GB2205185A - Motor shaft position sensor - Google Patents

Abstract

To sense the angular setting of the shaft of a commutator-type motor (1), a toroidal transformer (5) is provided, through which pass the motor's supply leads. Thus as the motor moves it generates a pulse train the number and sense of the pulse of which indicate how far the shaft has turned. These pass to an up/down counter via an operational amplifier (6). A number of such sensors are used with a car seat adjuster, such that each motor of the adjuster is driven under comparator control to the desired setting. The mirrors of the car may be additionally controlled. <IMAGE>

Description

MOTOR SHAFT POSITION SENSOR This invention relates to an arrangement for sensing the angular position of a shaft, such as the shaft of an electrical motor.

According to the invention, there is provided an arrangement for sensing the angular position of the shaft of an electrical motor of the commutator type, which includes a toroidal transformer through which at least one current supply lead for the motor is threaded, so that the current supply lead forms a primary winding for the transformer, a secondary winding on the transformer so that current flowing to the motor produces an output from the secondary winding, and counting means fed from the secondary winding such that when the shaft moves to a new setting the secondary winding produces a pulsed output, the number of pulses in a said output indicating the position of the shaft, which pulses set the counting means to a sate appropriate to that of the shaft.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 shows a known arrangement for feeding an electrical motor which is part of an arrangement for adjusting a seat in a car.

Figs. 2, 3, 4 and 5 show arrangements according to the invention for sensing the angular position of an electrical motor shaft.

Fig. 6 shows a system for controlling the position of a car seat using sensors such as those of Figs. 2 to 5.

In the known arrangement of Fig. 1, the motor 1 is connected to the supply via a plug/socket combination 2 and a switch 3, which is a double pole change-over switch with a central off position. With the usual DC car supply thus enables the motor to be driven in either direction.

Fig. 2 shows the use with the circuit of Fig. 1 of a sensor embodying the invention for determining the angular setting of the motor shaft. The sensor includes a toroidai core 5, of ferrite or ferro-magnetic strip, threaded by the power leads at a point between the plug/socket combination and the motor 1. This core has a secondary winding feeding an operational amplifier 6, whose output taken via two buffers is a pulse train the number of pulses of which received when the motor drives defines the position of the shaft.

With a DC motor the drive current is interrupted by a commutator which rotates and changes the coil of the motor in which current flows. By monitoring this current interrupt, a series of pulses dependent on the number of commutator segments is obtained which can be enhanced by the operational amplifier and counted. Counting up or down depends on the direction in which the motor is driven. An up/down counter chip (not shown), which is commercially available, counts the number of pulses and gives the rotational position.

If the motor used is an AC commutator type one, the monitoring gives a series of pulses superimposed on a 50Hz signal. The 50 Hz signal is removed in known manner to leave a pulse train proportional to the angular position of the motor shaft.

The transformer on the core 5 has a secondary winding of about 300 turns, the supply leads forming a low-turn primary. The core itself is a toroidal ferrite or a strip iron core bent to form a ring. An output of several millivolts is obtained across the secondary when open-circuited if the supply current is about 2 amps.

As a result of the amplification by the amplifier 6 the output is substantially square wave, which is improved by a capacitor across the amplifier output and the two buffer inverters. As the pulse frequency is relatively low, the capacitor damps out spurious signals due to noise in the motor and to noise from associated switches and equipment.

The connection shown to a manual switch enables a user to switch the motor on to drive either way, the choice depending on the initial angular setting of the motor shaft.

If a memory system is added, preselected counts can be recalled using a comparator whose output can be arranged to interrupt the motor supply to stop the motor when its shaft has been driven to a desired setting, or the supply polarity changed to control the direction of movement.

Fig. 3 shows the arrangement to be used when a sensor such as that of Fig. 2 is used as a "retrofit" connection to an existing motor installation. The supply connection includes two contacts of a relay 7 which is operated from the control module and whose contacts switch so that the motor is driven from the module output. This ensures that when the manual switch is operatd at the same time as the electric module the supply is not shorted.

Fig. 4 shows a system which is in general similar to that of Fig. 2, but with an extra output 10 for use to indicate whether the manual switch is being used or not.

Fig. 5 is a version of the circuit of Fig. 2, in which the switch is a three pole double throw switch, in which one setting gives a module output with a 12 volt supply.

Fig. 6 shows how the arrangements described above can be used in a system for adjusting the position in three directions of a car seat. This has three motors such as 21 each with its own sensor 22 and up/down counter, coupled via a multiplexer 23 to a comparator 24.

There is also a memory 25 in which th driver has stored the settings he likes for the car seat. This has two input buttons, one, DRIVER SELECT, for putting in the settings, and the other, SET, which the driver operates when he enters the car. This, as will be seen below, causes the seat to be set in accordance with the settings in the memory.

When the seat is being set, the settings are compared successively in a comparator 26 with the output of the sensors such as 23, and each comparison provides an output if the s'etting is not correct. These error outputs are applied via another multiplexer 27 to the output drive circuits such as 28 for the motors. When this occurs each motor drives to its current setting, and when it reaches that, the comparator output disappears to stop the drive.

Additional drive movements can be provided if desired for setting the car's mirrors.

Although not shown, manual over-rule is provided for use if the control module fails.

The connection shown from the ignition switch supply ensures that on switching off some movements revert to zero so that the driver can get out of the seat. In addition, on switching on the ignition, the seat moves to the last driver's preferred position.

Claims (5)

1. An arrangement for sensing the angular position of the shaft of an electrical motor of the commutator type, which includes a toroidal transformer through which at leas one current supply lead for the motor is threaded, so that the current supply lead forms a primary winding for the transformer, a secondary winding on the transformer so that current flowing to the motor produces an output from the secondary winding, and counting means fed from the secondary winding such that when the shaft moves to a new setting the secondary winding produces a pulsed output, the number of pulses in a said output indicating the position of the shaft, which pulses set the counting means to a state appropriate to that of the shaft.

2. An arrangement as claimed in claim 1, and in which the magnetic circuit of the transformer is a ferrite toroid or a strip of iron bent to form a ring.

3. kn arrangement for adjusting the position of a device, in which for each movement needed there is provided an electrical motor of the commutator type, in which each motor has a sensing arrangement as claimed in claim 1 or 2, whose output is applied to comparison means, in which inputs appropriate to the desired settings of the or each said motor are also applied to the comparator so that the latter produces an output for each motor not correctly placed, and in which said outputs are applied to the motor or the appropriate motor to adjust the position thereof.

4. An arrangement for sensing the angular setting of a motor shaft, substantially as described with reference to Fig. 2,3, 4 or 5 of the accompanying drawings.

5. An arrangement for adjusting the position of a car seat, substantially as described with reference to Fig. 6 of the accompanying drawings.