What the Controller Doesn't Know: Designing Electronics for Surgical Robotics

Closing the latch on a tool isn't the end of a tool change. The controller needs to know that the tool-change mechanism closes correctly, register the new instrument, load its parameters, and decide if and when the next movement can safely occur. Similar situations occur elsewhere in the robot: a joint encoder is reporting its nominal position, even as the robot arm vibrates; a sensor that showed no noise on the test bench starts picking up interference next to a motor driver; and a power stage tucked into a miniature joint runs far hotter than expected. 

All of these are cases of the controller not receiving the information that it needs from the electronics to understand and control the system. The task is to understand what the robot and its various peripherals have to say to the controller, what different circuits say about the robot's condition, state, or planned activity, and what additional sensors or protection circuits could be useful in diagnosing a situation or preventing damage.

Position Is Only Part of Motion

A joint encoder may be able to report rotational position on a revolute joint, but it may not reveal link compliance or vibration elsewhere on the arm. A 6-axis inertial sensor mounted on the robot arm provides another perspective on motion.

The Murata SCH16T-K01 inertial sensor, for instance, includes a 3-axis gyroscope with bias instability down to 0.3°/h and noise density down to 0.4m°/s/√Hz, plus a 3-axis accelerometer.

Two brief remarks are in order on this sensor. First, time synchronization allows the inertial measurements to be aligned with data such as the joint-encoder output. When combining the data, the system still must account for sampling, latency, and bandwidth. Cross-axis compensation and stable performance across temperature can reduce the need for calibration, but that benefit still depends on integration in the finished system. Second, it should be remembered that it does not directly provide the position of the end effector. The inertial sensor can supply answers to other questions that are relevant to determining or understanding motion, though.

Feedback quality can also be a function of the motor-drive electronics. Multi-axis motor drives tend to be miniaturized, and decoupling capacitors can be exposed to board flex and vibration, while high-permittivity dielectrics can show a reduction in effective capacitance under DC bias that is not apparent from the nominal capacitance value.

Murata's ceramic-capacitor range, for instance, includes case sizes as small as the 008004 inch size (0.25×0.125mm), as well as soft- and metal-termination options intended to improve resistance to cracking under board flex and mechanical or thermal stress.

What the surgical system is looking to detect at the business end of the instrument is a press, release, flex, or vibration; the Picoleaf piezoelectric film sensor from Murata is 0.2mm thick or less and can fit in spaces where a rigid sensor package would be impractical, taking advantage of a different set of physics than a typical strain gauge.

Picoleaf's output depends on the speed and direction of its deformation and requires careful consideration of mounting, circuitry, and mechanical connections to the business end in order to get useful information about the sensed event. The behavior of the sensor under temperature gradients is another easy pitfall, and one that is particularly relevant in an operating room.

The tip of an instrument close to a surgical site can experience widely varying temperatures due to the patient's body heat, warmed irrigation fluid, and the resistive tissue heating produced by an electrosurgical unit. Temperature changes can generate an unwanted output in a pyroelectric film; Picoleaf is non-pyroelectric, which reduces that source of signal, although the finished sensing assembly still requires temperature validation.

The MRMS166R AMR sensor from Murata is a contactless magnetic switch in a 1.0 x 1.0 x 0.45mm package with typical current consumption of 20nA at 1.5V, low enough to suit a battery-powered instrument. However, for faster switching applications, Murata's MRMS543E is better suited.

Keeping the Measurement Intact

While the choice of a sensor is important, it is just one factor that must be considered in the design. Electrical noise on a robot arm can couple into nearby encoder and sensor wiring and cause a measurement error or lead the controller to report an incorrect state, such as an open latch or detached tool.

Either can be serious, but an incorrect state can lead the controller to act on something that has not happened. The engineer should understand how the noise is coupling into the signal path and take that into account when applying filters or other noise-suppression features. A false state indication can be more serious than a noisy measurement, which is why the coupling paths should be identified before suppression components are selected. 

Filtering can help, but layout, routing, and the coupling path also matter. For surgical robotics, Murata’s EMI/inductor selection is a curated list that promotes the highest-reliability products from powertrain/safety grade components. For more information on this candidate list and policies, please reach out to your local Sales Rep. or Murata Sales contact.

BLM-family chip ferrite beads provide frequency-dependent impedance on selected power or signal lines to suppress conducted noise. Murata offers a broad range for different applications, as well as different sizes and current ratings. The component should be chosen considering the noise spectrum, current, signal bandwidth, and permissible waveform distortion level. For instance, for common-mode noise on a differential pair, an appropriately selected common-mode choke can suppress common-mode current while minimally affecting the desired signal.

Murata provides signal-line common-mode chokes for interfaces with data rates up to 12Gbps and separate power-line versions rated up to 18A, but an appropriate part has to be chosen for a particular application based on the interface specification, current requirements, noise spectrum, package, and operating temperature.

What makes this approach actually practical is SimSurfing, Murata's online component-selection and simulation tool. Engineers can compare the frequency characteristics of candidate components, assess those data against measured noise spectra and signal bandwidths, and then verify the choice when prototyping.

It's a vastly different process than having to desolder things and put on a generic filter after an EMC test has failed, and one that doesn't have to come with awkward questions from management if the wrong part is chosen.

Isolation in the Space You Have

There are at least two power supply challenges related to the surgical robot. The first is a supply for a local measurement or control circuit, which may require an isolated rail. The second is the mains AC supply for the equipment.

For the local isolated rail, isolation voltage is only one parameter. Galvanic isolation removes the direct electrical connection, but fast common-mode current can still couple through parasitic capacitance across the barrier into sensitive secondary-side circuitry. The NXJ1T isolated DC-DC converter from Murata provides 4.2kVDC HiPot test isolation in a 10.55 × 13.70 × 4.04 mm SMD package. Its low isolation capacitance helps limit that common-mode current.

The NXJ1T employs the company’s proprietary block-coil transformer technology. Murata points out that some alternative solutions using wireless-power-coil architectures have lower coupling factors, operate at switching frequencies of the order of 10 MHz, and realize only 40–60% efficiency. The NXJ1T operates at a lower switching frequency of 500kHz to 2MHz and offers approximately 80% efficiency. It also provides common-mode transient immunity, enabling it to tolerate fast common-mode transients in a high-noise environment, such as a PCB with a switched-mode motor driver. However, the overall system’s noise immunity still has to be analyzed and verified during development.

Meanwhile, the PQC600 AC-DC power supply addresses the second challenge, the mains supply for the equipment. It delivers 600W with forced-air cooling (350W convection cooling), has a height of less than 1U, achieves 95% efficiency at full load, and is certified to IEC 60601 Ed.3 medical (2 x MOPP Pri-Sec; 1 x MOPP Primary-Chassis Ground, 1 x MOPP output to chassis). It also includes Applied Part Type B & BF rated (isolation and patient leakage current performance). For lower power applications, there is also the PQC250, which provides 250W o/p power.

The key difference between the two power supplies is that the locally mounted NXJ1T isolated DC-DC converter is employed to provide isolated rails for local signal conditioning circuits, while the PQC600 AC-DC power supply serves as a certified building block at the mains input.

From the output of the isolated converter, pSemi-Murata provides several high-efficiency, low-profile charge-pump capacitor dividers to convert to stable, lower voltage levels - ideal for space-constrained applications, such as surgical robots. The PE25304 and PE25204 step-down from 48V rails by dividing by 4 to provide a stable 12V@6A equipment supply, while the PE25208 divides by 2 or 3 from a 48V or 24V input with an output current of up to 10A. For 12V input voltage applications, the PE25213 divides by 2 or by 3 to create a 6V or 4V rail, respectively, with a maximum of 10A. These can serve as the input to the point-of-load regulators provided by Murata’s Mono and Pico product families. 

For applications requiring high-current point-of-load conversion in a compact footprint, Murata’s MonoBK series of non-isolated DC-DC converters provides an efficient solution. The modules integrate key power-conversion functions into a small package, reducing external component count and simplifying PCB layout. This approach is particularly useful in surgical robotics, where high-performance processors, FPGA devices, imaging electronics, and motion-control circuits often require multiple low-voltage, high-current rails located close to the load. By placing efficient point-of-load regulation near these devices, designers can reduce distribution losses, improve transient response, and help manage thermal constraints inside compact electronic assemblies.

Heat Has Nowhere To Go

A small joint can create little space for the motor and power electronics. To install the sensor in an easily accessible place, it is not always possible to place it directly at the hottest spot. The controller may respond too late, or, conversely, the temperature of the entire casing may be used instead of the desired value.

This can be solved by choosing the right sensor. Thanks to their miniaturized design, NTC thermistors from Murata in the NCU series can be used in tight mechanical structures. The smallest package in the series is 0.6 × 0.3mm. Some NCU03 parts have a 1% resistance tolerance and are rated for operation up to 125°C. Some 1.0 × 0.5 and 1.6 × 0.8mm variants, in turn, are rated for operation up to 150°C. Of course, the choice of thermistors also depends on the desired resistance, tolerance, and temperature. The complete range of options is indicated in the product specification.

Thus, in a suitable measurement circuit, a properly selected thermistor mounted close to a winding or power stage can provide the controller with a more representative local temperature signal for its task: compensation, derating, warning, or shutdown. It is important to remember that the location of the sensor must be verified in the assembled circuit since placement in an inappropriate place will provide misleading results.

A Change of Tool Also Involves Data

Closing the latch is insufficient information for the robot to know which tool has been installed. By using appropriate magnets and mechanisms, an AMR switch could be used to sense either the latch or the attachment state. Then, a UHF reader could be used to read the tag's ID and contents. Host software could use the tool's identity to retrieve operating instructions, usage and reprocessing logs, or service records before proceeding, if needed.

That is different from requiring a visual inspection, sterilization record, or clinical authorization. An optical code could be used to identify the instrument, but the reader must be able to see it. A different orientation or number of uses may hide useful markings; RFID removes the line-of-sight and marking-wear limitations, although orientation can still affect read performance. However, RFID implies a different set of requirements to be addressed: those of location, presentation, materials, and RF interactions.

Item Identification 

Accurately identifying items in robotic automation systems has become increasingly important. Implementing a successful RFID (Radio Frequency Identification) system is an accurate and efficient method for keeping track of these items. When an RFID tag is applied to an individual item, the tag often remains a permanent fixture on that device. Not only does this allow this item to be correctly identified, but when integrated with the host system, additional information can be quickly realized, such as total time usage, processing logs, operating instructions, and item calibration.

Murata’s UHF Micro tag series is available in two sizes (as small as 1.2 × 1.2 × 0.55mm), where the smallest HF/NFC tag measures only 3.2 x 3.2 x 0.7mm. All micro tags are designed with an integrated antenna that is compatible with an over-molding process. Read range performance is typically 20 ~ 30mm, which is ideal for individual product identification.

Mounting RFID tags on metal poses a bigger challenge than on other materials because nearby metal can limit the performance of a conventional RFID tag. Murata’s LXTBKZMCMG-010 on-metal tag is designed to be applied to a metal object and utilizes the metal surface as a booster antenna. The tag measures 6.0 × 2.0 × 2.3mm, and Murata specifies a reference read range of up to 1.5m on metal at 4W EIRP. Performance will depend on the placement of the tag and RF environment. It’s always recommended that the user validate the device under the conditions it will be used in; this includes reprocessing, sterilization, temperature, and so on.

The 2EG offers onboard and supported external antenna options, while the module-level radio approvals, test documentation, and design support from Murata help shorten the RF design-in cycle. The 48MHz Arm Cortex-M33 MCU core can run application code, whereas CryptoCell 312 can support cryptographic functions. Nevertheless, these capabilities are not sufficient to ensure security and reliability on their own. The application software, its updates, security, and antenna and radio configuration, as well as wireless coexistence, end-product radio and EMC approvals, and any applicable hospital-network integration, are the responsibility of the host equipment manufacturer.

Where the Evidence Has To Come From

At this point, component data has done its job: it has winnowed the options down. However, it is not a safety case. IEC 80601-2-77, the standard for basic safety and essential performance of robotically assisted surgical equipment and systems, includes specific requirements for electromagnetic emissions and immunity. IEC 60601-1-2 covers electromagnetic compatibility (EMC) at the equipment and system level.

For EMC, the power supply, sensor lines, motor-drive electronics, and wireless links can’t be evaluated in isolation. They have to be evaluated and tested in the final equipment or system configuration against the applicable EMC requirements for the intended-use environment.

The wider validation plan must cover relevant system and subsystem configurations, including the temperature gradients, cable configurations, loads, fault conditions, and wireless-coexistence environments the equipment is likely to encounter. Similarly, medical instruments and assemblies subjected to cleaning and sterilization have to be validated for the intended reprocessing methods and number of cycles.

Murata’s contribution to the safety case is more limited, but no less important. The block-coil construction of its isolated DC-DC converter offers specified isolation in a compact package with low capacitance across the isolation barrier. Its RFID portfolio includes microtags for embedding in molded parts, and a tag that can be mounted directly on metal. With SimSurfing, engineers can access characterized data on components to help identify candidates for noise suppression before measuring noise spectra on a prototype that incorporates them. Murata can also help evaluate RFID mounting options and RF performance.

These are contributions worthy of consideration, but they are still contributions. The ultimate responsibility for obtaining the evidence needed to demonstrate compliance belongs to the manufacturer of the completed surgical robot. The manufacturer must also confirm with Murata that each selected part is suitable for the intended medical use.

Reference

Murata Manufacturing Co., Ltd. (2026). Application Guide: Surgical Robotics. February 2026.