The Electric Wheelchair on Shabbat
|Rav Yair Meir|
A. The Problem
1. The Grama Switch
2. Spring Return
3. Modulating the Current
4. Minimum Current
5. Changing the Duty Cycle
A. The Problem
In recent years, the use of wheelchairs with electric motors has become common. These wheelchairs use a storage battery similar to that found in automobiles, which is charged by connecting it to ordinary house current for several hours when the wheelchair is not in use. The chair is operated by means of a joystick, which controls both steering and acceleration.
The wheelchair permits a high degree of mobility for wheelchair-bound invalids who cannot operate a regular wheelchair, both in the house and outside. The invalid is able to feel independent and self-sufficient, which is extremely important for his self-esteem.
Two outstanding Torah authorities in
B. The Prohibitions Involved
Use of an electric motor on Shabbat, which does not result in the creation of light or any other Shabbat creation, is the subject of a continuing discussion among scholars. In our case, where the source of the current is a battery, the problem of power generated on Shabbat does not exist. The battery is not a
generator, and only releases power stored before Shabbat when it was charged. There are three possible categories of Shabbat prohibition that apply:
A. Creating current - the Beit Yitzchak
B. Construction - the Chazon Ish
C. Completing a utensil - the Tzitz Eliezer
A. Creating Current - The Beit Yitzchak (YD, addenda n.31) maintains that completing a circuit is subject to the prohibition of creating current, which is derived by analogy from the Talmudic category of creating scent (Beitza 22a).
Rabba said: (Placing incense) using potsherds is forbidden as well, because it creates a scent (Rashi - "which enters the potsherd, which previously did not smell. It is prohibited rabbinically because creating something new is similar to doing a new melacha (forbidden category of labor on Shabbat). Rabba and R. Yosef both said: Overturning a cup (of perfume) on fabrics is forbidden on a festival. Why? Because it creates a scent. Why is this different from (the permitted activity of) crushing a herb in order to smell it? In that case the scent exists already and he is only adding to it; here he is creating a scent.
According to Rashi, creating a scent is a rabbinic prohibition based on the Torah concept of melacha: however, if the scent is preexistent, increasing its intensity is not forbidden. For a discussion of the various opinions concerning the prohibition of scent-creation as well as the analogy with creation of electric current, see Prof. Z. Lev, "Electricity and Shabbat", Crossroads v.II, p.7ff.
Rav Shlomo Zalman Auerbach (Kovetz Maamarim BeInyanei Chashmat, p.54), while questioning the possibility of extending the prohibition of creating beyond those cases explicitly mentioned in the Talmud, nevertheless concludes that the authority of the Beit Yitzchak is sufficient reason to accept the practical ramifications of his opinion.
B. Construction - The Chazon Ish (OH 50,9) maintains that completing an electric circuit falls under the category of construction (boneh).
This is a case of completing a utensil, since he is causing it to fulfill its quality
of conduction in a permanent manner. It seems probable that this falls under the category of construction, the same as one who makes a utensil. This case is even more (like construction than making a utensil), as the wires are connected to the house, so that it is similar to
a case of attached construction.... Completing a circuit, whereby current enters the wires, is always considered a case of a "firm" connection... (as) the granting of form to a body, through which it becomes usable, is definitely considered construction. (This is true) even if the use is for a specific time, ater which it ceases, as the cessation is a new state, and the original form is not by itself separable from the body. Since turning it on is construction. breaking it is destruction.
A detailed and exhaustive discussion of this opinion is found in the article of Rav S.Z. Auerbach, "Birurim BeInyan Melechet Boneh Ve-Soter" (Kovetz Maamarim Beinyanei Chashmal, p.59). The main objections to this opinion
A. Operating a motor through release of some form of potential energy, such as releasing the spring of a wind-up toy (cf. Shemirat Shabbat KeHilchatta 15,10), or using pneumatic power to open a door, is not prohibited on Shabbat. This is supported by the discussion of the Talmud (Shab. 18) concerning the use of a water mill on Shabbat, in regard to the prohibition of grinding. No one ever questioned the operation of the mill itself, which is done by rechanneling the water over the wheel of the mill.
B. A straight forward reading of the Talmud indicates that a "firm" connection is one that requires a degree of strength as well as the application of a measure of skill. This is not applicable to closing an electric switch, which requires no skill and is performed easily. The distinction proffered by the Chazon Ish between the connection of two bodies, where a "firm" connection is required, and the combination of "form and body", which is automatically considered "firm", finds no support in traditional sources.
Rav Auerbach himself accepts the conclusions of the Chazon Ish for all practical purposes, even while questioning their logical basis.
C. Completing a utensil - This possibility is advanced by several authorities, most extensively by the Tzitz Eliezer (6,6: 3,16). According to many commentators, who maintain that the category of construction does not apply to utensils not attached to the ground, completing or fixing a utensil falls under the category of makeh bepatish. The Rambam (Hilchot Shabbat 23,4) states: "Anything which is the completion of a melacha is prohibited because of makeh bepatish. Therefore... repairing (completing) a utensil in any way is prohibited."
The basic problem with the application of this category to closing a circuit is that it would appear that completing a utensil is appropriate only where an unfinished utensil is actually completed, but not to a procedure which is part of the normal operation of the finished utensil, where the nature of the utensil requires that one be able to start and stop a given operation. The switch, in such a case, is a functioning part of the completed utensil, and not the last step in its completion. This distinction lies at the basis of the difference between winding up a child's toy, which should be permitted, and winding a watch, which many authorities prohibit (Shemirat Shabbat Kehilchatta, citing Rav S.Z. Auerbach). A watch, unwound, is useless: if we could, we would invent a watch that would never cease. Hence, it may be considered to be "broken" when unwound, and winding it is completing, i.e., fixing it. Use of an electric device, such as the wheelchair, necessitates stopping as much as operating, so that starting it is not completing it, but part of its operation.
One can find support for this conclusion in the explanation of Rashi to the "plasterer's rod" (Shab. 47a). The Talmud states that attaching the parts of this device is permitted by the Torah but prohibited rabbinically. Rashi explains:
Plasterers who coat and whiten the house with plaster have a pole composed of: parts to which a cloth is attached at the end.... At the bottom (of the wall), he must use a short pole; as he rises, he keeps adding poles and lengthens it. It is not a Torah prohibition, since this is not its completion, as he will have to recurrently disassemble it.
It would appear that the plasterer's pole is assembled "firmly", as otherwise there would be no need for an additional explanation Why it is not a Torah prohibition. It is conceivable that if the connection were "loose", and the process one of use rather than completion, as explained by Rashi, there would be no disagreement concerning its permissibility. This is surely true according to R. Shimon b. Gamliel, who maintains that it is permitted to assemble any utensil in a "loose" manner
Reading the relevant responsa on the subject of electricity on Shabbat, one gets the distinct impression that the Torah scholars felt that use of electricity must be prohibited on Shabbat, even though it is not completely clear why, as otherwise the distinctiveness of Shabbat as a day of rest would be threatened. Each one therefore offered a different explanation, although objections could be raised against each one in turn. This brings to mind a statement of the Yerushalmi (Shab. 7,2): "That for which a classification was found, was classified accordingly: that for which no classification was found, was treated as makeh bepacish." The Pnei Moshe explains that any creative activity for which no other Shabbat category seemed appropriate was included under the heading of makeh bepacish, which includes the completion of any creative activity.
In light of this statement and the various considerations raised above, it would appear that the most appropriate category for the use of electricity is completing a utensil, which is included under makeh bepatish. Nonetheless, as was mentioned above, Once two great scholars have ruled to include it in the Torah category of construction and the rabbinic prohibition of creation, we cannot permit use of any device in contradiction to those opinions.
C. The Halachic Status of the Invalid
There is very little halachic literature concerning wheelchair-bound invalids. Substantial discussion refers to critical illness, where even Torah prohibitions are suspended, as well as noncritical illness, where, under certain conditions, rabbinic prohibitions may be set aside. One of the definitions of the latter condition is "one who is bedridden, and also one who suffers pains to the extent that his entire constitution is weakened even if he is not confined to bed." In such a case, rabbinic prohibitions may be set aside in order to relieve his suffering, as "rabbinic prohibitions were not promulgated in cases of illness and suffering." Rav Shlomo Zalman Auerbach has advanced the opinion that if all Torah prohibitions can be eliminated from the operation of the electric wheelchair, its use on Shabbat by an invalid would be permitted.
Another basis for permitting use of the electric wheelchair on Shabbat, provided that all Torah prohibitions are eliminated, can be found in the Tzitz Eliezer (6,6,3).
The responsum of the Tzitz Eliezer deals with wearing a hearing aid and the
prohibition of muktza. He writes:
The Shulchan Arulch (OH 312,1) rules: It is permitted to transport stones (which are muktza) in order to wipe oneself, because of (the principle of) human dignity (kvod habriot). It is permitted even to carry them to the roof, which constitutes excessive work. The Lvush (ibid.,1) explains the reason: "As you know, human dignity is so important that it suspends even a negative commandment of the Torah, namely the injunction 'You may not ignore'.... Here too, transporting (muktza) is a rabbinic prohibition... and is suspended when in conflict with human dignity. Therefore, the Sages permitted transporting stones on Shabbat in order to wipe with them, as this serves the purpose of human dignity." The source and explanation of this law is found in the Talmud (Shab. 81), and Rashi (ad.1oc.): cf. Tiferet Yisrael, Kalkelet HaShabbat, Muktza. We see from the above that the prohibition of muktza is suspended when in conflict with the principle of human dignity, and a man need not be disgraced in his own eyes and in the eyes of others in any manner whatsoever by the necessity to refrain from transporting some object. Accordingly, it would appear that there is no greater case for the preservation of human dignity than the prevention of the disgrace and shame that would result from a deaf man's inability to hear those who wish to speak to him. It is difficult to describe the enormity of the humiliation, shame, and discomfort he would experience mingling with people and attending the synagogue, unable to hear or answer others, isolated by his condition. This is a greater infringement of human dignity than the cases mentioned above. Furthermore, his shame includes great mental anguish due to his inability to participate in public prayers and hear the reading of the Torah, as well as many other mitzvot. Therefore, it is clearly permissible to transport muktza in order to preserve human dignity of this high a degree. The deaf may therefore wear a hearing aid on Shabbat.
The Kalkelet HaShabbat, discussing opening an umbrella on Shabbat, writes:
It is permissible to construct (a temporary structure) on Shabbat (in order to preserve) human dignity - (
We may conclude that if it will prove feasible to operate an electric wheelchair without violating any Torah prohibitions, it will be possible for an invalid to use it on Shabbat, and not feel isolated or imprisoned. As was mentioned at the onset, we were encouraged in our endeavors by two of the leading Torah scholars of
D. The Suggested Solution
1. The Grama Switch
One accepted procedure for solving the problems listed above is to introduce an indirect operation (grama), as the Shulchan Aruch (OH, 3 34,22) rules that a prohibited category of action on Shabbat performed through grama is permissible. The Rama limits the applicability of this ruling to cases of pressing need, e.g., monetary loss, etc.
The use of grama for a wheelchair is practical only for the main switch, i.e., in place of the key which connects the battery before the commencement of motion. During motion, this solution is impractical, since grama necessarily involves a delayed reaction: hence, controlling the motion and speed of the wheelchair cannot practically be performed using this method.
2. Spring Return
Before detailing the principles of the mechanism we devised, I would like to consider one aspect of the original control system of the wheelchair, which in itself raises the question whether there is any construction or completion of a utensil involved.
The joystick control of an electric wheelchair has a spring powered return, whereby the stick always returns to the neutral position. Movement of the wheelchair is effectuated by exerting force against the spring. The wheelchair stops on its own when that pressure is removed and the stick returns by itself to neutral.
The argument can be made that the action of the invalid, namely moving the joystick, will not fall under the categories of construction or completing a utensil, since the resulting activity - the movement of the wheelchair - is not permanent and is sustained only as long as pressure continues to be exerted. If one would place a brick on top of another in such a way that it would remain in place only as long as one continued to hold it, it is extremely doubtful that this could be considered even a temporary construction. The same holds true for completing a utensil and makeh bepatish - nothing has been completed if the product is unable to exist on its own.
Rav Shlomo Zalman Auerbach raised this argument in reference to a flashlight, even though in that case the light does persist until the battery is exhausted (Kovetz Maamarim Belnyanei Chashmal, p.68).
Nonetheless, as this reasoning is unsupported by classical sources, we did not rely on it. Our solution assumes that, for all practical purposes, the joystick has the same status as a conventional electric switch, whose operation can be permitted only through grama.
3. Modulating the Current
In the original control mechanism found in most wheelchairs, the battery and the motor are mechanically disengaged by relays when the joystick is in neutral. Moving the stick closes the relay contacts which connect the battery current to the motor system. This is analogous to closing the switch commonly used to turn on household lighting, which was the original subject of the Chazon Ish's prohibition.
Our suggestion for Shabbat operation was a system where the commencement of operation would be accomplished, as mentioned above, through grama. Subsequently, all steering, braking, and acceleration would be
accomplished solely by modulating the level of the existing current. The entire system is built using semiconductors (transistors), where switching is accomplished by changing conductivity rather than mechanically.
The Chazon Ish, in his letter to Rav S.Z. Auerbach (Kovetz Maamarim BeInyanei Chashmal. p.61), suggests two reasons to include electricity under the category of construction:
Fulfilling the nature of the wire by the connection whereby the detached wire becomes one body together with the generator should be prohibited as construction: a) Because parts are being joined, and the looseness of the connection is irrelevant, since the electric current joins them and it is considered "firm"; b) Causing the wire to change from "death to life" is itself an act of construction.
In the system described above, which contains no mechanical switches, there is no physical joining of wires to the source of the electricity. All the parts are permanently connected from the beginning, and switching is accomplished by modulating the conductivity of the units, beginning with a low resistance, which permits high current, to very high resistance, which does not permit any current at all.
4. Minimal Current
Furthermore, we arranged that even when the stick is in "neutral", a minimal current is maintained throughout the system capable of moving the wheelchair at a "crawl." In this situation, one can no longer speak of changing the wire from a state of "death to life", as the system is always "alive", albeit at a very low level.
The same consideration applies to the prohibition of makeh bepatish advanced by the Tzitz Eliezer, who writes that turning on a hearing aid "falls under the prohibition of completing a utensil, as pressing the button and connecting the membrane to the electricity of the battery introduces a flow of life into all parts of the mechanism, which previously was considered a dead body...." Since in our suggestion there exists a low current all the time, either because it has been turned on before Shabbat or because it is started on Shabbat through a grama switch, it cannot be considered a dead body, and hence does not fall under the prohibition of completing a utensil.
It is necessary to use a mechanical brake in order to overcome the forward motion present at all times due to the minimal current. At times, the weight of the invalid sitting in the chair will be sufficient to prevent this crawl, whereas
the empty chair will crawl forward.
The following graphs depict the voltage on the motors in relation to the voltage of the battery.
5. Changing the Duty Cycle
A number of technological problems were apparent in the original model developed. Furthermore, it was not applicable to all commercially available wheelchairs. Consequently, a new model was developed which raised a new halachic point.
The first model ran on the direct current supplied by the battery to the motor through bipolar transistors. The new model utilized a circuit which converted the direct current supplied by the battery to alternating current, with a square wave at a frequency of 18,000 Hz. The voltage at the motor alternates 18,000 times a second, through a FET transistor bridge. When the stick is in neutral, the positive and negative periods of the motor's voltage cycle are equal. Since the motor is designed for direct current of a given polarity, turning in one direction for negative polarity and in the other for positive polarity, the net result is that the measurable voltage is the mean voltage, namely zero. Each second, the motor receives 18,000 voltage jolts of altercating polarity but equal force, and therefore does not turn at all.
In order to demonstrate that real voltage is present, even when the motor is in neutral, one may connect an electric bulb parallel to the motor. The bulb will light up, as it is designed to operate on alternating current.
Moving the joystick changes the ratio between the negative and positive phases of each cycle. This is called changing the duty cycle. Forward movement is accomplished by lengthening the positive section of the wave and shortening the negative (diagram 2): reverse motion is accomplished by the opposite ratio. Whenever the ratio of the positive to the negative differs from 1:1, the mean
voltage differs from zero, and the motor turns accordingly. The control over the change in ratio is continuous, thus enabling complete control over the speed and direction of the wheelchair through change in current without any switching. Furthermore, there is never a state of zero current, as described above, and the system always possesses a minimum current, as there is always a slight imbalance between the positive and negative phases.
This model provides a reliable and appropriate solution for every wheelchair available today. The halachic question that arose is the following: Does the change in the shape of the wave have the same status as a change in the level of current, as described above; i.e., does it avoid the problems of "construction" and "completion of a utensil"? Secondly, does the existence of alternating current capable of lighting an electric bulb constitute a completed construction, so that a change in the nature of the wave does not "change the wire from death to life", despite the fact that the motor, which is the system presently connected to the circuit, is completely dormant in this stage:
Rav Shlomo Zalrnan Auerbach, Rav Shaul Yisraeli, and Rav Yehoshua Neuwirth answered the first question in the affirmative, equating the change in the wave with a change in the voltage level of a direct current.
Concerning the second question, no decision was reached whether the concept of ”from death to life" relates to the circuit, in which case the system is in effect "alive": or to the final result, and the system is essentially "dead" if there is no revolution of the motor, so that starting motion would be prohibited.
This problem was overcome by introducing a minimum forward motion when the stick was in neutral. This solution would not be applicable for an invalid able to use only one hand who could not control the forward crawl with a mechanical brake. In that case, a resolution of the second question would be necessary.
 The original case of construction refers to building a house or a similar structure which is permanently attached to the ground. This is considered a stronger case of construction than making a movable object. In this case, the Chazon Ish claims that a completed electric circuit, since it is connected to the structure of the house itself, is more comparable to the archetype of construction than making a utensil. - tr.
 In the category of construction, the Halacha distinguishes between attaching a part in a loose or a firm manner. In this case, the Chazon Ish claims, the actual nature of the connection of the wires is not relevant. - tr.
 Various objects may not be moved on Shabbat, even if no category of forbidden creative activity is transgressed. This is called muktza. - tr.
 It is prohibited to ignore a lost object in the street and not pick it up in order to return it to its owner. The Talmud states that an old man for whom this would be beneath his dignity is not obligated. - tr.
 There is a common misconception that any delay automatically confers on an operation the status of grama. This is not correct. If the final reaction is a direct, though delayed, result of the original action, for instance, if a spring at the end of its unwinding were to perform an action, this would be considered the direct action of the initiator. Grama is the conjunction of a human action with a cause not originated by a man, such that only together is the intended result, after a delay, produced.