Field of the invention

This invention concerns a tunable mass damper for a conveyor drive machine.

Background

Elevator hoisting machine may induce vibrations while running. Vibrations may cause noise, sometimes exceeding the allowable noise levels. This may have an effect on elevator ride comfort. Noise may also be conducted to the nearby apartments in the building.

Use of a mass damper based on wire damping technology has been disclosed in patent document FI20135610. This damping device is sensitive to any tuning errors or other unidealities, because it has a narrow frequency range for damping. Consequently, the damping device has narrow operating range, which complicates tuning of the device .

Summary

This invention represents a solution for reducing vibration of a conveyor drive machine, such as an elevator hoisting machine. Therefore a tunable mass damper device is provided, which can be fixed to a conveyor drive machine for damping vibrations and noise. The inventive device has wider operating range, which makes tuning easier in real-world applications.

First aspect of the invention is a tunable mass damper device, comprising a shaft and a vibrating body. The vibrating body comprises a frame, a first plate extending from the frame concentrically about the shaft and a second plate extending from the frame concentrically about the shaft. The vibrating body further comprises a stack of elastic friction plates placed between the first plate and the second plate and fixed to the shaft and to the frame of the rotating body. The stack of friction plates are clamped together to cause friction between the adjacent friction plates when vibrating. The shaft comprises fixing element or fixing means, such as threads, for fixing the vibrating body to a frame of a conveyor drive machine.

The first plate and the second plate are preferably elastic plates.

Second aspect of the invention is conveyor drive machine, comprising the mass damper device of the first aspect fixed to the conveyor drive machine frame.

The conveyor drive machine may be door operator of an automatic door or a drive machine of an escalator or a moving walk.

Alternatively, the conveyor drive machine may be an elevator hoisting machine, having the mass damper device fixed to the hoisting machine frame.

The hoisting machine preferably comprises a hoisting machine brake fixed to the frame of the hoisting machine. The mass damper device may be fixed to the hoisting machine frame in the immediate vicinity of the hoisting machine brake.

Third aspect of the invention is an elevator comprising the elevator hoisting machine of second aspect.

According to an embodiment, the elevator comprises an elevator car and / or a counterweight movable in an elevator hoistway, as well as a guide rail for guiding movement of the elevator car and / or the counterweight, respectively. The elevator hoisting machine is arranged in the hoistway, in the space between the guide rail and the hoistway wall.

Fourth aspect of the invention is a retrofit kit for onsite installation to a frame of an existing conveyor drive machine. The retrofit kit comprises the mass damper device according to the first aspect.

Fifth aspect of the invention is a method for reducing vibrations in a conveyor drive machine by using mass damper device of the first aspect. The method comprises:

- measuring, by a microphone, a noise response of a conveyor drive machine,

- determining a desired natural frequency of the mass damper device based on the noise response, and

- tuning natural frequency of the mass damper device towards the desired natural frequency by adjusting mass, such as number of plates, preferably elastic plates, of the vibrating body.

Detailed description of the invention

In the following, embodiments of the invention will be discussed with reference to the following drawings:

Fig. 1 illustrates schematically mass damper attachment to a prime system, in particular to an conveyor drive machine according to an exemplary embodiment of the invention .

Fig. 2 represents cross-sectional view of a mass damper device according to an exemplary embodiment.

Fig. 3 represents oblique top view of cross section of mass damper device according to an exemplary embodiment.

Fig. 4 represents an exemplary damping response of a mass damper device in a damping arrangement of fig. 5.

Fig. 5 shows a damping arrangement of an elevator hoisting machine according to an exemplary embodiment.

Fig. 6 represents an oblique top view of a vibrating body of a mass damper device according to an exemplary embodiment .

Fig. 7 represents a side view of the vibrating body of Fig. 6.

Fig. 8 represents a friction plate of a mass damper device according to an exemplary embodiment.

Same reference numbers are used for similar items throughout the drawings .

A conveyor drive machine, such as an elevator hoisting machine induces vibrations while running. Such vibrations cause noise, sometimes exceeding the noise limitation requirements. The embodiments shown hereinafter disclose a tuned mass damper developed to reduce vibrations and the resulting noise. By means of the mass damper device according to the invention, peak noise of the elevator hoisting machine may be reduced by 5 to 10 dB at resonance frequency.

Based on the measurement tests, by using mass damper with internal friction damping according to the exemplary embodiments disclosed a much wider frequency band may be obtained compared to prior art solutions. In addition, a mass damper device which is simpler, considerably cheaper and easier to manufacture is achieved .

Fig. 1 illustrates schematically attachment of a mass damper device to a conveyor drive machine frame 1 (prime system) . Such a conveyor drive machine may be an elevator hoisting machine, or a drive machine of an escalator or a moving walk.

The conveyor drive machine has a resonant frequency, where the noise peak usually appears. Idea behind a mass damper is to adjust natural frequency of the mass damper device to be close to resonant frequency of the system. When the drive machine frame 1 is vibrating at the excitation frequency, it will be resonating the vibration to the mass damper device which starts vibrating at the same frequency and damps the vibration of the conveyor drive machine.

The mass damper device of fig. 1 has a shaft 2 and a vibrating body 3 fixed concentrically to one end of the shaft 2. The other end of the shaft 2 is provided with threads. The mass damper device is fixed to the frame 1 of a conveyor drive machine by screwing it down to a hole in the frame 1.

Fig. 2 represents cross-sectional view of the mass damper device of fig. 1, whereas fig. 3 represents oblique top view of cross section of the same mass damper device. The vibrating body 3 of the mass damper device comprises a frame 6 made of stacked steel rings. The frame surrounds the shaft 2. The vibrating body 3 further comprises a first elastic, disc-shaped steel plate 5 extending from the frame 6 concentrically about the shaft and towards the shaft 2. It also comprises two second elastic plates 8 both extending from the frame 6 concentrically about the shaft 2 and towards the shaft 2.

In addition, the vibrating body 3 comprises a stack 4 of elastic friction plates in the form of steel plates fixed to the shaft 2 and to the frame 6 and placed between the first elastic plate 5 and the second elastic plate 8. The stack of friction plates are clamped together to cause friction between the adjacent friction plates when vibrating. The second elastic plates 8 are arranged closer to the friction plate stack 4 than the first elastic plate 5. An additional ring mass 7 is fixed at the end of the frame 6. Steel plates 4, 5, 8 and ring mass 7 are fixed to the frame 6 by means of bolts .

The friction between the plates increases damping factor of the mass damper device, widening the operating range of the device.

Finally, the shaft 2 comprises threads for fixing it to a frame 1 of a conveyor drive machine.

In the following, operation of the mass damper device will be discussed in connection with of an elevator hoisting machine.

If mass damper does not have damping, the excitation frequency of the prime system must match accurately to the natural frequency of the damper. By adding damping to the system, we are able to increase the frequency band, where the damper works . A wide band was obtained by using internal friction method in the mass damper, see Figure 2. This method works by adding thin metal plates one on the other. When the prime system is resonating the vibration to mass damper, the mass damper starts to vibrate as well and the movement of these thin plates causes friction between the surfaces which cases the damping system.

Fig. 4 shows motor noise testing results for a speficic NMX07 hoisting machine. The test arrangement is shown in fig. 5. Noise of the hoisting machine was measured by means of a microphone by driving the elevator without the tuned mass damper in order to map the initial situation. After that the tuned mass damper was attached to the hoisting machine and after running the results were compared. A mode analysis of the software did not exactly match with the actual values, so a hammer test was carried out to determine the correct natural frequency of the prototype. Mass of the prototype was adjusted according to the hammer test and thus the correct natural frequency was obtained for the prototype. Engine testing was then performed with the re-adjusted prototype.

Vibration attenuation and noise peak reduction were successful and the greatest effect was experienced with the reduction of the noise peak at 235 Hz resonant frequency with speed of 1,04 - 1,05 m/ s . The effect of the tuned mass damper also extended to a wider range. The noise peak at the resonant frequency decreased around 10 dBA. The motor tests were started by measuring a noise pressure levels of the hoisting machine in excitation frequencies at first by not using a mass damper. After the initial noise levels were measured (blue curve in Figure 4. ) , a mass damper with wire rope damping method was attached to frame2 of the NMX07 hoisting machine and measurement test was repeated to obtain results of that damping method. In fig. 5, frame 2 it the frame part fixed to guide rail 9. As it can be seen from Figure 4 (orange curve) , the mass damper worked well in specific frequency, but the frequency band where the damper worked was narrow. After that we tested a mass damper with internal friction damping method to obtain wider functional band. The results were great and much wider functional band was obtained (grey curve in Figure 4. ) .

Fig. 6 represents an oblique top view of the vibrating body of a mass damper device according to figures 1 - 3. Fig. 7 represents a side view of the same vibrating body .

Figure 8 shows elastic friction plates of the stack 4. By clamping the plates tightly one on the other, friction losses will be generated during vibration. These friction losses will cause wider functional frequency band for the mass damper device.

It is obvious for a skilled person that the mass damper device as disclosed above may be used as an accessory, such as a retrofit kit, for conveyor drive machine installations to fulfill noise cancellation requirements .

In addition to the elevator application, the mass damper device according to the invention is applicable for escalator drive machines, moving walk drive machines or drive machines of an automatic doors (i.e. door operators) .

The specific examples provided in the description given above should not be construed as limiting the applicability and/or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.