Application of Electromagnetic Clutches in Shuttleless Looms
1. Overview
The electromagnetic clutch applied in shuttleless looms is a special-purpose clutch categorized under single-plate clutches, which was developed synchronously with shuttleless looms starting from the late 1980s. This product mainly includes combined clutch (integrated clutch-brake unit), electromagnetic brake, electromagnetic clutch and electromagnetic jaw clutch. All its specifications, parameters, performance, mounting dimensions, starting/braking torque (dynamic torque), transmitted torque (static torque) and other performance indicators are designed to meet the operational requirements of shuttleless looms. It is mainly manufactured by world-renowned professional clutch manufacturers including WARNER Electric (USA), KEB (Germany), Miki Pulley (Japan) and ZF Friedrichshafen AG (Germany).
This product successfully applies the structural theory of multi-plate electromagnetic clutches to loom-specific electromagnetic clutches, optimizes the traditional structure of single-plate clutches and improves the structural performance of dedicated loom clutches. The upgraded performance fully satisfies the special operating demands of shuttleless looms. Unlike general-purpose clutches that are produced in complete series, this type of special clutch is non-serialized and continuously upgraded iteratively alongside the technological evolution of shuttleless looms. The high speed, high efficiency and high reliability of modern new-type shuttleless looms are inseparable from the progress of dedicated loom clutches, which have evolved into an independent new branch within the single-plate electromagnetic clutch product family.
2. Structural Characteristics of Clutches for Shuttleless Looms
Loom-dedicated clutches need to fulfill comprehensive performance requirements of shuttleless looms in terms of installation, commissioning, maintenance, high transmitted torque, high starting and braking torque, as well as rapid engagement (quick startup) and rapid disengagement (emergency stop).
Air-jet looms and water-jet looms bear relatively light loads; they rely on high-starting-torque motors for rapid acceleration and electromagnetic brakes for fast braking and stopping. Projectile looms feature low inertial resistance from projectile grippers, so they adopt the same scheme as air-jet and water-jet looms, i.e., direct drive by high-performance starting motors. The special clutches equipped on these three types of shuttleless looms are all modified variants of single-plate electromagnetic clutches.
For rapier looms, electromagnetic clutches are adopted for frequent in-operation quick startups to avoid excessive motor on-off cycling, while electromagnetic brakes execute rapid main machine stopping. To realize both instant startup and immediate halt, compact common armature combined clutch-brake units are universally configured. Such equipment covers multiple mainstream rapier loom models: SM92, SM93, TM-11, TM-11E manufactured by SOMET (Italy); GTM, GTM-A, GTM-AS from PICANOL (Belgium); HTV-1/E, HTV-M/E produced by DORNIER (Germany); ISL-888Ⅱ by Ishikawa (Japan); P400 and P400S by SAPA (Spain), all fitted with compact common armature combined clutch-brake assemblies.
To adapt to wider weaving widths and higher operating speeds, the torque rating of loom-specific clutches has been correspondingly increased via two technical solutions:
Solution 1: Single magnetic circuit with enlarged radial dimension of friction pairs
The torque boost is achieved by expanding the radial size of friction discs within a single magnetic circuit. For instance, the clutch of SOMET SM92 rapier loom is radially enlarged to meet the higher torque demand of TM-11E model. Non-metallic friction linings can be adopted as friction pairs for this structure; the friction pairing between non-metallic pads and metal counterparts delivers an extended service life. Since the service life of clutches depends on the durability of friction pairs, and the overall reliability of shuttleless looms is determined by the lifespan of core basic components, increasing the friction disc diameter via the single magnetic circuit method essentially enhances the operational reliability of shuttleless looms.
Solution 2: Dual magnetic circuit structure for limited radial installation space
Restricted by the overall structural dimensions of looms where radial enlargement is impossible, the dual magnetic circuit clutch structure is developed based on the flux repeated penetration principle of multi-plate electromagnetic clutches, which drastically raises the torque output to match the upgraded load requirements of high-speed looms. However, the magnetic flux passes through friction plates twice in the dual magnetic circuit design, which mandates the use of all-metal friction pairs. The high wear rate of metallic friction pairs shortens service life and consequently reduces the overall reliability of shuttleless looms.
Typical looms equipped with dual-magnetic-circuit common armature combined clutch-brakes include FAST rapier looms by SMIT, GTM-A/GTM-AS rapier looms by PICANOL, and HTV-1/E/HTV-M/E rapier looms by DORNIER. In addition, the brake assembly on PICANOL's latest DELTA air-jet loom and the electromagnetic clutch on SMIT FAST rapier looms both adopt dual magnetic circuit friction pairs, which deliver higher torque without increasing the radial outer diameter of friction discs.
Positioning electromagnetic clutches are mandatory for slow-speed weft finding operations. Low operating speed during weft finding generates large transmission torque, hence positioned jaw clutches are required for this working condition. Traditionally, positioning is realized via locating pins combined with equidistant meshing teeth to complete the slow weft-finding movement. This structure is applied to the slow weft-finding clutches of PICANOL GTM rapier looms and SOMET TM-11 rapier looms.
In recent years, non-equidistant meshing teeth have replaced equidistant teeth to simplify manufacturing processes, facilitate installation and debugging, and improve the reliability of jaw clutches, which are used on the jaw clutches of PICANOL GTM-A and GTM-AS rapier looms. To cut energy consumption and reduce clutch heat generation, all slow weft-finding jaw clutches adopt power-off engagement & power-on disengagement (normally engaged when de-energized) control logic. This control mode is adopted on the weft-finding clutches of SOMET TM-11, PICANOL GTM/GTM-A/GTM-AS and SMIT FAST rapier looms.
3. Development of Clutches for Domestic Shuttleless Looms
With the technology introduction, independent research and localized development of shuttleless looms, China has achieved domestic production of dedicated clutches for all types of shuttleless looms. Nevertheless, the industry started late, faces fierce market competition and suffers from scattered small-scale manufacturers, failing to form large-scale branded production clusters.
Driven by the demand for indigenous R&D of shuttleless looms and under a standardized competitive market environment, large-scale centralized branded production is expected to take shape in the near future, enabling domestic products to enter the global market and align with international standards. At present, domestic special clutches for shuttleless looms are still in the reverse engineering stage, with noticeable gaps in material performance and manufacturing precision compared with world-class overseas manufacturers. It is predictable that domestic loom clutch production will gradually phase out simple imitation and step into independent innovation and development, forming large-scale centralized branded production systems to support the sustainable upgrading of China's shuttleless loom industry.
