FI124581B - Chain elevator assembly and method for controlling a chain elevator assembly - Google Patents

Description

A chain hoist assembly and a method for controlling a chain hoist assembly

Background of the Invention

The invention relates to a chain hoist assembly according to claim 1 and to a method for controlling a chain hoist assembly according to claim 6.

The transmission of the chain hoist from the motor shaft to the hoisting chain is not smooth because the chain wheel which winds the chain is polygonal. Although the motor is rotating smoothly, there is oscillation in the chain force whose frequency 10 is directly proportional to the speed of the motor. The oscillation is greatly enhanced if the oscillation frequency of the chain force is close to the resonance frequency of the mechanics. This phenomenon, known as the polygon effect, is known in the art, and the mitigation of its adverse effects is discussed, inter alia, in US 2005/0110451. The rat-15 drive presented in that publication is based on the feedback of the sprocket position.

The problem with the above sprocket position feedback arrangement is that such a solution requires a sprocket position sensor, which is an expensive component.

BRIEF DESCRIPTION OF THE INVENTION An object of the invention is to provide a chain hoist assembly and a method for controlling a chain hoist assembly such that the disadvantages of the polygonal effect can be mitigated without the feedback of the sprocket position. The object of the invention is achieved by a chain hoist assembly and a method characterized by what is stated in the independent claims.

Preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the fact that the chain hoist assembly utilizes a chain force feedback to control the speed of the motor. The correction term for the speed control is formed

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30 multiplying the chain force variable associated with chain power by the damping factor,

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The dependence of the chain hoist assembly and method according to the invention is that the disadvantages of the polygonal effect can be mitigated without information relating to the position of the sprocket.

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BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described in connection with preferred embodiments, with reference to the accompanying drawings, in which:

Figure 1 shows a chain link 5 assembly according to an embodiment of the invention;

Fig. 2 is a diagram for controlling a speed-adjustable chain hoist assembly;

Fig. 3 is a diagram for controlling a scalar controlled chain hoist assembly; Figure 4 shows a measurement of chain force from a sprocket bearing;

Figure 5A illustrates chain force versus time in a lifting event that does not employ the method of controlling the chain hoist assembly of the invention; and

Figure 5B shows the chain force as a function of time in a lifting event using the method of the invention to control the chain hoist assembly.

DETAILED DESCRIPTION OF THE INVENTION

The chain hoist assembly shown in Fig. 1 comprises a chain 2, a chain hoisting member 4, a sprocket 6 and an adjustable speed motor 20 8 operatively connected to the chain 2 to raise the load 10 by the hoisting member 4, and lifting guide means 12.

The sprocket 6 has the shape of a five-sided polygon. The adjustable-speed motor 8 is a short-circuiting motor fed by the drive 14. The variable speed motor 8 is adapted to rotate the chain-25 wheel 6 via the gear 16.

5 In one embodiment of the invention, adjustable speed

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^ motor is a scalar controlled motor. In an alternative embodiment, the variable speed motor is a speed-adjustable motor, that is, a motor whose speed is controlled by a rotational speed | 30 loop actual feedback.

The diagram of Figure 2 illustrates the operation of the hoist control means 112 in one embodiment wherein the variable speed motor is an o speed adjustable motor 108. In this embodiment, the hoist control means 112 comprises filter means 102, damping means 104 and speed control 106.

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The filter means 102 are adapted to receive a chain force signal F representing the chain force, and to generate the chain force variable F ™ by filtering the chain power signal F. The damping means 104 are adapted to receive the chain power variable Fm and generate the angular velocity reference 5

The hoist control means 112 are adapted to receive an initial angular velocity reference cjo * mo, and to form a final angular velocity reference ω * Μ by subtracting the correction angle οο * μδ from the initial angular velocity reference ο actual value of rotation speed of the variable speed motor 108 108 The output of the speed controller 106 is a torque reference T * m that controls the drive 114. The drive 114 supplies variable speed motor 108 at ice-15. From the variable speed motor 108, a torque Tm is transmitted to the hoist mechanics 109. The hoist mechanics 109 comprise a gear, a sprocket and a chain.

Figure 3 illustrates the operation of lift control means 212 in one embodiment wherein the variable speed motor 20 is a scalar controlled motor 208. In this embodiment, the lift control means 212 comprises filter means 202, damping means 204, and scalar drive 206. Fm by filtering the chain power signal F. The damping means 204 is adapted to receive the chain power variable and form the angular frequency reference correction term οο * 5δ by multiplying the chain power variable Ffm by a damping factor o kp.

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The elevator control means 212 are adapted to receive an initial angular frequency reference jo * so,, and to form a final angular frequency reference 30 j * 5 5 by reducing the angular value formed by the damping means 204 | the haircut correction term οο * 5δ from the initial angular frequency reference ω * 5ο · The final angular frequency reference ω% is fed to a scalar controller 206 which, on the basis of § §, forms a voltage reference u * s to control the frequency converter 214. Frequency adjuster 21

From the variable speed motor 208, the torque Tm is transmitted to the lift mechanism 209. The lift mechanism 209 comprises a gear, a sprocket and a chain.

The damping factor kp depends on the frequency of vibration of the chain force. In addition, the damping factor kp may depend on the chain force or the length of the chain used for lifting the nos-5.

In one embodiment, where the damping factor kp is dependent on the frequency of oscillation of the chain force, the value of the damping factor at discrete time is calculated from n equation 10 kp (n) = kp (nX) - ^^ kp (nX), {1} ± down if fosc> flim, and n) = kp (n- \) + ^ [kp o-kp (n-1)], {2} ± up 15 if fosc ^ fiim- The term fosc is the frequency of the chain power vibration and f | im is the predetermined boundary frequency of the chain power vibration. Ts1 is the sampling interval, and Td0wn and Tup are the time constants that determine the rate of change of the damping factor. The term kp (n - 1) refers to the value of the damping factor at the 20 discrete times preceding time n.

In both the speed-adjustable embodiment of Figure 2 and the scalar-controlled embodiment of Figure 3, the chain force sampling interval Ts1 can be 10 milliseconds. If Ts 1 is substantially greater than 10 ms, the ability of the elevator control means to counteract the disadvantages of the polygonal effect is impaired.

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From the equation {1}, it is seen that, when the oscillation frequency fosc of the chain force is greater than the cut-off frequency f | im, the damping factor kp approaches zero. In an alternate embodiment of Γ1 ′ ′ 9, the damping coefficient may approach a small value other than zero. From equation {2}, in turn, it can be seen that, when the oscillation frequency fosc of the chain force ir is less than or equal to the cut-off frequency f | im,

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30 becomes a damping factor kp of a predetermined damping factor kp0.

o o Both Tdown and Tup are greater than or equal to the sampling interval o ^ TSj. Tdown is smaller than Tup. The cutoff frequency f | im can be selected by the chain hoist

the nominal speed of the configuration based on the excitation frequency fstiN, whereby for example, f | im = 1.5fstiN

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The excitation frequency ί5 «caused by the polygonal chainwheel can be calculated from the equation {3} 2π ig 5 where oom is the actual value of the angular speed of the variable speed motor, N is the number of sides of the polygon and ig is the gear ratio. The nominal frequency excitation frequency ί5 «Ν of the chain hoist assembly is obtained from equation {3} by placing the variable speed motor angular speed actual com at its 10 nominal angular velocity.

The mechanical resonance frequency of the chain hoist assembly is obtained from the equation f „, = '{4} 2π V m 15 where kCha is the spring constant of the chain and m is the mass of the load. The spring constant of the chain is given by = ^. {5} h 20 where E is the elastic modulus of the chain, Ar is the effective surface area of the chain and h is the length of the chain from the sprocket to the lifting member. One chain with a nominal load of 500 kg has an effective surface area of 36.2 mm2 and a modulus of elasticity of 24329 N / mm2 $ 2 A polygonal effect is observed when the excitation frequency fst is close to the mechanical resonance frequency fres of the chain hoist assembly. At its worst, the oscillation caused by the polygonal effect is when fstj = fres.

$ £ The periodic oscillation period tosc of the chain force oscillation can be determined, for example, by the zero crossing points of the bandpass filtered chain power signal. The bandpass filtering can be implemented in the embodiment of Fig. 2 by the filter means 102 and in the embodiment of Fig. 3 by the filter means 202. The use of these {1} and {2} coefficients is the inverse number of chain power oscillation timescc, fosc = 1 / t0Sc

The filter means of the chain hoist assembly according to the invention are preferably adapted to high-pass filtering the chain power signal F. The high-pass filtering of the chain power signal can prevent problems otherwise caused by the chain power feedback to control the motor speed. Also, band pass filtering of the chain power signal F can be used. One skilled in the art will appreciate that bandpass filtering includes high-throughput filtering. Below are examples of high-pass filtering and band-pass filtering of a chain power signal.

To high-pass filter the chain power signal, a low-pass filtered chain power signal Fipf is first generated as a digital filter.

10 F | pf (n) = F | Pf (n - 1) + Tsiaipf [F (n) - F | pf (n - 1)] {6}

In equation {6} Τ5, there is a sampling interval and aiPf is the bandwidth of the low pass filter. Index n refers to the discrete point in time under consideration, and index n - 1 refers to the point preceding the current point in time. The bandwidth aiPf of the ali-15 pass filter is selected such that aiPf <2πίΓβ5. Subsequently, the unfiltered chain power signal F is averaged by generating a high-pass filtered chain power signal FhPf by means of a low-pass filtered chain power signal FiPf.

20 FhPf (n) = F (n) - Fipf (n) {7}

If the high-pass filtered chain-power signal Fhpf has high-frequency noise, it can still be filtered by a low-pass filter having a bandwidth ciipf2 significantly greater than the mechanical resonance frequency fres of the chain hoist assembly. The end result is a band-pass filtered circuit power signal FbPf. δ

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Fbpf (n) = Fbpf (n - 1) + TsjOiipc [Fhpf (n) - Fbpf (n - 1)] {8} cp

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In the chain hoist assembly of the invention, the chain force can | for example, between the lifting member and the chain. A conventional strain gauge sensor may be used for measurement. In a chain hoist assembly which is adapted to be suspended from the ceiling, the chain force can be measured indirectly from the point of suspension. Here, the chain force is obtained as the difference between the force measured at the point of attachment and the known force due to the dead weight of the chain hoist assembly.

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Alternatively, the chain force can be measured from the sprocket bearing as shown in Figure 4. Figure 4 shows that the strain gauge sensor 502 is glued to the underside of the bearing housing 504. Bearing inner periphery 506 is rotatable with respect to bearing housing 504. The chain wheel shaft of the chain hoist assembly is mounted within the bearing inner ring 506 such that the chain wheel rotates together with the bearing inner ring 506 while the bearing housing 504 remains stationary.

When measuring the chain force from the sprocket bearing as shown in Fig. 4, the output signal of the strain gauge sensor 502 may contain a harmful amount of interference. For example, due to 10 parasitic coupling, pulse width modulated motor voltage can cause high frequency interference to the strain gauge sensor output signal. High frequency interference caused by pulse width modulated motor voltage can be reduced by adding ferrite rings around the motor supply cables.

In embodiments where the chain force is measured from the bearing wheel bearing 15, it is useful to pay attention to the frequency and magnitude of the resulting disturbances when selecting the bearing. In particular, it is advisable to avoid a situation where the disturbances caused by the bearing balls or rollers are of such a frequency that they cannot be properly filtered from the output signal of the force measuring sensor.

Figures 5A and 5B illustrate the effect of a chain lift assembly control method of the invention on chain force. Fig. 5A shows the chain force FCh1 as a function of time in a lifting event which does not employ the method of controlling the chain hoist assembly according to the invention. Figure 5B shows the chain force FCh2 as a function of time in a lifting operation using the method of controlling the chain hoist assembly according to the invention.

In both the lifting event of Figure 5A and the lifting event 5 of Figure 5B, a 1000 kg load is lifted from the ground to a height of 6 meters. FIGURES

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The vertical axis of ^ 5A and 5B is in kilonewton, and the horizontal axis in °. The lifting events utilized a short circuit motor chain link assembly. In the lifting operation of Fig. 5B, a short-circuit motor is driven was omitted by the scalar control method according to the invention, in which the chain force variable is used to form a correction term for the angular frequency reference, o § Comparing Figures 5A and 5B, it will be seen that

the chain force FChi oscillates much more strongly than in Fig. 5B

00 35 the chain force FCh2- The polygonal effect is most clearly reflected in the chain force FChi for the time interval t = 10 ... 16s.

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As stated above, the adjustable speed motor of the chain hoist assembly of the invention may be, for example, a short-circuit motor fed by a frequency converter. One skilled in the art will appreciate that instead of an asynchronous motor, a synchronous motor can be used quite well. Generally, a variable speed motor can be any motor whose speed can be controlled with sufficient precision. The variable speed motor may thus be other than an electric motor.

One of ordinary skill in the art will understand the similarity between the angular velocity of the velocity adjustable embodiment of Figure 2 and the angular frequency of the scalar-controlled embodiment 10 of Figure 3. To describe the common features of the speed adjustable embodiment and the scalar controlled embodiment, the term angular variable is used herein to refer to both angular velocity and angular frequency. Thus, the term initial angular reference refers to both the initial angular frequency reference ω * 5ο of the scalar controlled embodiment and the initial angular velocity reference u * mo of the scalar-controlled embodiment, respectively. to the final angular frequency reference ω * 5 of the scalar controlled embodiment and to the final angular velocity reference ω * Μ of the velocity controlled embodiment.

For the sake of simplicity, the chain force signal F in this text is assumed to be a signal directly proportional to the chain force. One skilled in the art will appreciate that, for example, when the text refers to filtering the chain power signal, this effectively means filtering the measured values of the chain power. The chain force variable Fm 5 to be generated from the chain power signal is a variable that describes the actual value of the chain force in a usable manner

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^ for the purpose of generating a correction term for an angle measure.

° The initial angular guide may be a user-provided instruction on lifting speed as such. Alternatively, a preliminary angular guide may be a limited instruction formed on the basis of a user's instruction regarding lifting speed. Limitation of the initial angular guide may be necessary to avoid, for example, the stresses and / or damages that too high speed variations desired by the user may cause the chain hoist assembly.

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The lift control means can be implemented programmatically. For example, in the embodiments of Figures 2 and 3, the elevator control means are part of the software of the respective drive.

In Figure 1, the lifting member 4 is a lifting hook. In alternative embodiments of the invention, the lifting member may be any load securing member, such as a lifting anchor, a lifting fork, or a magnetic lifting member.

It will be obvious to a person skilled in the art that the basic idea of the invention can be implemented in many different ways. The inventions, therefore, are not limited to the examples described above, but may vary within the scope of the claims.

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Claims (8)

A chain lift assembly comprising a chain (2), a lifting member (4) connected to the chain, a sprocket (6) and a motor (8; 108; 208) of adjustable speed, which motor is via the sprocket (6) functional joined to the chain 5 (2) for lifting a load (10) by means of the lifting means (4), and the elevator controls (12; 112; 212) arranged to receive a preliminary angular magnitude instruction (ω * Μ0; ω * 5θ); form a correction term (ω * ΜΔ; ω * 5Δ) for the angular magnitude instruction; Form a final angular magnitude instruction (ω * Μ; ω * 5) by using origin data including the preliminary angular magnitude instruction (ω * Μο; ω * 5θ) and the correction term (ω * ΜΔ; ω * 5Δ) for the angular magnitude instruction; controlling the rotational speed of the motor (8; 108; 208) at an adjustable speed by means of the final angular magnitude instruction (ω * Μ; ou * s); characterized in that the elevator controls (12; 112; 212) are further arranged to receive a chain power signal (F) representing chain power; form a chain power variable {Fm) using the chain power signal One (F); form the correction term (οο * μδ; ω * 5Δ) of the angular magnitude instruction by multiplying the chain force variable {F m) by an attenuation coefficient (kp) which is a magnitude dependent on the oscillation frequency (fosc) of the chain power signal; and changing the value of the attenuation coefficient (kp) as a function of the oscillation frequency (fosc) of the chain power signal (F) in the way that the oscillation frequency (fosc) of the chain signal is higher than a predetermined boundary frequency. (f µm), approaches the attenuation coefficient (kp) zero or a predetermined 0 ^ value for the attenuation coefficient, and the oscillation frequency (fosc) of the chain power signal (F) is lower than the predetermined limit frequency (f µm) when - is the damping coefficient (kp) of the predetermined g reference value (kp0) of the damping coefficient, which is substantially higher than said predetermined position o value of the damping coefficient. O) § 2. Chain elevator assembly according to claim 1, characterized in that the elevator controls (12; 112; 212) comprise filter means (102; 202) 14 arranged to filter chain power signal (F) to form the chain power variable (Ffiit). . Chain elevator assembly according to claim 1 or 2, characterized in that the elevator controls (12; 112; 212) are arranged to determine the oscillation frequency (fosc) of the chain power signal (Fc) on the basis of the points of the chain power variable (Ffm). exceeded. Chain elevator assembly according to any of claims 1 to 3, characterized in that the motor at an adjustable speed is a scalar-controlled motor (208), the preliminary angle magnitude instruction being a preliminary angular frequency instruction (ω * 5θ), the angular frequency instruction correction term and the final angular magnitude instruction is a final angular frequency instruction (ω * 5θ) · Chain elevator assembly according to any one of claims 1 to 3, characterized in that the motor with adjustable speed is a variable speed motor (108), the preliminary angular speed instruction (ω * Μο), the angular speed instruction's correction speed of the angular speed instruction μδ) and the final angular magnitude instruction is a final angular velocity instruction (ω * Μ). 20 A method of controlling a chain elevator assembly comprising a chain (2), a lifting member (4) connected to the chain, a sprocket (6) and a motor (8; 108; 208) at an adjustable speed, said motor being via the sprocket ( 6) functionally connected to the chain (2) for lifting a load (10) by means of the lifting means (4), in which method a preliminary angular magnitude instruction (ω * ωο; ω * 5ο) is received; a correction term (οο * μδ; ω * 5Δ) is formed for the angular magnitude instruction; c \ j ^, a final angular magnitude instruction (ω * Μ; ω * 5) is formed by using the origin data that includes the preliminary angular magnitude instruction (ω * Μο; ω * 5θ) and the correction term (ω * ΜΔ; ω * 5Δ) for the angular magnitude instruction; ^ the speed of rotation of the motor (8; 108; 208) is controlled at an adjustable o speed using the final angular magnitude instruction (ω * Μ; ou * s); o wherein the method is known in that it further comprises the steps of receiving a chain power signal (F) representing chain power; A chain power variable (Fm) is formed using the chain power signal (F); the correction term (ω * ΜΔ; ω * 3Δ) of the angular magnitude instruction is formed by multiplying the chain force variable (F ™) by an attenuation coefficient (kp) which is a magnitude dependent on the oscillation frequency (fosc) of the chain power signal; and the value of the attenuation coefficient (kp) is changed as a function of the oscillation frequency (fosc) of the chain signal (F) in the way that the oscillation frequency (fosc) of the chain force signal (F) is higher than a predetermined limit frequency (f kp) zero or a predetermined low value of the attenuation coefficient, and since the oscillation frequency (fosc) of the chain power signal (F) is lower than the predetermined threshold frequency (f), the attenuation coefficient (kp) approaches the attenuated coefficient (predetermined reference value) than said predetermined low value of the attenuation coefficient. The method according to claim 6, characterized in that it further comprises a step of filtering the chain power signal (F) to form the chain power variable (Ffiit). 8. A method according to claim 7, characterized in that the oscillation frequency (fosc) of the chain power signal (F) is determined on the basis of the points of the chain variable (F F) where zero is exceeded. CO δ C \ J i o CD X cc CL o o o O) o o C \ l