How to Select Traction Machines for Freight Elevators in Multi-Story Factory Buildings

Abstract:In order to save land, promoting industrial operations in high-rise buildings (referred to as "Industrial Upstairs") has been a national policy direction in recent years. Based on the requirements for elevators (freight elevators) under the "Industrial Upstairs" initiative and the development trend of freight elevators in recent years, this paper puts forward viewpoints on how traction machines can better adapt to the development of large-tonnage and high-speed freight elevators, aiming to provide relevant references and assistance for elevator integral manufacturers.

Keywords:Industrial Upstairs; freight elevator; transportation efficiency; traction capacity; overload capacity; braking capacity; electromagnetic scheme; energy conservation and environmental protection

1. Domestic Trend of Factory Building Transformation

In recent years, with the continuous expansion of urban development scale, land resources have become increasingly scarce, and the supply of industrial land has been in short supply. The traditional factory development model has imposed greater pressure on enterprises to obtain space for industrial survival. At the same time, emerging industries featuring cross-border integration of high and new technologies have higher requirements for the spatial environment of production and R&D as well as factory construction standards.

Against this background, a new trend of "Industrial Upstairs" has emerged in the Pearl River Delta and Yangtze River Delta regions, where the industrial foundation is relatively developed. "Industrial Upstairs" is also known as skyscraper factories, vertical factories, or aerial factories. In essence, it refers to high-rise industrial buildings. Generally, "Industrial Upstairs" means moving production equipment with relatively light weight and low vibration to high floors to realize three-dimensional development. This concept was first proposed by Shenzhen, which relocated the R&D and production links of high-end industries such as the new generation of information technology and artificial intelligence into skyscrapers. Derived from the integration of industry and city as well as urban renewal, this model not only creates a large number of factory spaces for enterprise parks, effectively improving land plot ratio and utilization efficiency, but also forces industrial structure adjustment and enterprise transformation, alleviating the contradiction between economic development and land shortage.

Therefore, newly planned industrial park factories are usually high-rise factories with a height exceeding 24 meters or a floor count of 6 or more. Such high-rise factories require supporting high-speed and large-tonnage elevators to meet the vertical transportation needs of the factories. (The picture below shows an external view example of a modern industrial park in a certain region.)

2. Changes in Freight Elevators to Meet New Factory Requirements

To adapt to "Industrial Upstairs" and solve the vertical transportation bottleneck of high-rise industrial factories, the domestic freight elevator market has witnessed the following changes:

Changes in Freight Elevator Load Capacity

The demand for elevators with a load capacity increased from the original 2T-3T to 3T-5T, or even larger tonnages, has risen sharply. Domestic elevator enterprises have also successively obtained qualifications for 10T freight elevators. Recently, a well-known domestic freight elevator brand has launched a 42T freight elevator and obtained relevant national type test certification.

Changes in Freight Elevator Speed

The standard speed of an elevator is determined by factors such as elevator type, floor height, and load capacity. Generally, the higher the floor and the larger the load, the higher the elevator speed may be. In the past, due to the relatively low floor height of factories, the speed of most freight elevators was selected in the range of 0.25m/s - 0.63m/s. With the continuous increase in factory floor height, the lifting height of freight elevators has become higher, and the elevator speed has also been increased to 0.5m/s - 1m/s or even higher to improve transportation efficiency.

Changes in National Elevator Safety Standards

a. Several years ago, the national standard added requirements for elevator Unintended Car Movement Protection (UCMP). Freight elevator products equipped with worm gear traction machines need to be additionally equipped with rope grippers or sheave grippers to meet this standard requirement; while permanent magnet synchronous traction machines can directly use their own brakes as executive components, which further facilitates the application of permanent magnet synchronous traction machines in freight elevators.

b. The exemption for the area of car elevators has been cancelled

• In the old version of the national standard GB 7588-2003, Section 8.2.2 stipulated that the area of freight elevators could be appropriately relaxed under the condition of "effective control".

• The new version of the national standard GB 7588.1-2020 (hereinafter referred to as the "New National Standard") has deleted the exemption provision in GB 7588-2003 that allows the area of car elevators exceeding the standard under "effective control". That is, under the New National Standard, car elevators must also be configured in accordance with the area and load capacity corresponding to standard freight elevators.

• As a result, buildings that originally configured elevators for small cars at 3T (with excessive area) according to the old standard can now only be configured with elevators of 10T or above in accordance with the New National Standard.

3. Requirements for Green Energy Conservation and Environmental Protection

Permanent magnet synchronous motors feature high efficiency, energy conservation, environmental protection, and high cost-effectiveness. Compared with traditional induction motors, permanent magnet synchronous motors have higher efficiency, saving energy consumption by approximately 20-30%. This is because permanent magnet synchronous motors adopt permanent magnet excitation, which reduces leakage flux and iron loss, further improving efficiency. This high-efficiency feature is of great significance for modern industries, transportation, and other fields, as it can significantly reduce energy consumption and improve production efficiency. The author predicts that in the future, permanent magnet synchronous traction machines will continue to further occupy the market share of worm gear traction machines and become the mainstream application in freight elevators.

4. Advantages of Nidec KDS Freight Elevator Traction Machines

a. More Precise and Wide-Ranging Market Segmentation and Coverage

Nidec KDS is located in Shunde District, Foshan City, the core area of the Greater Bay Area, which is at the forefront of the "Industrial Upstairs" market. To meet the market demand for freight elevators in high-rise buildings, Nidec KDS has already fully planned a product development plan to replace the original worm gear traction machines with gearless permanent magnet synchronous traction machines as early as 2017, so as to meet the application needs of the freight elevator market. Nidec KDS freight elevator traction machine product models cover a full range from 2T to 50T, based on different traction ratios and speeds. The flexible traction ratios can meet the diverse design needs of customers, enabling them to more easily select cost-effective traction machines suitable for their applications.

Product Range of Nidec KDS Freight Elevator Traction Machines

b. Strict Design Processes to Ensure the Reliability and Safety of Design Schemes and Applications

1. Design of Traction Capacity and Wire Rope Safety Factor

Freight elevator traction machines generally adopt a traction ratio of 4:1 or even higher. In addition, the car is relatively light, which may lead to insufficient traction capacity. Therefore, it is necessary to calculate and verify based on the elevator configuration.

There are generally two solutions:

• (1) Adopt a U-shaped groove: a larger notch angle β can improve the traction capacity.

• (2) Adopt a notched V-shaped groove: it is necessary to consider the matching between the notch angle β and the groove angle γ, and the rope groove does not require hardening treatment (to reduce costs), while calculating the safety factor of the wire rope. Due to the large number of return sheaves in freight elevators, the wire rope is required to have a higher safety factor. The adoption of special groove types to meet the traction capacity, along with the change in the equivalent number of V-shaped groove traction sheaves specified in GB/T 7588.2-2020, results in a higher required safety factor for the wire rope.

2. Requirements for Braking Capacity, Overload Capacity, and Energy Efficiency

Freight elevators generally have a relatively small lifting height and low duty cycle, so they generate relatively little heat. Some people tend to design freight elevator traction machines based on passenger elevator traction machines, but such design changes will lead to a series of problems. For example, if electromagnetic materials are reduced on the basis of the original high duty cycle, it is easy to cause insufficient overload capacity and energy efficiency; alternatively, if a small-load model with a high duty cycle is used as a replacement, the shaft load, number of wire ropes, braking capacity, overload capacity, and energy efficiency may fail to meet the requirements.

Therefore, when designing freight elevator traction machines, the above factors should be evaluated, and if necessary, product development and design should be carried out again in accordance with the special requirements of freight elevator traction machines.

3. Dynamic Braking Torque

According to the requirements of type specifications and inspection regulations, when the traction machine brake serves as the deceleration component of the car upward overspeed protection device or the stopping component of the unintended car movement protection device, the elevator shall be equipped with additional braking devices. Under normal circumstances, permanent magnet synchronous traction machines adopt dynamic braking (by short-circuiting the motor windings) as a solution, but it should be noted that the electromagnetic and structural design of the traction machine should be able to withstand the impact of dynamic braking.

Due to the small amount of heat generated, freight elevator traction machines use fewer electromagnetic materials, which may lead to insufficient dynamic braking torque. In this case, the problem should be solved by increasing the air gap flux density. Under the condition of the same electromagnetic materials, the dynamic braking torque of concentrated windings is smaller than that of distributed windings, and it is more difficult to improve. Therefore, electromagnetic field finite element analysis tools need to be used to optimize the electromagnetic scheme. The dynamic braking torque of the prototype is tested through type tests, and the dynamic braking torque of mass-produced traction machines is ensured through back EMF (electromotive force) control.

4. Quality of Loading and Unloading Devices

Freight elevator traction machines have a large load capacity and require a higher shaft load than conventional traction machines, which means they need greater traction force and more wear-resistant traction sheaves during high-speed operation. The latest GB/T 7588.1-2020 stipulates that when adopting 5.4.2.2.1(b) (i.e., considering the mass of the loading and unloading device and the rated load separately), higher requirements are put forward for the traction machine's shaft load, braking capacity (especially when the brake serves as the executive component for unintended car movement protection), and traction capacity, which need to be calculated and verified independently.

c. Cost and Electromagnetic Scheme Optimization

Nidec KDS uses advanced software to conduct finite element analysis for electromagnetic field and mechanical strength design. This optimizes and enhances the strength of the traction machine, balances performance optimization with cost competitiveness, and significantly shortens the R&D cycle of the traction machine.

• Finite element analysis of electromagnetic fields

• Finite element analysis of mechanical strength

◦ Machine base

◦ Hub

To align with the national strategy of "Industrial Upstairs" and the general direction of energy conservation and environmental protection, elevator integral manufacturers adopt high-efficiency and energy-saving permanent magnet synchronous traction machines in their designs. This ensures stable and reliable performance of the integral elevator, smooth operation, high transportation efficiency, energy conservation, and environmental protection. Nidec KDS freight elevator series traction machines can cover the load requirements of freight elevators from 2T to 50T through different traction ratio schemes, with a maximum speed of up to 3m/s. They are fully capable of meeting the freight elevator transportation requirements of various industrial parks and can also provide customers with a one-stop and hassle-free selection experience. Nidec KDS has always adhered to the business philosophy of "Quality First, Customer Success". In the future market development, we will work together with customers to provide more and better solutions for "Industrial Upstairs".