📚 Case Study in Action: Design and Analysis of an Adjustable Desk Lamp | 案例分析实战演练：可调节台灯的设计与分析
In this case study, we will walk through the complete engineering design process for an adjustable desk lamp. You will see how a real-world product is taken from an initial need, through research, specification, idea generation, material selection, mechanical analysis, manufacturing, and final evaluation. This mirrors the kind of problem-solving and analytical thinking required for CAIE IGCSE Engineering, helping you understand how theory is applied in practice.
在本案例研究中，我们将完整地走过可调节台灯的工程设计全过程。你将看到一件真实产品如何从初始需求出发，经历调研、规格制定、创意构思、材料选择、力学分析、制造到最终评估。这模拟了 CAIE IGCSE 工程所要求的解决问题与分析思维，帮助你理解理论如何在实际中应用。
1. Introduction to the Case Study | 案例介绍
Adjustable desk lamps are found in millions of homes and offices. Their primary function is to provide focused, directional light that can be repositioned to suit the user’s task. This case study focuses on a classic articulated-arm lamp with a base clamp, parallel arms, spring-loaded hinges, and a rotatable shade.
可调节台灯存在于无数家庭和办公室中。其主要功能是提供可重新定位的定向照明，以适应使用者的任务需求。本案例研究的对象是一款经典铰接臂台灯，它带有底座夹具、平行臂、弹簧铰链和可旋转灯罩。
Engineers must balance ergonomics, aesthetics, cost, ease of manufacture, and electrical safety. By examining each stage of development, you will learn to evaluate design decisions and justify choices using engineering principles.
工程师必须平衡人体工学、美学、成本、制造便利性与电气安全。通过审视开发过程的每个阶段，你将学会用工程原理评估设计决策并论证选择。
2. Identifying the Need and Design Brief | 确定需求与设计简报
The initial need was identified through user feedback: many students and professionals complained of fixed desk lamps that caused glare or required them to adopt awkward postures. The design brief was stated as: 'Design a portable, adjustable desk lamp that clamps securely to a desk edge, allows easy repositioning with one hand, and provides glare-free lighting for study and precision work.'
初始需求是通过用户反馈确定的：许多学生和专业人士抱怨固定式台灯会造成眩光或迫使他们采取别扭的姿势。设计简报表述为：“设计一款便携式可调节台灯，能牢固地夹在桌边，允许单手轻松重新定位，并为学习和精细工作提供无眩光照明。”
Key constraints were identified: the lamp must be stable when fully extended, its clamp must fit desk thicknesses between 15 mm and 40 mm, the maximum reach should be at least 600 mm, and the light source must be an energy-efficient LED with a colour temperature of around 4000 K.
关键约束条件被确定：台灯在完全伸展时必须稳定，其夹具必须适配 15 毫米至 40 毫米的桌面厚度，最大伸展距离至少为 600 毫米，且光源必须为色温约 4000 K 的高效 LED。
3. Product Research and Design Specification | 产品调研与设计规格
Existing products were analysed, including the classic Anglepoise® lamp and low-cost copycat models. Common failures were identified: weak springs that sagged over time, plastic hinges that cracked, and poor wiring that led to short circuits. A detailed design specification was drawn up.
现有产品被分析，包括经典的 Anglepoise® 台灯和廉价的仿制型号。常见的失效模式被找出：随时间松弛的弱弹簧、开裂的塑料铰链，以及导致短路的劣质布线。一份详细的设计规格书被制订出来。
| Performance requirement 性能要求 | Value / Detail 数值/细节 |
|---|---|
| Maximum reach 最大伸展距离 | 650 mm from clamp pivot |
| Spring holding force 弹簧保持力 | Must support 1.2 kg head at any angle without drift |
| Clamp clamping force 夹具夹紧力 | ≥ 200 N without damaging surface |
| LED luminous flux LED 光通量 | 500 lm at 30 cm, CRI > 80 |
| Electrical safety 电气安全 | Double insulated, fuse in plug (3 A), IP20 rating |
The specification served as a fixed reference point against which all design ideas were judged. Any proposed solution that failed to meet these criteria was discarded early.
这套规格书作为一个固定的参考基准，用来评判所有设计方案。任何不能达到这些准则的提案都在早期被淘汰。
4. Generating Creative Design Ideas | 构思创意设计方案
Three distinct concepts were sketched and modelled roughly. Concept A used a single curved flexible metal gooseneck. Concept B used a four-bar linkage with coil springs. Concept C used a balanced parallel-arm mechanism with tension springs, closely resembling the traditional Anglepoise® layout.
三个不同的概念被草绘并粗略建模。方案 A 采用单根弯曲的金属软管。方案 B 使用四杆连杆机构加螺旋弹簧。方案 C 采用带拉伸弹簧的平衡平行臂机构，与传统的 Anglepoise® 布局相似。
Concept A was rejected because the gooseneck could not hold the LED head steadily when extended and suffered from metal fatigue. Concept B was complex, with many pin joints that would wear quickly. Concept C offered the best combination of stability, smooth adjustment, and proven reliability. It was selected for development.
方案 A 被否决，因为金属软管在伸展时不能稳定地支撑 LED 灯头，且存在金属疲劳。方案 B 结构复杂，许多销接点会迅速磨损。方案 C 提供了稳定性、顺畅调节和可靠性的最佳组合，被选中进行深入开发。
5. Developing the Chosen Solution | 深化选定方案
The parallel-arm mechanism relies on a system of tension springs that counteract the gravitational moment of the lamp head. The upper and lower arms are equal in length, forming a parallelogram linkage. This geometry keeps the lamp head orientated in the same plane as the arm is raised or lowered, maintaining a constant beam angle.
平行臂机构依靠一套拉伸弹簧系统来抵消灯头的重力矩。上下臂等长，构成平行四边形连杆机构。这种几何布局使得在抬升或下降上臂时灯头保持在同一平面取向，使光束角恒定。
Detailed CAD (Computer-Aided Design) models were produced using parametric software. The pivot joints were designed with nylon bushings to reduce friction and noise. The lamp shade was given a ventilated shape to dissipate LED heat. The clamp body was shaped using FEA (Finite Element Analysis) to minimise stress concentrations.
使用参数化软件创建了详细的 CAD 模型。枢轴接点采用尼龙衬套以减小摩擦和噪音。灯罩被设计成通风形状以发散 LED 热量。夹具主体借助有限元分析 (FEA) 来最小化应力集中。
6. Material Selection and Justification | 材料选择与论证
Material choice directly affects cost, strength, weight, and manufacturing. A selection matrix was used, scoring each candidate material against criteria such as tensile strength, density, corrosion resistance, and price.
材料选择直接影响成本、强度、重量和制造。使用了选择矩阵，根据抗拉强度、密度、耐腐蚀性和价格等标准为每种候选材料打分。
| Component 部件 | Material chosen 所选材料 | Justification 理由 |
|---|---|---|
| Arms 臂杆 | Mild steel tube with chrome plating | High stiffness-to-weight ratio, corrosion protection, low cost |
| Spring hooks 弹簧挂钩 | Stainless steel (304 grade) | High fatigue resistance, no plating needed |
| Pivot bushings 枢轴衬套 | Nylon 6,6 | Self-lubricating, quiet, durable |
| Clamp screw handle 夹具手柄 | ABS plastic, injection-moulded | Good grip, cheap to mass-produce |
| Lamp shade 灯罩 | Aluminium alloy, spun-formed | Excellent thermal conductivity, lightweight |
In every case, the selected material meets the functional requirements while keeping the total bill of materials within the target cost of £8.50 per unit.
每一种情况下，所选材料都满足功能要求，同时将物料清单总成本控制在每台 8.50 英镑的目标之内。
7. Mechanical Analysis – Forces and Moments | 力学分析——力与力矩
When the arm is fully extended horizontally, the lamp head exerts a maximum moment about the shoulder pivot. The spring tension must be designed to balance this moment to allow the user to position the lamp with minimal effort.
当臂杆完全水平伸展时，灯头对肩部枢轴施加最大力矩。弹簧张力必须设计得能平衡这一力矩，以便使用者用极小力气就能定位台灯。
avitational force is W = m₁ × g = 0.8 × 9.81 ≈ 7.85 N. The moment due to the lamp head is:
假设灯头质量 m₁ = 0.8 kg，其重心到枢轴的距离 L₁ = 0.45 m。重力为 W = m₁ × g = 0.8 × 9.81 ≈ 7.85 N。灯头产生的力矩为：
Mhead = W × L₁ = 7.85 N × 0.45 m = 3.53 N·m
stance of d = 0.08 m from the pivot. To keep the system in equilibrium, the spring force Fspring required is:
拉伸弹簧的固定点到枢轴的垂直距离为 d = 0.08 m。为使系统保持平衡，所需的弹簧力 Fspring 为：
Fspring = Mhead / d = 3.53 N·m / 0.08 m = 44.1 N
A safety factor of 1.5 is incorporated, so the spring is specified to provide at least 66 N of force. The spring wire diameter and coil dimensions were calculated using Hooke's Law, and the spring was tested to ensure no permanent deformation after 10 000 cycles.
考虑 1.5 的安全系数，因此弹簧规定至少提供 66 N 的力。弹簧线径和线圈尺寸用胡克定律计算，并经过测试确保 10 000 次循环后无永久变形。
The clamp also had to be analysed. The clamping screw converts torque applied by the user into axial force. The required clamping force of 200 N is achieved with a screw of 8 mm diameter and a trapezoidal thread, using a torque of about 2 N·m on the handle.
夹具也必须进行分析。夹紧螺钉将使用者施加的扭矩转化为轴向力。采用直径 8 mm 梯形螺纹的螺钉，手柄上施加约 2 N·m 的扭矩，就可实现所需的 200 N 夹紧力。
8. Manufacturing Processes and Assembly | 制造工艺与装配
Each component’s manufacturing process was selected to balance precision, volume, and cost. The steel arms are cut to length, bent with a press brake, and drilled using a CNC jig. Chromium plating is applied via electroplating in an automated line.
每个零件的制造工艺都经过选择，以平衡精度、产量和成本。钢臂被定长切割，用折弯机折弯，并由 CNC 夹具钻孔。镀铬通过自动化电镀线完成。
The aluminium shade is spun on a lathe from a flat disc, producing a seamless, lightweight reflector. The ABS handle and nylon bushings are injection-moulded, which allows rapid production of thousands of identical pieces per day.
铝制灯罩由平板圆碟在车床上旋压制成，形成无缝轻质的反光罩。ABS 手柄和尼龙衬套采用注塑成型，每天可快速生产数千个相同的零件。
Assembly is designed for simplicity: the arms are riveted to the pivot brackets using semi-tubular rivets, the spring hooks are snapped into place, and the wiring is routed through the hollow arms before connecting the LED driver. Each unit undergoes a final electrical safety test (hi-pot test) and a 12-hour burn-in test.
装配设计追求简便：臂杆用半空心铆钉铆接在枢轴支架上，弹簧挂钩卡入到位，电线穿过中空臂杆后再连接 LED 驱动器。每台设备都经过最终电气安全测试（耐压测试）和 12 小时老化测试。
9. Electrical Circuit and Safety Features | 电路与安全特性
The LED used is a 6 W COB (Chip on Board) module with a forward voltage of 18 V and a rated current of 350 mA. A constant-current LED driver is housed in the base clamp to convert 230 V AC mains to the required DC output. The circuit includes a bridge rectifier, smoothing capacitor, and a constant-current IC.
所用 LED 为 6 W COB（板上芯片）模块，正向电压 18 V，额定电流 350 mA。底座夹具中装有一个恒流 LED 驱动器，将 230 V 交流市电转换为所需直流输出。该电路包含桥式整流器、滤波电容和恒流集成电路。
Safety is paramount. The lamp is Class II double-insulated, meaning no earth wire is required. All live parts are enclosed, and a 3 A fuse is fitted in the BS 1363 plug. The wiring uses silicone-insulated conductors to resist heat from the LED. The shade is designed so that no user can touch the LED module, even with a 1 mm probe.
安全至关重要。该台灯为 II 类双重绝缘，无需接地线。所有带电部件均被封装，并在 BS 1363 插头中装有 3 A 保险丝。电线采用硅胶绝缘导体以抵御 LED 热量。灯罩设计使即使用 1 mm 探针也无法触及 LED 模块。
10. Testing, Evaluation and Environmental Impact | 测试、评估与环境影响
e clamping force exceeded the 200 N target consistently. Electrical testing confirmed the LED colour temperature was within ±100 K of the specified 4000 K, and the luminous flux measured 510 lm at 30 cm, exceeding the specification.
功能性测试证实，台灯在其范围内任何位置都能稳定保持，无下垂。弹簧机构运行顺畅，夹紧力稳定超过 200 N 目标值。电气测试确认 LED 色温在规定的 4000 K 的 ±100 K 以内，30 cm 处测得光通量为 510 lm，超过了规格要求。
An evaluation against the original design brief showed all requirements had been met. However, the total weight of 1.9 kg was slightly above the 1.7 kg target, suggesting that a future weight-reduction programme could investigate using thinner-gauge steel or aluminium arms.
对照原始设计简报的评估显示，所有要求都已达成。但总重为 1.9 kg，略高于 1.7 kg 的目标，这表明未来的减重计划可考虑采用更薄的钢材或铝制臂杆。
Environmental considerations were addressed by specifying recyclable materials (steel, aluminium, ABS), avoiding hazardous substances as per RoHS directives, and designing the LED to last over 25 000 hours, reducing landfill waste. The packaging uses recycled cardboard and minimal plastic.
环境方面的考虑通过以下方式处理：规定使用可回收材料（钢、铝、ABS），遵循 RoHS 指令避免有害物质，并将 LED 设计为可工作超过 25 000 小时以减少垃圾填埋。包装采用再生纸板和最少塑料。
Published by TutorHao | Engineering Revision Series | aleveler.com
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