A Dual-Motor Actuator for Ceiling Robots with High Force and High Speed Capabilities

TL;DR

This work addresses the need for ceiling-based patient lifts that combine high-force transfer with high-speed assistance and reliable fall protection. It introduces a dual-motor actuator with a planetary differential and a brake-enabled transition strategy, underpinned by a lumped-parameter model with the key relations $v_0/r = \omega_1/R_1 + \omega_2/R_2$ and $F_m r = R_1 \tau_1 = R_2 (\tau_2 - \tau_B \;\mathrm{sign}(\omega_2))$, plus a friction model $\tau_f = ( b |\omega_2| + c + d F_d ) \tanh(\omega_2)$ to support force control. The authors compare architectures, develop control algorithms for transfer, assistance, and fall prevention, and validate a full prototype that lifts up to 318 kg at 0.05 m/s, unloads 59 kg at 0.55 m/s, and achieves force-tracking errors of 7.8% (low speed) and 12% (high speed). A fall-prevention sequence demonstrates controlled braking via a disk brake and coordinated motor action to minimize fall distance, with clinical evaluation highlighted as future work. Overall, the approach enables a compact, efficient, multifunction ceiling lift capable of supporting rehabilitation and mobility tasks in healthcare settings.

Abstract

Patient transfer devices allow to move patients passively in hospitals and care centers. Instead of hoisting the patient, it would be beneficial in some cases to assist their movement, enabling them to move by themselves. However, patient assistance requires devices capable of precisely controlling output forces at significantly higher speeds than those used for patient transfers alone, and a single motor solution would be over-sized and show poor efficiency to do both functions. This paper presents a dual-motor actuator and control schemes adapted for a patient mobility equipment that can be used to transfer patients, assist patient in their movement, and help prevent falls. The prototype is shown to be able to lift patients weighing up to 318 kg, to assist a patient with a desired force of up to 100 kg with a precision of 7.8%. Also, a smart control scheme to manage falls is shown to be able to stop a patient who is falling by applying a desired deceleration.

Figures (11)

• Figure 1: Lifting module overview of the prototype in a real situation with illustrations of its three operating conditions, A) Patient Transfer, B) Patient Assistance, C) Fall prevention. HF is for highly-geared mode (high-force) and HS is for lightly-geared mode (high-speed).
• Figure 2: Operation points mapping (continuous force) with high-force for patient transfer, high-speed for patient assistance and brake for fall prevention.
• Figure 3: Generic concepts for design comparison, more specifically the ratios of each gear stages based on the requirements and the selected components.
• Figure 4: Multifunctional lift experimental prototype and scheme of the actual gearing topology.
• Figure 5: Simplified model of the multifunctional lift using a lumped-parameter approach.