EP0523794B1 - Iron with motion detector - Google Patents

Description

The invention relates to an iron comprising a heating element, means for controlling the heating of the heating element, and a motion detector.

An iron can give rise to certain problems when after being switched on it is left stationary on a cloth. Depending on the temperatures reached, the fabric may be damaged. For this, it is useful to provide the iron with a safety device which stops the iron when not in use. This is usually done by determining the movement of the iron using a motion detector.

Such a detector is for example described in patent EP 0227150. This detector comprises a magnet mounted at the end of a pendulum which oscillates with the movement imparted to the iron by the user. An electrical signal generated by this movement makes it possible to detect when the iron is in use and consequently when it is not in use. However, such a device proves to be expensive to produce industrially. In addition, the balance moves substantially in an oscillation plane which is parallel to the axis of movement of the iron which is oriented in the direction of the tip of the soleplate of the iron. A movement perpendicular to this oscillation plane is then not detected. Having moving parts (see DE-A-3 444 348) also constitutes a handicap.

The object of the invention is to propose a motion detector for an iron which is inexpensive to manufacture industrially, which is devoid of moving parts and therefore of simple construction.

• des moyens pour capter des charges électrostatiques créées sur un tissu par glissement du fer à repasser,
• des moyens pour détecter un mouvement du fer à repasser en mesurant un rythme d'un signal électrique issu de variations des charges électrostatiques.

This object is achieved using a motion detector formed by an electrostatic detector which includes:

• means for picking up electrostatic charges created on a fabric by sliding the iron,
• means for detecting a movement of the iron by measuring a rhythm of an electric signal resulting from variations in the electrostatic charges.

According to the invention, the quantity of electrostatic charges generated on the surface of the fabric by the passage of iron is measured. to iron on the fabric. It is then possible to determine variations in the quantity of electrostatic charges, variations which determine the movement.

The sensitivity of the detector can be advantageously reinforced by placing near the detector a plate of insulating material which, by friction with the fabric, generates electrostatic charges on the surface of the fabric.

The iron can thus be provided with a member, consisting of an electrically insulating material, which is arranged with the iron to generate by friction electrostatic charges when the iron slides on the fabric.

The insulating material can be, for example, Teflon *, glass, enamel, Kapton *.
*trademark

Such an electrostatic detector is mainly intended to be used for ironing dry fabrics. Indeed, when the fabric is wet, the ability of a fabric to store electrostatic charges decreases. It follows that the electrostatic detector sees its effectiveness decrease when the humidity of the fabric is higher and higher.

• des moyens pour mesurer une résistivité du tissu,
• des moyens pour détecter un mouvement du fer à repasser en mesurant un rythme d'un autre signal électrique issu de variations de résistivité dues au glissement du fer à repasser sur le tissu.

To continue detecting the movement of the iron even with damp fabrics, according to the invention, a humidity detector which delivers an electrical signal when the fabric is wet is added to the electrostatic detector, this humidity detector comprises:

• means for measuring a resistivity of the fabric,
• means for detecting a movement of the iron by measuring a rhythm of another electrical signal resulting from variations in resistivity due to the sliding of the iron on the fabric.

Indeed, the passage of the iron over areas which generally do not have the same humidity allows the humidity detector to deliver an electrical signal which varies according to the position of the iron. These variations are used to detect the movement of the iron operating on damp fabrics.

The means for measuring the resistivity comprise at least one conductive terminal which is flush with the soleplate of the iron for be brought into contact with the fabric.

The humidity detector can further determine an average degree of moisture in the fabric using means for measuring an average amplitude of said other electrical signal.

The invention will be better understood using the following figures given by way of non-limiting examples which represent:

Figure 1: a side view of an example of an iron with an electrostatic detector.

Figure 2: two diagrams A, B of an electrostatic detector implementing electrostatic charge measurements.

Figure 3: a schematic view of the underside of an iron with a humidity detector and an electrostatic detector.

Figure 4: a diagram of an electrical resistivity measurement circuit.

Figure 5: curves representing the variations DR of resistance and the variations DQ of electrostatic charges during a drying operation.

Figure 6: an example of a curve of variations of an output signal I (d) as a function of displacement.

Figure 7: an example of a rhythm measurement circuit.

Figure 8: an example of a rhythm and humidity measurement circuit.

The electrostatic detector will be arranged with the iron so that it is placed opposite fabric when the iron slides on the fabric. The diagram in FIG. 1 represents an iron 30 provided with an electrostatic detector 35 placed at the rear of the sole 31 of the iron.

The electrostatic detector is represented on figure 2. The figure 2-A represents a metal electrode 40 electrically connected to a circuit 41 of electrostatic voltmeter with high impedance. The electrode 40, electrically isolated by an insulating column 46, is placed in a shield 42 so that the measurement is not disturbed. A coaxial connection 43 can be used between the electrode 40 and the circuit 41 of the voltmeter. The electrode 40 is arranged with an iron to be located a short distance from the fabric 45. Thus the quantity of electrostatic charges generated on the surface of the fabric by the moving soleplate of the iron can be measured, by capacitive effect, using the electrode 40. Between the electrode 40 and the fabric 45 appears a capacity C _o . Between the electrode 40 and the shielding 42 there appears a capacitor C₁.

The electrical signal appears in the form of a signal whose amplitude varies with the movement of the iron on the fabric.

• soit automatiquement,
• soit en plaçant à demeure une résistance de fuite aux bornes de la capacité C₁,
• soit en effectuant cycliquement un court-circuit de l'électrode 40.

To avoid electrostatic charges accumulating to the point of saturating the input stage of the electrostatic voltmeter circuit 41, which would prevent the measurement of signal fluctuations, it is possible to carry out resets. For this, a predetermined threshold of electrostatic charges is not to be set. When this threshold is reached, the electrode 40 can be reset to zero:

• either automatically,
• either by permanently placing a leakage resistance across the terminals of the capacitor C₁,
• either by cyclically shorting the electrode 40.

The capacitive bridge is represented on the figure 2-B. By measuring the electrostatic potential V₁ at the limits of the capacitance C₁ we can deduce the quantity of charges on the fabric. Experimentally, with values C _o and C₁ fixed by construction, the measurement of V₁ makes it possible to determine the electrostatic character of the fabric. As an indication, comparative values (given in arbitrary units) are provided for several types of tissue. Cotton 1 to 5 Viscose 1 to 5 Acetate 15 to 20 Polyester 18 to 24 Acrylic 15 to 20 Nylon 14 to 18 Oldest boy 18 to 24 Silk 14 to 20

It is observed that most of the fabrics which require low ironing temperatures have the character highest electrostatic.

It is possible to increase the quantity of electrostatic charges generated by providing the iron with an organ made of an insulating material which is arranged with the iron to generate by friction electrostatic charges when the iron slides on the fabric. It can be formed for example of a plate 64 (FIG. 3) located near the electrostatic detector 35. The plate 64 can partially or totally surround the electrostatic detector with an L or circular shape. The plate can for example be made of Teflon *, glass, enamel, Kapton *.

When the moisture content of the fabric is too high, the generation of electrostatic charges is weakened and can even be canceled. A measurement of the rate of variation of the electrostatic charges is then obtained by using a humidity detector which measures the electrical resistance of the fabric between two contact terminals. An advantageous embodiment is thus obtained by operating the two detectors in a complementary manner. FIG. 3 represents a schematic view from below of an iron 30 provided with a humidity detector 60 and an electrostatic detector 35. The humidity detector 60 comprises two terminals 62 _a , 62 _b which preferably have a rounded shape, hemispherical for example, to be able to slide easily on the fabric. Terminals from 5 mm to 10 mm in diameter, for example made of stainless steel, are suitable. These terminals can be mounted on an elastic support 64 to apply well to the fabric without leaving any traces. These terminals are combined with the measurement means which determine the rhythm of the variations in the electrical resistance of the fabric. If said value of electrical resistance is low, the fabric is damp. If said value is high, the fabric is dry. The terminals are placed in housings 63 _a , 63 _b formed in the support 64.

When it is desired to increase the quantity of electrostatic charges generated, the member to be arranged can be constituted by this support 64 by making it from an electrically insulating material, for example Teflon *, glass, an enamelled sheet, Kapton * . The material must have sufficient temperature resistance to be brought into contact without deteriorating with more or less hot fabrics. So that the electrostatic detector 35 can operate in several directions of sliding of the iron, it is possible that the support 64 partially or completely surrounds the measurement electrode 40. For example, an L or circular shape may be suitable.
*trademark

FIG. 4 represents a diagram of an electrical circuit for measuring the resistivity. The terminals 62 _a , 62 _b , which are in contact with the fabric 45, are connected to an electrical supply 90 and to a circuit 89 for measuring the electric current I passing through the circuit.

FIG. 5 represents curves of the variations DR of the resistance and of the variations DQ of electrostatic charges during a dehumidification operation for an iron as shown in FIG. 3. By placing and then sliding the iron in the direction of its front point, with a slightly heated sole 31, the humidity detector 60 encounters increasingly dry parts of fabric (over a length of iron sole). We then observe curves A and C for cotton and curves B and D for acrylic depending on the degree of drying. Curves C and D relate to variations DQ of electrostatic charges. Curves A and B relate to the variations DR of electrical resistance. They are provided in arbitrary units. When the resistance becomes high, the amount of electrostatic charges increases in relation to the nature of the fabric. In reality, the tissues never have a constant humidity which causes fluctuations in the signal depending on the movement of the iron.

FIG. 6 represents a curve of variation of an output signal I (d) as a function of the displacement d of the iron. It is representative of both a signal from the electrostatic detector and a signal from the humidity detector. The signal is formed by a sequence of alternations having variable amplitudes. To detect movement, the number of signal ascents and / or descents is calculated for a predetermined period. These signal alternations are caused by the movement of the iron.

FIG. 7 represents an example of circuit 89 allowing to determine the number of alternations. It comprises a capacitor C₃ and a resistor R₃ connected to an input of an amplifier 92 with high input impedance. This circuit derives the signal I and supplies pulses at each rising and falling edge of the signal. These pulses are then counted in a counter 93 which delivers on an output 94 a signal S when a zero or very limited number of pulses (for example 1 to 3) has appeared during the predetermined duration. This signal S is then used to act on the means 96 for controlling the iron in order to stop the heating of the heating element 97.

The other input of amplifier 92 can be grounded. In this case, the soleplate of the iron can replace the terminal 62 _b . The humidity detector then comprises a terminal 62 _a and the sole 31 as a second terminal.

It is also possible to add to circuit 89 above another circuit 99 which determines the average amplitude of the signal I (d). (Figure 8). This average value is then representative of the degree of humidity of the fabric. The other circuit 99 comprises a resistor R₁ connected by one end to the input terminal 88 for supplying the current I, the other end of this resistor R₁ being connected to an amplifier 91 with high input impedance. Between the input and the output of this amplifier 91, an arrangement formed of a capacitor C₂ and a resistor R₂ has been arranged in parallel. On exit 95 a signal representing the average humidity level of the fabric thus appears. This signal can then be used to act on the means 96 for controlling the iron to, for example, increase the electrical power dissipated in the heating element 97 to accelerate the speed of dehumidification of the fabric.

Claims (8)

1. An iron comprising a heating element (97), heating-control means (96) for the heating element, and a motion detector, characterised in that the motion detector is an electrostatic detector (35) comprising:

   - means (40, 42, 43, 46) for picking up electrostatic charges produced by a movement of the iron on a fabric,

   - means (41, 89) for detecting a movement of the iron by measuring a rhythm of an electric signal resulting from variations of the electrostatic charges.
2. An iron as claimed in Claim 1, characterised in that the iron comprises an element (64) made of an electrically insulating material and arranged on the iron to generate electrostatic charges by frictional contact as the iron slides on the fabric.
3. An iron as claimed in Claim 2, characterised in that the insulating material has been selected from the following list: Teflon®, glass, enamel, Kapton®.
4. An iron as claimed in Claim 2 or 3, characterised in that the element (64) partly or wholly surrounds the electrostatic detector.
5. An iron as claimed in any one of the Claims 1 to 4, characterised in that it further comprises a humidity detector (60) comprising:

   - means (62a, 62b) for measuring a resistivity of the fabric,

   - means (89, 90) for detecting a movement of the iron by measuring a rhythm of another electric signal resulting from resistivity variations caused by the movement of the iron on the fabric.
6. An iron as claimed in Claim 5, characterised in that the means for measuring the resistivity comprise at least one conductive electrode (62a), (62b) which is flush with the soleplate of the iron in order to be brought into contact with the fabric.
7. An iron as claimed in any one of the Claims 1 to 6, characterised in that the means (89) for detecting the movement comprise:

   - a differentiation circuit for the electric signal I,

   - a counter (93) which, during a predetermined time interval, measures a number of pulses appearing on the output of the differentiation circuit and characterising either said signal or the other signal, and which stops the control means (96) of the iron when said number of halfwaves is smaller than a very small predetermined number.
8. An iron as claimed in any one of the Claims 1 to 7, characterised in that the humidity detector in addition detects an average degree of humidity of the fabric with the aid of means (99) which measure an average amplitude of said other electric signal.

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