The day before yesterday I was told that my mother had slipped from her reclining lift chair at the nursing home where she lives and had lain for an hour on the floor before she was discovered. Mom who is very clear in her mind suffers from Parkinson's and has lost most of the movement in her body muscles. She spends all of her time either in a wheel chair which she can't move or in her Lift Chair Recliner with a hand held remote. She still has enough control of her hands so that with great effort she can use the remote to raise, lower and adjust the chair to suit her comfort. This seemingly minor control that she still has is very important to her. The cause of her falling from the chair was a combination of the design of the chair and her inability to let go after she has grabbed something with her hand. Here are three pictures of the chair which is designed primarily for elderly people who have trouble getting to their feet from a sitting position.
Chair is in the up right position.
The Chair in the fully reclined position. This is where she sleeps.
This is the full lift position that produced the fall. She was trying to adjust the recline position, slightly, at 2AM when she found that she could not release her grip on the "UP" button of the chair. With no ability to move her feet or legs, or to stand, the chair dumped her onto the floor much as a dump truck dumps its load of material on the ground. Fortunately, she only received minor bumps and bruises.
Her caretakers at the nursing home however were afraid that she would hurt herself the next time and so they took the remote control away from her. They were correct in taking it away but I could see that the loss of the remote was going to be a serious blow to her generally happy and healthy attitude.
The chair is powered by an external power supply that converts the 120VAC Main to 12 Volts DC. If you look closely in the above pictures you can see it hiding behind the wrung of the folding chair against the wall. The circuitry of the chair includes a Main Board with attachments to the single motor drive actuator, the heating pad, two massage motors, and the remote control. I knew if I was going to be able to put the remote control back in her hands I would have to find a way to allow her to control the movement of the chair from the Upright Sitting Position to the Full Recline Position but block any movement to the Full Lift Position. The problem was slightly complicated as the Full Lift Position was still needed by the nursing home staff for getting her out of the chair and onto a hydraulic lift that is used to change her from chair to wheel chair and for other needs.
An examination of the mechanics of the chair revealed that the frame of the seat stayed within 4 cm of the floor for the Upright and Recline positions but rapidly lifted for movement to the Lift Position.
The black L shaped metal bar that goes out to the wood frame stays within 4 cm of the floor during Upright and Recline Positions.
The same black bar is raised out of the picture in this photo of the Full Lift Position.
It was decided that the best solution would be to attach a limit sensor switch to the structural bar so that as long as the chair was in the Upright or Recline Positions the switch would be closed and signals from the Remote Control to the Main Board would pass normally. Once the chair began to go to the Full Lift Position however the limit switch would open and break the UP signal from the remote control stopping the upward travel. I returned to the shop with measurements and the remote control so that I could make a limit switch for the chair frame and determine which of the 9 wires from the remote was being used to make the chair go up.
This is the back side of the remote control circuit board. I was really surprised at the level of technology in the Lift Chair. The IC at the top of the picture is a PIC 16F505 microcontroller. A data sheet for the PIC was pulled from the internet. The power supply for the chair was 12 volts but it was not known if the voltage regulation to 5.5V or less to supply the PIC was being done on the main board or on the remote board. The Vcc and Vss of the PIC was determined and traced back to the proper wires. I found it convenient to feed power to the control by clipping onto a small bypass capacitor. The voltage was slowly raised while watching the voltage at the Vcc and Vss pins of the PIC. When the input voltage arrived at 5.5 volts the PIC was also at 5.5 volts and it was assumed that the regulation was being accomplished at the Main Board and the 5 volts was being supplied to the remote from there.
With the remote control powered up it was easy to push the UP and Down buttons and watch the changes on each of the wires leading from the remote. Experimentation revealed that the White wire carried the signal for the UP movement of the chair. In this case 0 volts or LOW was normal. 2 volts or High was the signal to the Main Board to run the motor actuator in the direction to raise the chair. The White wire in the remote cord would be my target for control of the Upward movement of the chair. By now the solution to how the staff of the nursing home would be able to use the Full Lift Position had also revealed itself. A momentary normally open push button would be wired across the limit switch in the base so that anyone who could reach the push button would be able to hold it down while simultaneously pushing the UP button of the remote control. The momentary push button would complete the circuit and the chair would continue up to the Full Lift Position.
Here is a schematic of the simple modifications that would be needed.
As soon as possible the next day I returned to the nursing home with the following items:
Limit Switch for the Base
Momentary pushbutton in a small box. Incidentally the push button was salvaged from a Gendex Panoramic X-Ray Machine and the Limit switch came from a Pin Ball machine that was salvaged out 50 years ago. The small black box housing the momentary switch came with a KaVo dental handpiece turbine.
Here is the limit switch installed on the frame of the chair.
This is the wire harness from the remote with the White Wire prepared for connection to the Limit and Momentary switches.
Finally here is the Lift Override Button attached to the back of the chair out of reach of anyone except the caregivers.
I would have wished to include a picture of Mom happily using the Chair without any further fear of being dumped on the floor but she is a little shy and would not consent. Suffice it to say that things are back to normal at the Nursing Home at least until tomorrow or the next day when her progressive illness will present its next challenge.
Thanks John
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