Reasons why I absolutely hate mechanical operators:
1. The dangers of the gate switch. They can get inadvertently or intentionally pressed, compromising the safety system. Not all jurisdictions require DLM. Even with DLM, it can still be problematic. The lift could go out of service trapping people on upper floors who can't walk stairs, especially in high-rise apt buildings with only 2 lifts. The new-style linear ones have cabin door interlocks (no gate switch), making such situations impossible. Here's an ex. of what I'm talking about. https:/
Being able to spit the door at floor level is also bad. Pranksters are capable of manually separating the doors compromising the lock system, or sticking feet in door at final end of close cycle. This can also happen if a spring or roller is weak and the door strikes an object. This scenario can be dangerous if jumpers are left behind and no DLM installed, or case a system shutdown w/DLM. Non-splitable doors resolve this. Ex. https:/
2. With the presence of interlocks, restrictors are no longer necessary. Harmonic operators do not support cab door interlocks and many types of restrictors can easily be disabled/bypassed by mechanics compromising passenger safety. Worse yet, those electronic restrictors like hatch-latch by Adams can fail in the locked position and are prone to sensor misalignment and dead batteries during power failure. These were responsible for many fatalities at WTC on 9/11, where Othis 6940 locks were used. For this reason, they could only be released from cab top. On new installs (especially all glass), no ugly expensive sheet metal is needed between floors.
3. During entrapment, Harmonic operators can become self-locking (operator can move the doors, but doors cannot move operator). This situation requires rescue workers to have to get on the cab top and spin the infamous wheels, this can be problematic in situations where the lift is on the top floor or in the case of a steep drop (i.e train station, garage). Linear door operators never become self-locking. Once interlock is released (can be done at floor or top), door can be manually opened from both floor level and cab top. Also, if lift stalls at floor level, no triangular or drop key is needed due to the spring loaded clutch. All you gotta do is push open the door. See examples below.
Self-locking ex. GAL: https:/
Self-locking ex. MAC (0:36): https:/
Linear difference: https:/
4. Use of Harmonic operators on full glass door panels is not only more expensive due to construction costs, but a fall hazard for mechanics. Operators propped up on pedestals pose fall hazards for workers due to a steep drop from the operator to the cab top. New-style linear operators eliminate this as clutch is mounted on roller header instead of doors. This also increases installation costs as more overhead is needed. Worse yet, big money has to be spent on ulgy tackly looking sheet metal between the floors. All this is solved by Euro style linears.
These are the main reasons OEM companies stopped producing harmonic operators. They don't want to get hit by lawsuits involving their lower safety record.
I just had one change of mind about the harmonics. One advantage they have is that they do much much better on antique heavier door panels than belts. The chain drive gives better torque and reduces slip. Another is that they can be quieter on extra large openings than linear. They also don't have to relearn after power failure due to the use of cam controls. Most of these pluses only apply to very old retained equipment.
What's more interesting is that GAL just release their LWL clutch for harmonics. This greatly eliminates a lot of the aforementioned issues and replaces the gate switch w/interlock. Great step in the right direction, since there are so so many GALs in the NA market. The only two things I don't like is that it reminds of of the now obsolete Schindler QKS9 (common in AU & NZ on their M-series), which had lots of problems and that the doors are still splitable.
https:/