor is engaged, and the robotic arm can move; Release the enable switch and disconnect the contactor. Under the external PLC variant, the "Peripheral contactor (US2)" input check in the PROFIsafe/CIP Safety telegram can be cancelled. Under the KRC variant, the operation safety device can be turned on in automatic or automatic external mode, or the enable switch can be released for inspection in T1/T2. If the USS 2 option is used, the USS 2 status signal must be checked before starting the peripheral device.

Equipotential, transportation, and power on: Small cabinets should also be treated as large systems

The equipotential connection includes a 4 mm ² cable between the robotic arm and the controller; An additional equipotential cable of 4 mm ² is recommended between the central PE row and the controller PE connection. If a drive box is installed on KR C4 smallsize-2, a 16 mm ² PE conductor must be used between the drive box and the workshop equipotential; No additional 4 mm ² cable is required between the controller and the workshop equipotential. Before powering on, check the automatic power-off protection conditions in section 18.2 of EN 60204-1.

During transportation, the controller must be powered off, have no cable connections, the cabinet door must be closed, and the cabinet must be upright. Use 4 M8 DIN 580 lifting rings and lifting frames to slowly lift, move, and lower. It can also be transported by pallet trucks. Casters are only used for rolling inside the cabinet row and cannot be transported over long distances, let alone towed by forklifts or electric vehicles. The transportation of casters requires a flat and unobstructed ground, otherwise there is a risk of tipping.

ESD regulations must be followed before powering on. The installation must be horizontal and maintain the minimum spacing. Check whether the transportation damage, insurance, contactors, and boards are tightened, whether the modules are loose, and whether the screws and clamping connections are reliable. The operator must cover the 'Read manual' warning label with a local language label. After connecting the motor cable, data cable, external shaft cable, and peripheral cable, plug in X305 and connect X1 power supply. If the system configuration changes, it must be reconfigured using WorkVisual. The startup mode can only be used when external safety devices have not been installed or put into operation, and warning tapes, fences, or signs must be set up to ensure that no one is in the danger zone.

Module replacement: Same type can be replaced, but different models must be reconfigured

If the replacement is KCB, KSB, or KEB equipment of the same type, it can be replaced. Any number of KCB, KSB, and KEB devices can be replaced until all devices are simultaneously replaced by devices of the same type. But it is not possible to exchange two identical KCB components at the same time, only one of them can be exchanged at the same time. If changing to a different model, adding or removing devices, replacing hard drives, or installing a new KSS, the WorkVisual configuration system must be used.

After replacing the data cable, it is necessary to re master or perform a mastering test, otherwise incorrect position data may cause unexpected movement. After replacing the safety module, it is necessary to check the safety configuration, checksum, and safety axis monitoring function. If the security configuration checksum changes, the safety axis monitoring function must be checked. After any security related modifications, functional testing should be conducted and the results recorded.

Common troubleshooting: Starting from the safety chain, power chain, and communication chain

Fault 1: The controller cannot be powered on. Check X1 power supply, main switch, fuse, CCU_SR power supply, X305 battery connector. If the control PC does not start, check the low-voltage power supply, motherboard, fan, and power button. If the main contactor does not engage, check whether the safety chain is closed, whether the E-STOP is released, and whether the X11 external E-STOP is consistent in both channels.

Fault 2: E-STOP cannot be reset. Check the smartPAD E-STOP, external E-STOP, X11 local/external E-STOP pins, dual channel status, safety door, and operational safety confirmation. If using Ethernet secure interface, check the PROFIsafe/CIP Safety/FSoe connection and input/output bytes. E-STOP not tested for more than 12 months may also affect the effectiveness of safety functions.

Fault 3: Loss of operation safety signal. Opening the safety door in automatic mode will trigger safety stop 1. When restoring, the safety gate must be closed and the dual channel confirmation button must be pressed outside the fence. The confirmation function may not be activated by default and needs to be set in the security configuration. Automatic closing of safety doors cannot replace manual confirmation.

Fault 4: The enable switch is invalid. The smartPAD enable switch has three positions: not pressed, middle position, and panic position. Only the middle position can be moved under T1/T2. If an external enable switch is connected, X11 pins 11/12, 29/30 and 13/14, 31/32 need to be wired correctly; Short circuit is required when not in use. Two enable switches should be kept in the middle position for no more than 15 seconds at the same time, otherwise a safety stop 1 will be triggered.

Fault 5: T1 speed monitoring alarm. Check program magnification, manual magnification, tool load, and motion commands. The installation speed of the flange under T1 must not exceed 250 mm/s, otherwise the safety stop 0 will be triggered. If the process requires higher speed, T2 should be used and personnel should be kept outside the danger zone.

Fault 6: RDC or mastering malfunction. Check X21 data cable, shielding, plug locking, RDC power supply, and EDS. After replacing the data cable, it is necessary to re master. If the axis data is lost, check the battery, RDC, and motor encoder wires. Mastering testing can use EMD or reference switches.

Fault 7: Over temperature or fan alarm. Check the spacing between the top, sides, and rear of the cabinet; Clean the heat exchanger, fan, and radiator; Check the KPP_SR/KSP_SR radiator, brake resistor, and temperature sensor inside the cabinet. Do not install filter cotton outside the ventilation port, otherwise it will increase the temperature and shorten the service life of the equipment.

Fault 8: The safety stop cannot be cancelled. Check external safety stop 1/2, safe operation stop US2、 Enable signal, operational safety, and safety interface feedback. Security stop cancellation usually does not require confirmation, but operational security recovery requires confirmation. If the safety controller detects an error, it may trigger the safety stop 0, and diagnostic information needs to be checked.

Fault 9: Abnormal load voltage of USS 2. Check if the Q5/Q6 contactors, fuses on CCU_SR, and US1/US2 are cross connected. If USS 2 cannot be turned off, it may cause unexpected actions of the actuator. It is necessary to confirm the contactor's suction and disconnection status according to the US2 functional inspection process.

Fault 10: Communication interruption. Check the connections of KCB, KSB, and KEB devices, WorkVisual configuration, bus terminal resistance, and shield grounding. If the device is not reconfigured after replacement, the system may not recognize the new device. When the secure communication is interrupted, the discrete secure interface will trigger the overall system E-STOP, while the Ethernet secure interface may generate a signal from the KUKA security controller to prevent the upper controller from triggering the overall E-STOP. However, the system integrator must consider this behavior in the risk assessment.

Maintenance and Support: Making Small Controllers Long Term Verifiable

Maintenance work must be carried out outside the danger zone; If entry is necessary, power must be cut off, tags must be hung, and electricity must be tested. After the controller is powered off, there may still be a residual voltage of up to 780 VDC in the intermediate circuit, and it is necessary to wait for at least 180 seconds. Follow ESD regulations during homework to prevent static electricity from damaging the board. Regularly inspect batteries, fans, contactors, fuses, labels, and warning signs. Nameplates, warning labels, and safety symbols shall not be removed or altered. Passwords should be changed before debugging and only authorized personnel should be informed.

When support is required, the robot model and serial number, controller model and serial number, energy supply system model and serial number, system software version, other software component versions, diagnostic package KRCDiag, application project, and external axis information should be prepared. The more complete the information, the faster the positioning.

The assembly and debugging of KR C4 smallsize-2 is essentially a systematic verification of the power chain, communication chain, and safety chain. Neglecting any of the following factors, such as installation spacing, grounding, battery, X11/X13/X66 safety interfaces, X20 motor interface, X21 RDC and US2, WorkVisual configuration, may result in shutdown, alarm, or more serious safety risks in automatic mode. For engineers, the most effective method is not to "power on first", but to confirm equipment compatibility, wiring correctness, safety function effectiveness, and data consistency layer by layer based on module replacement and fault tree logic. Only in this way can small controllers operate stably for a long time in compact workstations.