Manual work on fine structures is made much more difficult by the contraction of antagonistic muscles occurring involuntarily, and in largely rhythmic succession, and referred to as tremor. This is noticeable particularly in microsurgery when suturing fine nerves or vessels, prolongs the duration of the operation and reduces the quality of the result.
However, in order to be able to perform filigree work, use is made, for example, of supports for the hands, or micromanipulators, which convert relatively rough movements into fine deflections.
The object of the invention is to make available a handheld instrument for the manual manipulation of fine structures, in which undesired movements, for example tremor, have no effect, or at least less effect, on the manipulation.
The invention is based on the concept of evaluating the undesired movements of handheld instruments and of deflecting, by means of actuators, the working tip of the instrument (in surgical applications this would be, for example, a needle holder) in order to provide compensation, so that the hand tremor cannot be observed at the tip.
Since the physiological tremor takes place in a range of between about 5 and 15 strokes/second, it can be differentiated from slower voluntary movements, for example by frequency-selective filtering.
According to the invention, one or more devices can be provided for detecting movements on the part of the user, in particular for detecting movements of the instrument caused by the user, for example active or passive measurement transducers, by means of which undesired movements on the part of the user, or movements of the instrument caused by the user, can be detected. The output signals from these devices are used, if appropriate after suitable evaluation and processing, to trigger actuators of the instrument for the purpose of compensating for the undesired movements.
To detect the movement of the instrument, a number of possibilities can be selected in principle, and these can be combined with one another:
1. Acceleration and angular velocity sensors are arranged on one or more sections of the instrument, which sensors supply a mechanical or electrical signal correlated with the movement of the instrument.
The function of the sensors can be based on purely mechanical, electromagnetic, capacitive, piezoelectric or piezoresistive principles. The sensors have to detect the movement with sufficient sensitivity and accuracy. In this connection, it is conceivable to use sensors which have their maximum sensitivity in the frequency range in which the undesired movements take place and thereby deliver an output signal correlated with the tremor. The sensors can be arranged in such a way that they can detect both translational movements and rotational movements of the instrument.
2. According to the invention, one or more devices can be provided for repetitive or continuous detection of the position of certain sections of the instrument in one, two or three dimensions, in particular of a handheld section and/or a section of the instrument which is movable in relation to the handheld section. By repetitive or continuous detection of the position and orientation of certain sections of the instrument, their movement can be followed. The detection can take place in one, two or three dimensions. This can be done by wireless means via a transmitter/receiver system on the instrument and at reference points which are located at fixed positions in space or on the area being worked on.
It is also possible, particularly for use in microsurgery, to follow the movement of the section of the instrument shown in the operating microscope. The microscope image is delivered to an image-recording unit which determines the positions, in the image, of certain features or optical markings on the instrument and calculates the movement on the basis of the consecutive position data. To do this, tracking procedures can also be used.
If, in addition, the movement of the tissue being worked on is also detected, this movement likewise being shown under the operating microscope, the movement of this tissue caused, for example, by the tremor on the part of the patient can be included in the compensation process.
3. With surface electrodes arranged on the skin of the person operating the instrument, the action potentials of the underlying muscle can be recorded (so-called electromyography). If a control system recognizes the movement which the corresponding muscle causes on innervation—for example through the ability to adapt—it is possible, by combining the electrode signals, to draw conclusions regarding the deflection the instrument is expected to make. In this method, the actual use of the instrument would be preceded by a “learning phase” in which the signal processing unit correlates the electromyographic signals with results of other movement-recording methods, and thus adapts to individual features of the operator and to the positioning of the reference electrodes.
If the movement detection has not already supplied a signal which corresponds to the movement attributed to the tremor and is thus suitable for directly triggering the actuators, the signal is processed.
In general, it will first be necessary to amplify the sensor signal. This is followed by analysis which differentiates between intentional and unintentional movements on the basis of criteria such as frequency, amplitude, speed and direction. The criteria can be predefined, adjusted, or adapted automatically. On the basis of the data, a signal is obtained with which the actuators are triggered so that said actuators execute, at the working tip of the instrument, relative movements for compensating for the undesired deflections of the handheld section.
The actuators can be both purely mechanical arrangements and also electrical controls which are based, for example, on electromagnetic, capacitive or piezoelectric principles. The actuators execute relative movements between the handheld section and the movable section of the instrument. They must be able to execute the desired movements with sufficient speed, power and precision. The actuators can be arranged in such a way that they can effect both translational movements and rotational movements. For certain requirements, it may be desirable that the actuators can also temporarily bring about a rigid connection between the handheld section and the movable section. The working tip of the instrument can be mounted in a fixed manner or can be designed to be exchangeable. Actions, such as the opening and closing of grippers or forceps, which must necessarily be done from the handheld section of the instrument, can be triggered via a flexible power transmission, for example a flexible push rod, which does not impede the actuators, or via electrically operated adjustment members on the moved section.
It may be useful, especially for use in microsurgery, to trigger the actuators already present in the instrument by means of a push button in such a way that they cause the working tip of the instrument to oscillate at frequencies in the sonic or ultrasonic range, and, for example, when used as a needle holder, facilitate the penetration of the suture needle into tissue, as a result of the rapid micro-movements.