The Mystery in the Design of A. R. Guilmet

Transcription

1 The Mystery in the Design of A. R. Guilmet Everybody loves a good mystery. Today, fortunes are made de- Based on my measurements, the I ll bet Guilmet did the same thing. vising television shows, movies, suspension point would need to be and books with mysterious plots. moved back by only 1/1,000th of In the late 1880s the Society des an inch away from the direction of Horologers helped satisfy the desire for mystery through ingenious replace the loss. swing at the end of every swing to devices, including A. R. Guilmet s Let us look at it another way. mystery clock. Take a pendulum and suspend it Guilmet was a creative engineer who designed practical me- will hang stationary under the sus- from a point. The pendulum bob chanical devices and held several pension point. Now move the suspension one inch to the right. The patents, or brevets, for clocks and electric motors, but he wanted to bob will start to swing to the right design a clock that would mystify of center under the suspension. observers. If the works didn t seem However, a body in motion will connected to the pendulum, people would wonder how the clock dulum will continue to the right, tend to stay in motion ; the pen- kept time. Because everyone knew passing left under the suspension that a pendulum must have an impulse to keep it going, he needed to any losses, to the right of the sus- point to a point one inch, minus devise a very accurate clock with a pension point. Now at this point pendulum that oscillated continually with no apparent power or at- back to the left, where it started. move the suspension one inch tachment to the hands. Guilmet At this moment the bob would figured it out and left it to others to be approximately two inches to decipher the mystery. the right of the suspension point. How did he do it? He must have If you kept this up, the pendulum would swing to its maximum thought of the principle that a free pendulum, held a distance away swing. If you try this with a ball on from the vertical (say point A) a string, you will find that timing possesses a certain amount of potential energy and wants to swing to keeping the ball in motion. You your hand movement is essential back to the vertical. This energy An A. R. Guilmet mystery clock, ca. late 1880s. will also find that the amount of is proportional to the distance the hand movement is not very much pendulum is away from the vertical line under the point to keep the oscillation going. of suspension. A free-swinging pendulum will lose a bit To replace the loss in amplitude of each swing, it would of the swing distance with each swing due to external only be necessary to move the suspension point back and losses. If he could devise a way to make up for the loss forth by 1/1,000th of an inch. If the suspension point of each swing, the pendulum would continue to swing. is moved more than one 1/1,000th inch, the angle and Guilmet s solution was to move the suspension point the energy are increased and the swing of the pendulum away from the end of the swing by the amount of the increases. The increase in path also causes an increase in loss of each swing. losses. If the movement of the suspension is within the To satisfy my curiosity, I took a mystery clock I was limits of the pendulum swing, the swing distance equalizes to be constant at some point. repairing and mounted the statue with the pendulum so that the tip of the pendulum could be seen free swinging I have seen this difference in swing among the several in front of a ruler. It was not very scientific, but I only Guilmet statue clocks I have repaired. The movement of wanted a rough estimation of the decrease in the swing the suspension point can be adjusted from 1,000th to for 500 oscillations, or 1,000 swings, of the pendulum. I 2,000th of an inch. The amplitude of the pendulum is counted 500 complete oscillations, and the decrease was increased with greater movement of the arm, but the motion of the arm holding the suspension of the pendulum less than an inch. Therefore, the amount of swing loss with each swing was a little less than 1/1,000th of an is imperceptible to the eye. inch. The loss of each swing was imperceptible to the eye National Association of Watch and Clock Collectors, Inc. Reproduction prohibited without written permission. by Robert Boyd (NH) NAWCC Watch & Clock Bulletin September/October

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3 After working out the above reasoning, Guilmet had to design a mechanism that could sense the position and direction of swing of the pendulum. It was not an easy task. The suspension arm s movement must be the opposite of the direction of the pendulum swing and occur near the end of the swing. He achieved this action by a clever sensing mechanism that detects the pull on the statue arm by the pendulum. The swinging pendulum not only pulls down on the suspension point, but, when swinging, pulls horizontally. He mounted the statue on a base that could rotate on its vertical axis. The statue s arm, with the suspension point of the pendulum, is like a wrench on a pipe you are going to turn. Any sidewise pull on the arm will result in a twisting force on the statue. A like axis arm (see 1 in Figure 1A) inside the bottom of the base, points out from the swivel axis and protrudes inside the works. The end of this arm is fitted with a small ball (2) that penetrates the clockworks. This four-inch-long arm mimics the arm on the statue, transmitting any sidewise pull of the pendulum to the small ball at its end. The ball protrudes into a slot in the bottom of a long crutch (3) running up the front plate of the works, and the crutch is pivoted at the bottom of the works (4) a short distance from the point of contact of the ball. The lever ratio from the ball is about 1:24 to the slot at the top end of this crutch (5). This long lever gives a sensitivity advantage to any lateral movement of the ball. There is a pin attached at the top point of the stirrup (6) that extends through a slot in the trapeze (7) and extends into a slot in the top of the crutch (5). The slot in the trapeze has clearance on each side for the pin to pass through. This clearance is very important to the sensing because it allows the upper end of the crutch and stirrup pin to move slightly sideways without having to move the trapeze. The pin on the stirrup is less than half the distance from the stirrup pivot point to the bottom of the stirrup, allowing the bottom of the stirrup to move twice the distance the pin moves. This series of levers makes the lower part of the stirrup very sensitive to any lateral motion of the ball. The overall ratio from the statue s hand to the lower part of the stirrup is more than 1:100. This lever ratio allows the works to sense the sideways and directional pull of the pendulum as it passes through the center of its swing. In actuality, you can move the pendulum less than ±10 degrees off center, and the stirrup pallets will move to the right or left enough to clear the pin and release the crank. The lateral movement of the stirrup is limited by the clearance of the pin through the slot in the trapeze. The stirrup can t move the trapeze because the long leg of the trapeze is coupled to the crank on the end of the last pinion of the works, defining the limits. From Figure 1A, if the pendulum moves to the left of center, the lower part of the stirrup will also move to the left. From Figure 4A (see page 520), if the pendulum moves to the right, the lower stirrup will move right. Because of the 100:1 ratio of the levers, the statue s hand would have to move only.0002" to move the stirrup.020". The statue is a very sensitive lady! This sensitive series of levers was the key to Guilmet s mystery of the pendulum, which seemed to be completely detached from the works. Without any apparent connection, the works could detect when the pendulum was starting its swing from center in either direction and trigger the direction and movement of the suspension. This very clever lever and trapeze mechanism synchronized the pendulum with the clockworks and timed the movement of the suspension point. It should be noted that if the works are not well cared for or out of adjustment, the clock may run and the crank turn erratically but not be synchronized with the pendulum; this could cause it to either stop or run erratically. With synchronizing done, the movement must now impart the movement of the suspension point. The bottom tips of the stirrup have on either side a flat pallet that stop and hold a pin on a crank (8). Two crank pins (8 and 9), one at each end of the crank bar, are slightly offset from each other. Each pin is aligned with the position of one of the stirrup pallets (see Figure 1A). The pull of the pendulum swing to the left side of center is sensed through the levers and causes the slight movement of the stirrup to the left. Remember that the wide slot in the trapeze allows the stirrup to be moved without any Front of movement showing pendulum sensing mechanism. NAWCC Watch & Clock Bulletin September/October

4 10 9 movement of the trapeze. The pin on the crank will fall off the pallet and the crank will start to rotate clockwise one-half turn, powered by the works (Figure 2A). Now it is the movement s turn to move the statue. As the crank rotates clockwise, it moves the lower end of the long arm of the trapeze to the left. As the trapeze swings to the left, it will contact the pin on the stirrup (10 in Figure 2A) and move the top of the crutch to the left, causing the lower part of the crutch to move the ball slightly to the right. Here the movement of the stirrup-to-statue ratio is reversed, and the statue s hand movement is about 1/100 the movement of the top of the crutch. The hand rotates only about 2/1,000ths of an inch to the right, opposite to the direction of the swing. The movement is not perceptible to the eye. Those who want to analyze a complete cycle may look at Figures 3A and 4A to see the sensing of the pendulum moving back to the right as it repeats the process of sensing and movement of the statue arm back to the left. My Guilmet pendulum beats around 7,200 b/hr. Other Guilmet Clocks Guilmet s clocks won top prizes at the Societe des Horologers in He made many improvements to his clocks, mainly in the trapeze. The later trapeze arrangement is shown below in Figures 1B and 2B. It basically works the same way. Guilmet also made several versions of a torsion pendulum clock. The rotation of the 520 September/October 2013 NAWCC Watch & Clock Bulletin

5 pendulum is sensed by the same trapeze arrangement, but the works are very similar, although smaller in size, and he eliminated the last gear and pinion in the train and mounted the crank on the next to last. The rotation of the crank is counterclockwise and moves faster but less often, because the period of the torsion pendulum is much longer. I measured 1,860 b/hr on a large statue holding the clock above her head. The clock has a bracket at the bottom holding the top of the suspension spring, which gives the spring an imperceptible twist in the opposite direction of the pendulum rotation. Guilmet s clocks were not only mystifying but also very accurate. When set up properly, they maintain accuracy of better than a minute a week. Most methods of giving impulse to pendulums also impede their free swinging. Guilmet s method of moving the suspension to make up for free-swinging losses is ingenious because it does not interfere with the free motion of the pendulum, yet gives a very precise impulse that is not affected by the power of the works. Other than turbulence and external vibrations, Guilmet s method is very close to a free-swinging pendulum. These clocks are usually very heavy, which helps reduce the variability of vibration. A sturdy shelf also helps. This Clock In Action Readers interested in seeing the movement mechanism decribed in this article in action should access the addenda to this article at: watch-a-clock-bulletin/w-a-c-bulletin-addenda. About the Author Bob Boyd grew up in Indianapolis, spent about 40 years in New Jersey, and has enjoyed the last 20 in New Hampshire. A graduate of Purdue with an MBA from the University of Michigan, he s a retired professional engineer who specialized in electro-mechanical design. He s been a member of the NAWCC for about 45 years, and started collecting clocks a few years before becoming a member. Bob enjoys repairing complicated movements using CAD to design the lost parts and then make them using a gearcutter and other tools he has made. He figures out what the maker intended by using the spacing of old pivot holes, and sometimes shadows on the plates, along with a bit of math. He especially welcomes the challenge of designing and reconstructing missing or broken parts. He welcomes all to his extensive workshop and will provide plenty of talk and information about clocks. Indeed, sharing his love of clocks and how they work has led to many wonderful and far-flung friendships. He d love to hear your comments about this article, or any other clock topic at bobboyd@rlbpab.com. NAWCC Watch & Clock Bulletin September/October