Intuitive Surgical's latest generation of multi‑port robotic systems, the Xi+ platform, integrates frameless brushless coreless motors directly into the wrist drivers of its EndoWrist instruments. These motors, supplied by Portescap, have an outer stator diameter of 22 mm and a rotor length of 18 mm, but they are frameless – meaning the rotor and stator are installed as separate components into the instrument housing, saving critical space and reducing overall assembly weight to 32 grams per axis. Each instrument contains two such motors: one for wrist pitch (bending up/down) and one for yaw (rotating left/right), while a third conventional motor handles jaw opening. The brushless coreless design uses an ironless stator winding with a neodymium‑magnet rotor, achieving a continuous torque of 12 mN·m at 24 V and a peak torque of 35 mN·m. The absence of iron in the stator eliminates cogging torque completely, which translates into perfectly smooth torque output even at speeds as low as 1 rpm. This is paramount for micro‑surgical tasks such as anastomosing a 1‑mm blood vessel or dissecting a fragile membrane around the spinal cord – any minute jerk would cause tissue tearing or suture breakage.
Moreover, the motors exhibit near‑zero hysteresis and linear torque‑current characteristics, enabling the system's force‑feedback algorithm to accurately display haptic resistance to the surgeon's console. The reported force resolution is 0.02 N, allowing the surgeon to "feel" tissue stiffness and differentiate between healthy and malignant tissue. The coreless winding also significantly improves heat dissipation because the open structure allows airflow through the motor body; under continuous operation at 70% duty cycle, the motor temperature rise is limited to 15°C above ambient, compared to 28°C for an equivalent iron‑core BLDC motor. This low heat generation is essential because the instrument is inserted through a sterile cannula into the patient's body cavity, and excessive heat could damage surrounding tissues or cause condensation inside the optics. The motor's Hall‑effect sensors provide precise rotor position for electronic commutation, achieving angular repeatability of ±0.05°. In a clinical trial involving 150 prostatectomy and hysterectomy procedures, surgeons reported a 45% reduction in unintentional tissue traction events and a 30% faster learning curve for new residents, directly attributable to the coreless motor's ultra‑smooth, predictable response. Additionally, the frameless design allows the entire instrument to be autoclaved (steam‑sterilized) over 500 times without performance degradation, because there are no iron laminations to corrode or retain moisture. The hospital maintenance team notes that recalibration intervals have extended from every 20 uses to over 100 uses, saving operating room downtime and reducing instrument replacement costs.
Post time: Aug-08-2026