In recent years, the frequent occurrence of high-rise building fires has posed significant challenges due to their destructive power and救援 difficulties, leading to substantial casualties and property losses. Utilizing ropes to descend from platforms or windows is a relatively simple and feasible method, prompting the emergence of various high-rise escape devices. Since the 1980s, extensive research has been conducted on slow-descenders, broadly categorized into damping-type and deceleration disc-type devices. Damping-type descenders often exhibit increased descent speeds with heavier users, while deceleration disc-type devices tend to have complex structures, sometimes requiring motor drives or controls, making operation cumbersome and hindering widespread adoption. An ideal high-rise descent device should not only be safe and reliable but also possess the following characteristics: automatic speed control without manual adjustment to adapt to different weights, user-friendly operation requiring no specialized training or physical prowess, and a simple structure preferably without power units. To address these requirements, I have designed a novel high-rise descent device leveraging the deceleration effect of a cycloidal drive. This device segments the long descent distance from heights to the ground into multiple short intervals through a cyclic descent-deceleration motion, achieving graded slow descent. In this article, I will detail the design, analysis, and experimental validation of this device, emphasizing the pivotal role of the cycloidal drive mechanism.
The core innovation of my design lies in integrating a cycloidal drive with hydraulic damping to create a passive, self-regulating descent system. The device operates on the principle of converting the potential energy of the descending mass into controlled mechanical work and hydraulic dissipation, ensuring a safe and adaptive descent profile. The cycloidal drive, known for its high reduction ratio and compactness, serves as the primary speed reduction element, while the hydraulic damping provides the necessary resistive force to decelerate the user intermittently. This combination allows for automatic adaptation to varying weights without user intervention, meeting the key requirements for emergency escape equipment. Throughout the development process, I focused on optimizing the cycloidal gear geometry, ensuring structural integrity through finite element analysis, and validating performance via prototype testing.
The overall structure of the descent device comprises four main components: a manual rewinding mechanism, a winding drum, a deceleration mechanism (centered on the cycloidal drive), and a damping mechanism. The manual rewinding mechanism includes a pair of gears with a 3:1 transmission ratio for quick rope retrieval. Two one-way clutches are incorporated to enhance operability: one between the manual rewinding mechanism and the winding drum prevents the handle from spinning during descent, avoiding injury, and another between the winding drum and the cycloidal drive reduces rewinding resistance. The winding drum has a variable diameter, with an inner circle of 63 mm and an outer circle of 102 mm, accommodating rope storage for multi-story descents. The deceleration mechanism is a cycloidal drive reducer, where the cycloidal gear’s output is coupled to a cam profile. The damping mechanism is a hydraulic cylinder with a piston featuring a one-way check valve and a damping orifice. When the piston is pushed down by the cam during the deceleration phase, fluid flows from the lower chamber to the upper chamber through the damping orifice, creating resistance; during the return stroke, fluid bypasses through the check valve with minimal resistance.
The operational sequence is as follows: as the user descends, the rope unwinds from the drum, rotating it. Through the cycloidal drive, the drum’s multiple rotations are reduced to a single rotation of the output cam. During the cam’s return stroke, the piston is disengaged, allowing free descent. During the cam’s push stroke, the piston is depressed, activating the hydraulic damping to decelerate the descent until it momentarily stops. This cycle repeats every approximately 0.8 to 1 meter of descent, effectively creating a step-wise descent pattern. This design mimics the controlled descent of trained professionals, such as firefighters, but in an automated, mechanical form. The use of a cycloidal drive is crucial here due to its ability to provide a high reduction ratio in a compact space, ensuring the device remains portable and easy to deploy.
The cycloidal drive, often referred to as a cycloidal speed reducer or cycloidal gearbox, operates on the principle of harmonic传动. It consists of an eccentric input shaft, a cycloidal disk (or摆线轮), and a ring of stationary pins (the针轮). As the eccentric shaft rotates, it causes the cycloidal disk to undergo a compound motion—both rotation and revolution—relative to the pins. This motion results in a significant speed reduction between the input and output. In my design, the cycloidal drive is customized to achieve a specific reduction ratio suitable for the descent intervals. The selection and design of this cycloidal drive were central to ensuring the device’s performance and reliability.
To achieve the target descent interval of about 1 meter per cycle, I calculated the required reduction ratio based on the average circumference of the winding drum. With an inner diameter of 63 mm and outer diameter of 102 mm, the average circumference is approximately 263 mm. Thus, the reduction ratio needed is: $$ i = \frac{1000 \text{ mm}}{263 \text{ mm}} \approx 3.93 $$ I rounded this to a ratio of 4 for design simplicity. The cycloidal drive was designed with a pin gear (stationary ring) having 12 teeth (pins) and a cycloidal disk having 9 teeth, which inherently provides a reduction ratio equal to the difference in tooth counts or related to the number of lobes. For a cycloidal drive, the reduction ratio \( i \) can be expressed as: $$ i = \frac{Z_p}{Z_p – Z_c} $$ where \( Z_p \) is the number of pins and \( Z_c \) is the number of lobes on the cycloidal disk. With \( Z_p = 12 \) and \( Z_c = 9 \), the ratio is: $$ i = \frac{12}{12 – 9} = 4 $$ This perfectly matches the requirement.
The tooth profile of the cycloidal disk is critical for smooth operation and load distribution. I derived the parametric equations for the cycloidal curve based on standard formulations but adapted for manufacturing constraints. In a Cartesian coordinate system, the profile of the pin gear (circle centers) and the cycloidal disk can be described. For the pin gear, the coordinates of the pin centers are given by: $$ X_p(t) = R \sin\left(\frac{t}{2Z_p}\right) – 2r \sin\left(\frac{t}{2}\right) \cos\left(\frac{t}{2} + \frac{t}{2Z_p}\right) $$ $$ Y_p(t) = R \cos\left(\frac{t}{2Z_p}\right) + 2r \sin\left(\frac{t}{2}\right) \sin\left(\frac{t}{2} + \frac{t}{2Z_p}\right) $$ For the cycloidal disk, the lobe profile is: $$ X_c(t) = R \sin\left(\frac{t}{2Z_c}\right) – 2r \sin\left(\frac{t}{2}\right) \cos\left(\frac{t}{2} – \frac{t}{2Z_c}\right) $$ $$ Y_c(t) = R \cos\left(\frac{t}{2Z_c}\right) – 2r \sin\left(\frac{t}{2}\right) \sin\left(\frac{t}{2} + \frac{t}{2Z_c}\right) $$ where \( R \) is the base circle diameter of the cycloidal disk, \( r \) is the pin circle radius, and \( t \) is the parameter ranging from 0 to \( 2\pi \). Here, \( R = 2r Z_c \) to ensure proper engagement. I set \( r = 15 \text{ mm} \), so \( R = 2 \times 15 \times 9 = 270 \text{ mm} \). These equations were used to generate the tooth profiles in CAD software, ensuring accurate geometry for the cycloidal drive components.
Strength analysis of the cycloidal drive is essential due to the high loads during descent. The primary failure modes are surface pitting and bending fatigue at the tooth root. The contact stress between the cycloidal disk and pins can be evaluated using the Hertzian contact stress formula: $$ \sigma_j = 0.0418 \sqrt[3]{\frac{P_i E_d}{B \rho_d}} \quad \text{(MPa)} $$ where \( P_i \) is the normal force at the contact point, \( E_d \) is the equivalent modulus of elasticity (for alloy steel, \( E_d = 200 \text{ GPa} \)), \( B \) is the width of the cycloidal disk, and \( \rho_d \) is the equivalent curvature radius at the contact point. For bending strength, I adapted the standard gear bending formula: $$ \sigma_f = \frac{K F_t Y_{Fa} Y_{Sa}}{B m} \leq [\sigma_f] $$ where \( [\sigma_f] \) is the allowable bending stress, \( m \) is the module (effectively larger for cycloidal gears, determined empirically), \( K \) is the load factor (taken as 1.98), \( F_t \) is the tangential force, \( Y_{Fa} \) is the form factor (approximately 2.44 for cycloidal profiles), and \( Y_{Sa} \) is the stress correction factor (approximately 1.65). These calculations ensured that the cycloidal drive could withstand the maximum expected load of 200 kg without failure.
To validate the structural integrity, I conducted finite element analysis (FEA) on the entire device. The geometric model was created in SolidWorks and then imported into HyperMesh for meshing. The mesh consisted of tetrahedral Solid187 elements, with refined grids at critical areas like the cycloidal drive and piston rod. The total element count was 863,242. Material properties were assigned: for the base plate, side plates, winding drum, and cycloidal components, elastic modulus \( E = 206 \text{ GPa} \), Poisson’s ratio \( \mu = 0.3 \), density \( \rho = 7.8 \times 10^3 \text{ kg/m}^3 \); for the hydraulic cylinder, \( E = 69 \text{ GPa} \), \( \mu = 0.33 \), \( \rho = 2.9 \times 10^3 \text{ kg/m}^3 \). The analysis was performed in ANSYS under a static structural load equivalent to a 200 kg mass.
The FEA results revealed stress distributions关键 areas. For the pin gear, the maximum equivalent stress occurred at the contact points with the cycloidal disk, as shown in the contour plots. Similarly, the cycloidal disk exhibited higher stress concentrations at the lobe roots. Both values were well below the yield strength of the alloy steel, confirming sufficient fatigue resistance. The support plates showed maximum stress at the base attachment points due to bending moments, but within safe limits. These insights guided design refinements, such as adding fillets or increasing thickness in high-stress zones, to enhance durability. The table below summarizes the maximum equivalent stresses from FEA for key components:
| Component | Maximum Equivalent Stress (MPa) | Material Yield Strength (MPa) | Safety Factor |
|---|---|---|---|
| Pin Gear | 20.04 | >600 | >30 |
| Cycloidal Disk | 107.47 | >600 | >5.6 |
| Support Plate | 3.28 | >250 | >76 |
The low stresses indicate a robust design, particularly for the cycloidal drive elements, which are central to the device’s function. This analysis gave me confidence in the device’s ability to handle repeated use without structural failure.
Prototype testing was conducted to evaluate real-world performance. The descent device was installed at a height of 6.5 meters (simulating a third floor), and tests were performed with different loads: 15 kg, 40 kg, and 64 kg (a human subject). The descent time and average speed were recorded for each case. The results are presented in the following table:
| Load (kg) | Total Descent Height (m) | Descent Interval per Cycle (m) | Total Time (s) | Average Speed (m/s) |
|---|---|---|---|---|
| 15 | 6.5 | 0.8 | 7.8 | 0.83 |
| 40 | 6.5 | 0.8 | 6.4 | 1.02 |
| 64 | 6.5 | 0.8 | 5.3 | 1.22 |
The data confirms that the device successfully achieves cyclic descent with consistent intervals regardless of load, demonstrating the self-adapting特性 of the design. As load increases, the average descent speed rises slightly due to increased force on the hydraulic piston, leading to faster fluid flow through the damping orifice. However, the variation is minimal, and all speeds remain within a safe range (typically below 1.5 m/s for emergency descents). The cycloidal drive performed flawlessly, providing the precise reduction needed to trigger the deceleration cycle at each interval. This test validates the practical feasibility and safety of the device for various user weights.
In discussing the results, it is important to highlight the advantages of using a cycloidal drive in this application. Compared to traditional gear reducers, cycloidal drives offer higher reduction ratios in a more compact package, which is crucial for portable escape devices. They also have multiple tooth contacts, distributing load evenly and reducing wear, thereby enhancing longevity. Furthermore, the inherent rigidity of cycloidal drives minimizes backlash, ensuring precise control over the descent intervals. My design leverages these benefits to create a reliable, maintenance-free system. The integration with hydraulic damping allows for smooth energy dissipation, avoiding jerky motions that could destabilize the user.
However, there are limitations to consider. The current design relies on a fixed damping orifice, which limits the adaptability to extreme weight ranges. Future iterations could incorporate adjustable orifices or smart valves to optimize performance across a broader spectrum. Additionally, the cycloidal drive, while robust, requires precise manufacturing to avoid noise and vibration. Advances in 3D printing or precision casting could mitigate this cost. Despite these, the device represents a significant step forward in passive escape technology, offering a balance of simplicity, safety, and effectiveness.
In conclusion, I have developed a novel high-rise descent device that utilizes a cycloidal drive for speed reduction and hydraulic damping for controlled deceleration. The design achieves automatic adaptation to different user weights without manual intervention, operating through a cyclic descent-deceleration pattern that ensures safety and speed. Through detailed design, finite element analysis, and prototype testing, I have demonstrated the device’s structural integrity and functional performance. The cycloidal drive is central to this innovation, providing the necessary reduction in a compact and reliable manner. This research contributes to the field of emergency escape equipment by offering a mechanical, non-powered solution that is easy to use and manufacture. Future work will focus on optimizing the damping mechanism and exploring materials to reduce weight further, potentially integrating smart sensors for enhanced safety monitoring.
The successful implementation of this cycloidal drive-based device underscores the potential of mechanical ingenuity in solving real-world safety challenges. As urban densities increase, such innovations become ever more critical, and I believe that continued refinement of this technology could lead to widespread adoption in buildings worldwide, saving lives in emergency situations.