The invention relates to a method to estimate a load behavior in a laundry treatment machine. Furthermore, the invention relates to a laundry treatment machine with a control unit to estimate a load behavior. For example, the laundry treatment machine is a washing machine or a drying machine or a combined washing and drying machine.

The estimation of a load inertia at the beginning of a washing cycle has a key role to set the amount of resources such as water, detergent, bleach and softener and the amount of energy in order to achieve a good washing performance without wasting resources and energy. The load inertia is caused by the laundry within the drum of the laundry treatment machine and varies in a wide range.

The washing unit is suspended to the cabinet by a set of springs and dampers. This mechanical system is adjusted to have a resonance frequency at a relatively low angular speed between 150 rpm and 300 rpm. During the spinning phase, the angular speed of the drum has to cross this resonance region without interference between the tub and the cabinet. Due to an increase of the drum size and a loading capacity of the laundry treatment machine the available space between the tub and the cabinet decreased. As a consequence, a precise estimation of a load unbalance is required in order to avoid a mechanical impact between the tub and the cabinet when the resonance region is crossed.

US 2005/204482 A1 discloses a method to estimate a load inertia and a load unbalance. The estimation is based on an angular speed signal and a torque signal during an acceleration of the drum or during superimposition of a dither signal to a substantially constant angular speed in order to excite the mechanical system of the laundry treatment machine.

EP 2 607 535 A2 discloses a method of operating a laundry treating appliance comprising at least one cycle of operation controlling the extraction of liquid from the laundry load on the basis of the inertia of the laundry load. US 2019/0112745 A1 discloses a method of operating a laundry washing machine.

It is an object of the present invention to provide a method to estimate a load behavior in a laundry treatment machine in an easy, reliable and accurate manner.

This object is achieved by a method comprising the steps of claim 1. According to the inventive method the inertia and the load torque is determined based on two operations of the laundry treatment machine with two different speed controller parameters and bandwidths of the speed controller. The speed controller regulates the angular speed of the drive motor an is part of the speed control loop. The first operation can be described by $$-{\widehat{T}}_L+T_{\mathit{em}}^{\ast 1}={\widehat{J}}_t\widehat{{\dot{\omega }}^1}$$ and the second operation can be described by $$-{\widehat{T}}_L+T_{\mathit{em}}^{\ast 2}={\widehat{J}}_t\widehat{{\dot{\omega }}^2}$$ wherein
$T_{\mathit{em}}^{\ast 1}$  denotes the first torque signal,
$\widehat{{\dot{\omega }}^1}$  denotes the derivative of the first angular speed signal,
$T_{\mathit{em}}^{\ast 2}$  denotes the second torque signal,
$\widehat{{\dot{\omega }}^2}$  denotes the derivative of the second angular speed signal,
T̂_L  denotes the load torque and
Ĵ_t  denotes the total inertia of the laundry treatment machine with regard to a rotation around the rotational axis.

Based on equations (1) and (2) the total inertia can be evaluated by $${\widehat{J}}_t=\frac{T_{\mathit{em}}^{\ast 1}-T_{\mathit{em}}^{\ast 2}}{\widehat{{\dot{\omega }}^1}-\widehat{{\dot{\omega }}^2}}$$

The load inertia can be evaluated by $${\widehat{J}}_L={\widehat{J}}_t-J_m$$ wherein

Ĵ_L

denotes the load inertia and

J_m

denotes the inertia of the laundry treatment machine.

The inertia J_m of the laundry treatment machine is known from construction data or can be measured by running a test without a distributed load inside the drum.

Furthermore, in case that the load inertia is evaluated according to equation (4), the load torque can be determined, for example according to equation (1) and/or equation (2) and/or by means of a load observer as soon as the total inertia Ĵ_t is estimated according to equation (3) and the load torque observer is parametrized accordingly.

The load torque observer enables an accurate and continuous estimation of the load torque. The load torque observer can be easily implemented into a control unit of a laundry treatment machine. Additional hardware components, like sensors, are not required.

The advantages of the inventive method are as follows:
The load inertia and the total inertia can be evaluated at a constant angular speed, for example at 100 rpm, in order to avoid the use of an acceleration ramp and to avoid the risk of a mechanical impact between the tub and the cabinet. The same applies for the estimation of a load unbalance based on the load torque. The method can be used to estimate the dry load at the beginning of the washing cycle without using an acceleration ramp in order to set the amount of resources and energy. In case of a combined washing and drying machine or a drying machine the inertia estimation can be used to stop the drying cycle at a desired moisture retention. Furthermore, the inventive method can be used to estimate the wet load at the end of the washing cycle without using an acceleration ramp. The estimated load torque and an estimation of the load unbalance based thereon can be automatically adapted with the estimated total inertia. The inventive method can be used in a laundry treatment machine with a large drum and can be easily implemented in existing control units. The estimation of the inertia and/or the load torque is not affected by friction or by the speed controller setting. Furthermore, the estimation of the inertia and/or the load torque just requires an operation of the laundry treatment machine at a constant angular speed without the need of an acceleration ramp such that the inertia and/or the load torque can be estimated in an easy and quick manner.

A method according to claim 2 ensures an easy, reliable and accurate estimation of the load behavior. The desired angular speed or the target speed is constant. The resulting speed fluctuations or speed oscillations depend on the bandwidth of the speed controller and/or on the controller parameters of the speed controller, on the mass of the load and on the total inertia. A change of the speed controller parameters that changes the bandwidth of the speed controller at a constant desired angular speed results in a change of the speed oscillations and of the drive torque. The angular speed oscillations about the constant desired angular speed could be, as example, within +- 10 rpm, or within +- 5 rpm, or within +- 2 rpm.

A method according to claim 3 ensures an easy, reliable and accurate estimation of the load behavior. The mass of the load can be estimated in an easy and accurate manner depending on the load torque. The unbalance mass can be estimated by $$\widehat{m}=\frac{\max \left({\widehat{T}}_L\right)}{g\cdot r}$$ wherein

m̂

denotes the mass of the load which corresponds to the unbalance mass,

max(T̂_L)

denotes the maximum of the load torque,

g

denotes the gravitational acceleration and

r

denotes the drum radius.

A method according to claim 4 ensures an easy, reliable and accurate estimation of the load behavior. The angular load position can be estimated by solving $${\widehat{T}}_L=-\widehat{m}gr\sin \left(\widehat{\Theta }+\widehat{\sigma }\right)$$ wherein

Θ̂

denotes the angular drum position in relation to a reference position,

σ̂

denotes the angular relative load position inside the drum,

T̂_L

denotes the load torque,

m̂

denotes the mass of the load which corresponds to the unbalance mass,

g

denotes the gravitational acceleration and

r

denotes the drum radius.

The angular load position can be described by $$\widehat{\alpha }=\widehat{\theta }+\widehat{\sigma },$$ wherein

• α̂ denotes the angular position of the load in relation to the reference position
• such that $${\widehat{T}}_L=-\widehat{m}gr\cos \left(\widehat{\alpha }\right)$$
• since the load torque has a maximum value, if α̂ = 90°.

A method according to claim 5 ensures an easy, reliable and accurate estimation of the load behavior. The total inertia can be easily estimated according to equation (3). Furthermore, the load inertia can be easily estimated according to equation (4).

A method according to claim 6 ensures an easy, reliable and accurate estimation of the load behavior. The signals are transformed into a frequency domain, in particular by computing a Fourier Transformation (FT). This transformation enables to determine respective first harmonics of the signals. The first harmonics are used for the subsequent determination of the inertia and/or the load torque. The determination of the inertia and/or the load torque is not affected by noise signals. The first harmonics comprise information about the frequency, the amplitude and the phase of the signals. At least one of the frequency, the amplitude and the phase are used for the subsequent estimation of the inertia and/or the load torque.

A method according to claim 7 ensures an easy, reliable an accurate estimation of the load behavior. By using the first harmonics of the signals the estimation of the inertia and/or the load torque is not affected by noise signals. The first harmonics of the signals are calculated for example by a Fourier Transformation (FT). The first harmonics comprise information about the frequency, the amplitude and the phase of the signals. At least one of the frequency, the amplitude and the phase are used for the subsequent estimation of the inertia and/or the load torque.

A method according to claim 8 ensures an easy, reliable and accurate estimation of the load behavior. The angular position and/or the drive torque of the drive motor can either be measured or estimated. The angular position is used to calculate an observer error.

A method according to claim 9 ensures an easy, reliable and accurate estimation of the load behavior. The observer error is used to estimate and/or correct internal states of the load torque observer. The internal states of the load torque observer are in particular the observed angular position, an observed angular acceleration and the load torque. The observer error is multiplied with observer coefficients or observer gains. The observer coefficients are used to adapt the accuracy and the behavior of the load torque observer.

A method according to claim 10 ensures an easy, reliable and accurate estimation of the load behavior. The observer error is multiplied with observer coefficients or observer gains in order to calculate observer signals. These observer signals are used to estimate and/or correct the internal states of the observer. A first observer signal is calculated by multiplying a derivative of the observer error with a first observer coefficient. A second observer signal is calculated by multiplying the observer error with a second observer coefficient. Furthermore, a third observer signal is calculated by multiplying the observer error with a third observer coefficient and by integrating the resulting signal. The load torque depends on the sum of the first observer signal, the second observer signal and the third observer signal.

A method according to claim 11 ensures an easy, reliable and accurate estimation of the load behavior. An observed angular acceleration and in consequence the observed angular position depends on the total inertia of the laundry treatment machine and the load. The total inertia is estimated according to equation (3). The total inertia can be adapted during the operation of the laundry treatment machine, if necessary. For example, the total inertia increases depending on the wetness of the laundry.

A method according to claim 12 ensures an easy, reliable and accurate estimation of the load behavior. Sensorless drive motors are well known and do not comprise an angular position sensor and an angular speed sensor. Hence, the angular position of the drive motor is estimated, for example by means of a position and/or speed estimator or a position and/or speed observer. The load torque observer is preferably provided with an estimated angular position of the drive motor.

A method according to claim 13 ensures an easy, reliable and accurate estimation of the load behavior. The load torque observer is provided with the desired drive torque of the drive motor. An output signal of the speed controller is used to estimate the drive torque. This output signal characterizes the desired electromagnetic drive torque of the drive motor and can be used to estimate the drive torque and/or the load torque which acts on the drum.

Furthermore, it is an object of the present invention to provide a laundry treatment machine which enables to estimate a load behavior in an easy, reliable and accurate manner.

This object is achieved by a laundry treatment machine with the features of claim 14. The advantages of the laundry treatment machine according to the invention correspond to the advantages already described in connection with the method according to the invention.

Further features, advantages and details of the invention will be apparent from the following description of an embodiment which refers to the accompanying drawings.

Fig. 1

shows a schematic view of a laundry treatment machine with a drum, a drive motor and a control unit,

Fig. 2

shows a schematic cross sectional view of the drum with a load located inside the drum,

Fig. 3

shows a block diagram of a controller and a load torque observer implemented in the control unit,

Fig. 4

shows a block diagram of the load torque observer in Fig. 3,

Fig. 5

shows a flow chart of a method to estimate a total inertia of the laundry treatment machine and the load with respect to a rotation of the drum around a rotational axis,

Fig. 6

shows a time diagram of an angular speed and a drive torque of the drive motor during a first operation and a second operation of the laundry treatment machine in order to estimate the total inertia according to the flow chart in Fig. 5,

Fig. 7

shows a first torque signal and a first angular acceleration signal during a first operation and a second torque signal and a second angular acceleration signal during a second operation of the laundry treatment machine as well as a torque difference signal and an acceleration difference signal depending on the angular position of the drum in order to estimate the total inertia, and

Fig. 8

shows an estimated load torque depending on an angular position of the drum.

Fig. 1 shows a laundry treatment machine, namely a washing machine 1 with a cabinet 2 and a washing unit 3. The washing unit 3 comprises a tub 4 and a drum 5. The tub 4 is mounted to the cabinet 2 via dampers 6 and springs 7.

The drum 5 is mounted in a rotatable manner to the tub 4. The drum 5 is connected via a drive shaft 8 with a drive motor 9. The drive motor 9 is mounted at a backside of the tub 4. The drive motor 9 rotates the drum 5 around a horizontal rotational axis 10.

The washing machine 1 comprises several lifters 11 to move the laundry. The lifters 11 are mounted in equal angular distances to an inner side of the drum 5.

Furthermore, the washing machine 1 comprises a control unit 12 to control the operation of the washing machine 1. The drive motor 9 has an angular position Θ, an angular speed ω and an angular acceleration ω̇. Due to the stiff drive shaft 8 the angular position, the angular speed and the angular acceleration of the drum 5 corresponds to the angular position Θ, the angular speed ω and the angular acceleration ω̇. In case of belt driven motor, the pulley ratio will be used to evaluate the angular position, the angular speed and the angular acceleration of the drum starting from the angular position, the angular speed and the angular acceleration of the motor.

The load L, namely the laundry inside the drum 5 produces a load torque T_L. In case that the angular speed of the drum 5 is higher than a satelization speed the load torque T_L can be described by $$T_L=-\mathit{mgr}\sin \left(\mathrm{\theta }+\mathrm{\sigma }\right)$$ wherein

m

denotes the real mass of the load L,

g

denotes the gravitational acceleration,

r

denotes the drum radius,

Θ

denotes the angular position of the drum in relation to a reference position Θ₀, and

σ

denotes the angular relative position of the load L inside the drum, namely an angle between the position of the load L and a drum reference position.

The angular position α of the load L can be described by $$\mathrm{\alpha }=\mathrm{\Theta }+\mathrm{\sigma }$$ wherein

α

denotes the angular position of the load L in relation to the reference position θ₀.

The angular positions σ and α and the mass m are unknown. The gravitational acceleration g and the drum radius r are known. The load torque T_L has a maximum value if α = 90° such that $$T_L=-\mathit{mgr}\cos \left(\alpha \right).$$

The drive motor 9 creates a drive torque T_em which accelerates the drum 5.

The drive torque T_em is superimposed by the load torque T_L.

The control unit 12 comprises a speed controller 13, a torque controller 14, a first coordinate transformation 15, a pulse width modulator 16, a position and speed observer 17, a second coordinate transformation 18 and a load torque observer 19.

The torque controller 14 is part of an inner control loop or a torque control loop to control the drive torque T_em of the drive motor 9. For example, the torque controller 14 is a PI controller. The torque controller 14 is provided with a desired drive torque $T_{\mathit{em}}^{\ast }$ and the drive motor currents which are denoted in common with i_abc. The drive motor currents i_abc are transformed by means of the second coordinate transformation 18 into a dq coordinate system. The corresponding currents are denoted in common with i_dq. The torque controller 14 creates in the dq coordinate system desired voltages which are denoted in common with v*_dq. The voltages v*_aq are transformed by means of the first coordinate transformation 15 into desired voltages in an abc coordinate system which are denoted in common with v_abc. The voltages v_abc are provided to the pulse width modulator 16 which creates via a switch circuit currents i_a, i_b, i_c to operate the drive motor 9 with a torque T_em which corresponds to the desired torque $T_{\mathit{em}}^{\ast }$.

The drive motor 9 is designed sensorless, namely without a speed sensor and a torque sensor. Therefore, the position and speed observer 17 is used to produce an estimated angular position Θ̂ and an estimated angular speed ω̂. The position and speed observer 17 is provided with the voltages v_abc and the currents i_abc. The estimated angular position Θ̂ is provided to the first coordinate transformation 15 and the second coordinate transformation 18.

The speed controller 13 is part of an outer control loop or a speed control loop. The speed controller 13 is provided with the difference of a desired angular speed ω* and the estimated angular speed ω̂. The output signal of the speed controller 13 is the desired drive torque $T_{\mathit{em}}^{\ast }$.

The load torque observer 19 evaluates an estimated load torque T̂_L. The load torque observer 19 is provided with the desired drive torque $T_{\mathit{em}}^{\ast }$ and the estimated angular position Θ̂ as input signals. The load torque observer 19 calculates an observer error e_obs which is the difference of the estimated angular position Θ̂ and an observed angular position Θ_obs.

The load torque observer 19 calculates three observer signals k₁, k₂ and k₃. These observer signals can be described by: $${\mathrm{k}}_1=\mathrm{K}1\cdot \mathrm{s}\cdot e_{\mathit{obs}}$$ $${\mathrm{k}}_2=\mathrm{K}2\cdot e_{\mathit{obs}}$$ $${\mathrm{k}}_3=\mathrm{K}3/\mathrm{s}\cdot e_{\mathit{obs}}$$ wherein

• k₁ denotes a first observer coefficient,
• k₂ denotes a second observer coefficient,
• k₃ denotes a third observer coefficient,
• s denotes a derivator, and
• 1/s denotes an integrator.

The observer coefficients are for example set to $$\mathrm{K}1=64,$$ $$\mathrm{K}2=13,$$ and $$\mathrm{K}3=5.$$

The estimated load torque T_L can be calculated by $${\widehat{T}}_L=-\left(k_1+k_2+k_3\right)$$

The load torque observer 19 calculates an observed angular acceleration ω̇_obs by $${\dot{\mathrm{\omega }}}_{\mathit{obs}}=\frac{1}{{\widehat{J}}_t}\cdot \left(T_{\mathit{em}}^{*}-{\widehat{T}}_L\right)$$ wherein
Ĵ_t is the total inertia of those parts of the washing machine 1 which rotate around the rotational axis 10, in particular of the drum 5 with the balancers 11, of the drive shaft 8, of the drive motor 9, and of the load L. The total inertia can be described by$${\widehat{J}}_t={\widehat{J}}_L+{\widehat{J}}_m$$ wherein
Ĵ_L denotes the load inertia and J_m denotes the inertia of the washing machine 1. The inertia of the washing machine 1 is known from construction data.

The load torque observer 19 calculates an observed angular speed ω_obs by integrating the observed angular acceleration ω̇_obs. Furthermore, the load torque observer 19 calculates the observed angular position Θ_obs by integrating the observed angular speed ω_obs.

In the following the estimation of the total inertia Ĵ_t is described in detail:
In step S₁ the speed controller 13 is parametrized with first controller parameters P₁. For example, the speed controller 13 is a PI controller.

In a second step S₂ the drum 5 is accelerated by means of the drive motor 9 as example from 0 rpm to 100 rpm.

Afterwards, in a third step S₃ the drum 5 is rotated with an essentially constant drum speed ω. During the third step S₃ the control unit 12 transforms the desired drive torque $T_{\mathit{em}}^{*}$ and the estimated angular speed ω̂ into the frequency domain by calculating a Fourier Transformation. The first harmonic of the desired drive torque $T_{\mathit{em}}^{*}$ is stored in the control unit 12 and is denoted $T_{\mathit{em}}^{\ast 1}$. Furthermore, the first harmonic information, for example the frequency, the amplitude and the phase, of the estimated angular speed ω̂ are used to get an estimated angular acceleration which is denoted $\widehat{{\dot{\omega }}^1}$. The estimated angular acceleration $\widehat{{\dot{\omega }}^1}$ is stored in the control unit 12.

Afterwards, in a step S₄ the speed controller 13 is parametrized with second controller parameters P₂.

Afterwards, in a fifth step S₅ the drum 5 is rotated with an essentially constant drum speed ω. During the step S₅ the control unit 12 transforms the desired drive torque $T_{\mathit{em}}^{*}$ and the estimated angular speed ω̂ into the frequency domain by calculating a Fourier Transformation. The first harmonic of the desired drive torque $T_{\mathit{em}}^{*}$ is stored in the control unit 12 and is denoted $T_{\mathit{em}}^{\ast 2}$. Furthermore, the first harmonic information, for example the frequency, the amplitude and the phase, of the estimated angular speed ω̂ are used to get an estimated angular acceleration which is denoted $\widehat{{\dot{\omega }}^2}$. The estimated angular acceleration $\widehat{{\dot{\omega }}^2}$ is stored in the control unit 12.

In a subsequent sixth step S6 the total inertia can be calculated by $${\widehat{J}}_t=\frac{T_{\mathit{em}}^{\ast 1}-T_{\mathit{em}}^{\ast 2}}{\widehat{{\dot{\omega }}^1}-\widehat{{\dot{\omega }}^2}}$$

The estimated total inertia Ĵ_t is used to parametrize the load torque observer 19. Equation (15) is illustrated in fig. 7.

After parameterization the load torque observer 19 can be used in a seventh step to observe and estimate the load torque T̂_L. Furthermore, the load inertia can be calculated by $${\widehat{J}}_L={\widehat{J}}_t-J_m$$ and the estimated mass m̂ of the load or the unbalance mass can be calculated by $$\widehat{m}=\frac{\max \left({\widehat{T}}_L\right)}{\mathit{gr}}$$

The angular position Θ̂ of the load L is already known. Fig. 8 illustrates the estimated load torque T̂_L.

The load inertia Ĵ_L, the load torque T̂_L, the mass m̂ and the angular load position Θ̂ characterize the behavior of the load L and can be used for several purposes, for example to adapt the maximum spinning speed, to compensate the load L by filling the balancers 11 with water, to estimate the dry load at the beginning of the washing cycle and to set properly the required amount of water and/or detergent, to estimate the wet load at the beginning of the spinning cycle and to estimate the remaining moisture retention during a drying process.